DZS 907-1 : 2015

ISC

Edition1

Draft for Public Comment

Zambian Standard

ELECTRICITY DISTRIBUTION INFRASTRUCTURE - APPLICATION

GUIDE

Part 1: Construction (Design, Selection, Installation and Commissioning)

ZAMBIA BUREAU OF STANDARDS

This draft standard is for public enquiry only.

It must not be used or referred to as a Zambian

Standard

DZS 907-1:2015

i

DATE OF PUBLICATION

This Zambian Standard has been published under the authority of the Standards Council of the

Zambia Bureau of Standards on ……………….

ZAMBIA BUREAU OF STANDARDS

The Zambia Bureau of Standards is the Statutory National Standards Body for Zambia

established under an Act of Parliament, the Standards Act, Cap 416 of 1994 of the Laws of

Zambia for the preparation and promulgation of Zambian Standards.

REVISION OF ZAMBIAN STANDARDS

Zambian Standards are revised, when necessary, by the issue of either amendments or of revised

editions. It is important that users of Zambian Standards should ascertain that they are in

possession of the latest amendments or editions.

CONTRACT REQUIREMENTS

A Zambian standard does not purport to include all the necessary provisions of a contract. Users

of Zambian standards are responsible for their correct application.

TECHNICAL COMMITTEE RESPONSIBLE

This Zambian Standard was prepared by the Technical Committee TC 5/7 on Electricity

Distribution Infrastructure upon which the following organizations were represented:

Copperbelt Energy Corporation Plc (CEC)

Energy Regulation Board (ERB)

Engineering Institution of Zambia (EIZ)

Kansanshi Mining Company Plc (KMP)

Konkola Copper Mines Plc (KCM)

Lunsemfwa Hydro Power Company Plc (LHPC)

Department of Energy, Ministry of Mines, Energy and Water Development -

Rural Electrification Authority (REA)

University of Zambia (UNZA)

Zambia Bureau of Standards (ZABS)

ZESCO Limited

Zambia Bureau of Standards Email: zabs@zamnet.zm /infozabs@zamnet.zm

Lechwe House website: www.zabs.org.zm

Freedom Way South End

P.O. Box 50259, Lusaka

DZS 907-1:2015

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CONTENTS

FOREWORD ...............................................................................................................................................v

INTRODUCTION .......................................................................................................................................1

1. SCOPE ...............................................................................................................................................2

2. NORMATIVE REFERENCES .......................................................................................................2

3. DEFINITIONS AND ABBREVIATIONS ......................................................................................3

3.1 Definitions ................................................................................................................................3

3.2 Abbreviations and Acronyms ...................................................................................................5

4. NETWORK PLANNING AND DESIGN .......................................................................................6

4.1 General ......................................................................................................................................6

4.2 Substation Equipment and Component Sizing .........................................................................8

5. SUBSTATIONS .................................................................................................................................9

5.1 Transformers .............................................................................................................................9

5.2 Switchgear ..............................................................................................................................15

5.3 Busbars ...................................................................................................................................43

5.4 Controlgear .............................................................................................................................46

Equipment .......................................................................................................................................67

5.5 Auxiliary Equipment ..............................................................................................................67

6. CABLES AND CONDUCTORS ....................................................................................................68

6.1. General ....................................................................................................................................68

6.2. Fault currents and short-circuit ratings of cables ....................................................................68

7. OVERHEAD DISTRIBUTION LINES ........................................................................................72

7.1 General ....................................................................................................................................72

7.2 System Voltages .....................................................................................................................72

7.3 Conductors ..............................................................................................................................72

7.4 Support Structures ..................................................................................................................74

7.5 Insulators.................................................................................................................................77

7.6 Aerial Guard Earth Wire .........................................................................................................80

7.7 Anti-climbs .............................................................................................................................80

DZS 907-1:2015

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7.8 Cradle Catch nets ....................................................................................................................80

7.9 Red Balls .................................................................................................................................80

7.10 Goal posts ...............................................................................................................................81

7.11 Pole Mounted Equipment .......................................................................................................81

8. UNDERGROUND DISTRIBUTION SYSTEMS .........................................................................85

8.1. Components ............................................................................................................................85

8.2. All joints shall comply with IEEE 404, IEC 60840 and SANS 10198-9 to 11. Trenches: ...85

8.3. Cable Trays/Racks ..................................................................................................................86

8.4. Cable Route Markers ..............................................................................................................86

9. EARTHING AND LIGHTNING PROTECTION REQUIREMENTS .....................................87

9.1. General ....................................................................................................................................87

9.2. Earthing of Equipment ............................................................................................................87

9.3. Lightning protection ...............................................................................................................94

9.4. Insulation Co-ordination .........................................................................................................94

10. VOLTAGE REGULATORS ..........................................................................................................95

10.1. General ....................................................................................................................................95

10.2. Secondary Transformer Voltage Regulation ..........................................................................95

11. CAPACITORS ................................................................................................................................96

11.1. Power Capacitors ....................................................................................................................96

11.2. Shunt Capacitors .....................................................................................................................96

11.3. Capacitor Banks ......................................................................................................................96

12. FEEDER PILLAR ........................................................................................................................102

12.1. General ..................................................................................................................................102

12.2. Specification for Feeder Pillars .............................................................................................102

13. SUBSTATION CONCRETE WORKS .......................................................................................104

13.1 General ..................................................................................................................................104

13.2 Substation equipment plinths ................................................................................................104

13.3 Oil containment tanks ...........................................................................................................105

14. WAYLEAVE .................................................................................................................................106

14.1. General Requirements...........................................................................................................106

DZS 907-1:2015

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14.2. Specific requirements ...........................................................................................................106

14.3. Prevention against Animal diseases ......................................................................................108

15. LONG-TERM PRESERVATION OF SUPPORT STRUCTURES FOR DISTRIBUTION

INFRASTRUCTURE ...................................................................................................................109

15.1 Painting .................................................................................................................................109

15.2 Concrete Poles ......................................................................................................................109

15.3 Steel Poles .............................................................................................................................109

15.4 Steel Structures for Outdoor Substations ..............................................................................109

APPENDICES .........................................................................................................................................110

APPENDIX 1: INFORMATION REQUIRED WITH TRANSFORMER ENQUIRY AND

ORDER 110

DZS 907-1:2015

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FOREWORD

The Zambia Bureau of Standards (ZABS) is the Statutory Organization established by an Act of

Parliament. ZABS is responsible for the preparation of national standards through its various technical

committees composed of representation from government departments, the industry, academia,

regulators, consumer associations and non- governmental organizations.

This National standard has been prepared in accordance with the procedures of the ZABS. All users

should ensure that they have the latest edition of this publication as standards are revised from time to

time.

No liability shall attach to ZABS or its Director, employees, servants or agents including individual

experts and members of its technical committees for any personal injury, property damage or other

damages of any nature whatsoever, whether direct or indirect, or for costs (Including legal fees) and

expenses arising out of the publication, use of, or reliance upon this ZABS publication or any other ZABS

publication.

Compliance with a Zambian standard does not of itself confer immunity from legal obligations.

DZS 907: 2015 was prepared by the TC 5/7 on Electricity Supply

1

ZAMBIAN STANDARD

ELECTRICITY DISTRIBUTION INFRASTRUCTURE – Application Guide

Part 1: Construction (Design, Selection, Installation and Commissioning)

INTRODUCTION

This standard provides a set of guidelines for the design, construction and installation and

commissioning of electricity distribution infrastructure within Zambia. These guidelines are to

be applied to all publicly and privately owned electricity distribution infrastructure, so as to

ensure safety and quality electricity distribution within Zambia.

Electricity distribution infrastructure needs to be planned, designed, constructed, maintained and

operated in accordance with the requirements, standards and guidelines provided in the

approved standards document to achieve the set objectives of equipment reliability, safety,

providing quality service to the consumer and meeting the environmental protection

requirements.

The quality and reliability of the installed infrastructure is of paramount importance and

compliance to set standards will help achieve the objective of reliability and security of supply,

safe operation and safety of the consumer and the general public.

Therefore, the focus of this standard will be on quality of electrical components and other

accessories and requirements for installations of these components in the distribution system.

The standards are intended to ensure that: components are able to be interchanged without any

deviation; there is minimum interruption on the service delivery to the consumer and that the

utilities‟ expenditure on electrical components replacements is reduced due to increased life of

the components.

This standard is expected to achieve the following:

i). Electrical equipment design and construction in accordance with good engineering

practices;

ii). High operational reliability owing to good quality material and installation;

iii). Reduction on maintenance costs;

iv). Improvement of the quality of service delivery to consumer;

v). Promote product upgrade and technological innovation in the electricity supply industry

in Zambia;

vi). Control on the quality of electrical products on the market;

vii). Operational safety;

viii). Electrical equipment designed for use within certain voltage limits that is safe to use;

and,

ix). Environmental protection.

2

1. SCOPE

This part of DZS 907 covers the planning, design, construction, installation, and commissioning

of ac distribution networks ranging from three phase 33,000 volts to 220 volts a.c. single phase.

It is a general guide to good technical practice for economical overhead and underground

distribution networks in Zambia.

This standard excludes power supply to mining underground power distribution and other zoned

and categorized areas e.g. explosive environments, solvent extraction plants, military

installations and flammable environments.

2. NORMATIVE REFERENCES

The following standards contain provisions which, through reference in this text, constitute

provisions of this part of DZS 907. All standards are subject to revision and since any reference

to a standard is deemed to be a reference to the latest edition of that standard party to

agreements based on this part of DZS 907 are encouraged to take steps to ensure the use of the

most recent editions of the standards indicated below.

Information on currently valid national and international standards can be obtained from Zambia

Bureau of Standards.

IEV 441-18-09

IEV 441-18-081

IEV 441-18-111

IEV 441-18-131

IEC 60

IEC60812

IEC 60865

IEC 60909

IEC 60050-195, 195-06-05

IEC 61024

IEC 62262 – IK Code

IEC 62305

IP Code - IEC 60529

IEC 61643

IEC 60071,

IEC60085,

IEC 60283,

IEC 60296,

IEC 60815,

IEC 61211,

IEC61467

IEC 60801- EMI & RFI,

EMC-IEC 61000

IEC 60947,

IEC 61363

IEC 61892

IEC 61439

3

IEC 62271

IEC 62357,

IEC 61850

ZS387

IEEE C57.12.00 - Standard General Requirements for Liquid-Immersed Distribution, Power,

and Regulating Transformers

ZS791- Wiring of Premises

ZS 746-1

ZS 746-2

3. DEFINITIONS AND ABBREVIATIONS

3.1 Definitions

3.1.1 Bund wall: A wall/barrier of sufficient height constructed around fluid filled

equipment to contain spillage of liquids.)

3.1.2 Busbar: a low-impedance conductor to which several electric circuits can be separately

connected.

3.1.3 Controlgear: general term covering switching devices and their combination with

measuring, protective and regulating equipment, also assemblies of associated control,

such devices and equipment with associated interconnections, accessories, enclosures

and supporting structures, intended in principle for the control of electric energy

consuming equipment

3.1.4 Cross-arm: a pole that is used in a horizontal or near- horizontal position in a structure

for the support of power distribution lines, but that is not intended to be used in contact

with the ground

3.1.5 Cut-out base: The fixed part of a cut-out provided with the contacts and terminals.

3.1.6 Degree of protection: The extent of protection provided by an enclosure against

access to hazardous parts, against. ingress of solid foreign objects and/or against

ingress of water and verified by standardized test methods

3.1.7 Direct contact: Contact of persons or livestock with live parts.

NOTE: This IEV definition is given for information. In this standard "direct contact" is replaced

by "access to hazardous parts ".

3.1.8 Drop-out fuse-link assembly [cut-out]: An assembly that comprises all components

that form a complete device intended to protect equipment or parts of a reticulation

system (or both), in which the fuse-carrier automatically drops into a position that

provides an isolating distance after the fuse has operated.

NOTE: In this specification the term “cut-out” is often used in place of “drop-out fuse-link”

assembly.

3.1.9 Enclosure: A part providing protection of equipment against certain external

influences and, in any direction, protection against direct contact.

4

NOTE: This definition taken from the existing International Electro-technical Vocabulary (IEV)

needs the following explanations under the scope of this standard:

1) Enclosures provide protection of persons or livestock against access to hazardous parts.

2) Barriers, shapes of openings or any other means - whether attached to the enclosure or formed

by the enclosed equipment - suitable to prevent or limit the penetration of the specified test probes

are considered as a part of the enclosure, except when they can be removed without the use of a

key or tool.

3.1.10 Expulsion fuse: A fuse in which operation is accomplished by the expulsion of gases

produced by the arc. [IEV 441-18-111]

3.1.11 Fuse element: That part of the fuse-link which is designed to melt under the action of

a current that exceeds some definite value for a definite period of time. [IEV 441-18-

081]

3.1.12 Fuse-carrier: The movable part of a fuse-link assembly designed to carry a fuse-link.

[IEV 441-18-131]

3.1.13 Fuse-link: The part of a fuse including the fuse element(s) intended to be replaced

after the fuse has operated. [IEV 441-18-09]

3.1.14 Hazardous live part: A live part which, under certain conditions of external

influences, can give an electric shock (see IEC 60050-195, 195-06-05).

3.1.15 Hazardous mechanical part :A moving part, other than a smooth rotating shaft, that is

hazardous to touch

3.1.16 Hazardous part: A part that is hazardous to approach or touch

3.1.17 Insulator: That component of a cut-out base, which is intended to insulate the load-

side and the source-side from each other and from earth and which is fitted with an

insulator-fixing stem.

3.1.18 Insulator-fixing stem: A component for attaching the insulator to the mounting L-

bracket.

3.1.19 IP Code: A coding system to indicate the degrees of protection provided by an

enclosure against access to hazardous parts, ingress of solid foreign objects, ingress of

water and to give additional information in connection with such protection

3.1.20 Lower contact: The load-side contact of a cut-out base, which also allows a

removable fuse-carrier or solid-link to pivot.

3.1.21 Mounting L-bracket: A device used to facilitate the mounting of a cut-out on either

a wooden cross-arm or a steel cross-arm.

3.1.22 Outdoor distribution cut-out: A drop-out vented expulsion fuse-link assembly or

solid-link assembly, together with the associated components.

3.1.23 Rated fibre stress: stress in the wood from the applied load just before breaking

5

3.1.24 Solid-link assembly: An assembly that comprises all components that form a

complete device intended to isolate equipment or parts of a reticulation system, or both,

from the source of supply.

3.1.25 Solid-link: A component for use in place of a fuse-carrier, to effect a manual

disconnection.

3.1.26 Spacer block: a piece of timber that is used as a spacer between poles and cross-arms

in five- pole structures but that is not intended to be used in contact with the ground

3.1.27 Substation- An enclosed assemblage of equipment, e.g., switches, circuit breakers,

buses, and transformers, under the control of qualified persons, through which electric

energy is passed for the purpose of switching or modifying its characteristics to

increase or decrease voltage or control frequency or other characteristics.

3.1.28 Switchgear: the combination of electrical disconnects switches, fuses or circuit

breakers used to control, protect and isolate electrical equipment. It is used both to de-

energize equipment to allow work to be done and to clear faults downstream.

3.1.29 Treated/treatment: impregnated/impregnation with an acceptable preservative

3.1.30 Upper contact: The source-side spring-loaded contact of a cut-out base.

3.2 Abbreviations and Acronyms

3.2.1 ACSR: Aluminium Conductor Steel Reinforced

3.2.2 ONAN: Oil Natural Air Natural

3.2.3 ONAF: Oil Natural Air Forced

3.2.4 OFAF: Oil Forced Air Forced

3.2.5 OFWF: Oil Forced Water Forced

6

4. NETWORK PLANNING AND DESIGN

4.1 General

The primary purpose of an electricity distribution network system is to meet the customer‟s

demands for energy. Depending on the geographical location, the distribution network can be in

the form of overhead lines or underground cables.

The objective of planning for the distribution network is to ensure that the required power

demand by the customers is met. However, to achieve this objective the designer of the network

should take into account the technical performance of the network being designed and its

associated costs so that the electricity distribution network is technically sound and cost

effective.

The factors influencing network design that need to be considered fall into the following three

categories;

a). Fixed parameters within which the electrical designer might have to work, include:

i). Statutory requirements:

Environmental Impact Assessment with ZEMA, Environmental Protection and

Pollution Act

Land Acquisition Act

Local Government Act

Town and Country Planning Act

Occupational Health and Safety Act 36 of 2010

Factories Act Cap 441

Electricity Act

Energy Regulation Act

Petroleum Act

Mines and Minerals Act

Water Resource Management Authority Act

Zambezi River Authority Act

Forestry Act

Civil Aviation Act

Zambia Wildlife Act

ii). Existing services:

Electricity Utilities

Water Utilities and sewerage

Information and Communication Technology service providers

Road Development agency

Local Authorities

Oil pipeline

Rail line

iii). Existing area layout:

7

Local Authority

Geological Survey

Planning and Buildings Department

ZAWA

iv). Nature of the terrain:

Topographic

Soil conductivity for earthing

Soil bearing capacity for civil works

v). Geographic location:

Proximity to sensitive infrastructures i.e. fuel storage tanks, storage magazines

or other explosive materials

Seismic Zones

Lightening prone areas

Existing infrastructures i.e. tall buildings, airport area

vi). Factors over which the designer has limited or no control, including:

Consumer loads;

Diversity;

vii). Factors over which the designer should exercise control, including:

Initial capital costs and life cycle costs;

New area layout;

Number and positioning of metering points;

Cable and conductor sizes and types of cable and conductor; and,

Number, sizes, locations and types of substation;

b). The designer shall obtain supply characteristics at the supply points from the service

provider i.e. Voltage drop and unbalance, within limits of design load, and all other

parameters as prescribed in the Zambian Power Quality Standard ZS 387

NOTE: No design should be considered in isolation. The planner should take into account the

relationship between the area to be supplied and adjacent supply areas, proposed future

developments and environmental considerations. When applying the guidelines to individual

schemes, it is necessary to take into account all local conditions and total life cycle cost (for

example, capital outlay and the upgrading of operational and maintenance requirements).

c). Climatic Conditions

Some examples of the effects of climatic conditions on overhead lines are:

i). Ambient temperature and wind affect the sag of overhead conductors and their

current-carrying capacity;

ii). Wind affects pole supports, stays and clearances;

iii). Lightning causes surge voltages to be induced into the network; and

iv). In cases where overhead lines are situated close to the coast, the combined effects

8

of pollution and high relative humidity on insulators have an adverse effect on

the system. Salt fog can be corrosive on conductors with steel reinforcing if not

adequately greased.

4.2 Substation Equipment and Component Sizing

A substation is a part of an electrical generation, transmission and distribution system. Its

primary purpose is to transform voltages from high to low, or the reverse, or perform any of

several other important functions. All substation equipment and associated components shall be

designed, constructed, installed and commissioned to meet the requirements as set out in this

standard.

The expected thermal, chemical, mechanical and environmental conditions shall be considered

in the design of the equipment. Further, all equipment shall be designed to withstand the effects

of normal, emergency and fault conditions expected during operation. The substation equipment

specified in this standard include; transformers, switchgear (circuit breakers, busbars,

fuses), control gear and substation auxiliary equipment (substation lighting, fire

suppression systems and telemetry).

The following safety considerations shall be taken into account in the planning, designing,

construction, installation and commissioning of substations in accordance with the provisions of

ZS 418 Parts 1 and 2:

i). Safety clearance

ii). Signage

iii). Fencing

iv). Personal Protective Equipment ( PPE)

v). Substation Perimeter

For other safety considerations refer to IEC 61558 on Safety of installations and IEC 61557

9

5. SUBSTATIONS

5.1 Transformers

5.1.1 General

All distribution transformers shall comply with IEC 60076- Power Transformers – All Parts.

In this standard, a transformer is an electrical device that transfers energy between two or more

circuits through electromagnetic induction.

The standard applies to three-phase and single- phase power transformers (including auto-

transformers) with the exception of certain categories of small and special transformers such as;

a). single-phase transformers with rated power less than 1 kVA and three-phase

transformers less than 5 kVA;

b). instrument transformers;

c). transformers for static convertors;

d). traction transformers mounted on rolling stock;

e). starting transformers;

f). testing transformers; and

g). welding transformers.

It‟s recommended that an agreement shall be reached concerning alternative or additional

technical solutions or procedures. Such agreement is to be made between the manufacturer and

the purchaser, the matters should preferably be raised at an early stage and the agreements

included in the contract specification.

5.1.2 General Design and Construction

This part of the standard prescribes the specific technical requirements applicable to

transformers.

NOTE 1: For the exact limit and acceptable tolerance of a particular parameter, this specification is to be

used in conjunction with the descriptions and the specifications of IEC 60076 Part 1, 2 and 3.

5.1.2.1 Service Conditions

The service conditions for transformer shall be as specified in Table 5-1 below:

Table 5-1: Service Conditions for Transformers

S/N Service Condition Specification

1. Altitude above mean sea level 1400m

2. Maximum ambient temperature for design purpose 40oC

3. Average ambient temperature for design purposes 30oC

4. Minimum ambient temperature for design purposes -1oC

5. Relative humidity maximum at 35oC 95%

6. Maximum wind speed 40m/s

7. Mean annual rain fall 1065mm

8. Maximum solar radiation 1200 W/m2

9. Isokeraunic Level average 130 days/year

10

5.1.2.2 Installation

Power transformers shall be so installed that all energized parts are enclosed or guarded so as to

limit the likelihood of inadvertent contact, or the energized parts shall be physically isolated.

The case shall be effectively grounded or guarded.

Oil-immersed transformers are to be hermetically sealed with integral filling. Oil in

transformers is used as insulation and also serves as a cooling medium.

The installation of liquid-filled transformers shall utilise one or more of methods highlighted

below to minimise fire hazards. The method to be applied shall be according to the degree of the

fire hazard. Recognised methods are the use of less flammable liquids, space separation, fire

resistant barriers, automatic extinguishing systems, absorption beds, and enclosures. The

amount and characteristics of liquid contained should be considered in the selection of space

separation, fire-resistant barriers, automatic extinguishing systems, absorption beds, and

enclosures that confine the liquid of a ruptured transformer tank, all of which are recognized as

safeguards.

i). Transformers and regulators 75 kVA and above containing an appreciable amount of

flammable liquid and located indoors shall be installed in ventilated rooms or vaults

separated from the balance of the building by fire walls. Doorways to the interior of the

building shall be equipped with fire doors and shall have means of containing the liquid.

ii). Transformers or regulators of the dry type or containing a nonflammable liquid or gas

may be installed in a building without a fireproof enclosure. When installed in a building

used for other than station purposes, the case or the enclosure shall be so designed that

all energised parts are enclosed in the case that is effectively grounded. As an alternate,

the entire unit may be enclosed so as to limit the likelihood of inadvertent contact by

persons with any part of the case or wiring. When installed, the pressure-relief vent of a

unit containing a non-biodegradable liquid shall be furnished with a means for absorbing

toxic gases.

iii). Transformers containing less flammable liquid may be installed in a supply station

building in such a way as to minimize fire hazards. The amount of liquid contained, the

type of electrical protection, and tank venting shall be considered in the selection of

space separation from combustible materials or structures, liquid confinement, fire-

resistant barriers or enclosures, or extinguishing systems.

5.1.2.3 External Clearances

External clearances shall be such that there will be no visible corona up to 1.1 pu system

voltage. In addition, the minimum external clearances between live parts and live parts to

ground shall not be less than that specified in ZS 418.

5.1.2.4 Identification

The transformer must contain a nameplate reverted on the tank and clearly visible. The

nameplate shall indicate:

11

The year of Manufacture

The standard to which the unit is made

Name of manufacturer

Serial number

Cooling type

Vector Symbol

Vector group diagram

Winding configuration diagram

Tap changer type (Onload/Offload)

Number of Taps and nominal Tap

Specific tap voltages

Inscribed Tested Voltage percent impedance

KVA rating

Frequency

Primary and Secondary Voltage at Nominal

Maximum Secondary and primary currents at Nominal

Weight of the oil

Weight of core and tank

Gross weight

5.1.2.5 Manufacturers’ Drawings

The following drawings approved by the purchaser shall be availed by the manufacturer:

Wiring and schematic drawing of the tap changer and transformer

Complete assembly drawing of the transformer and accessories

Foundation Drawings

Outline drawing

Instruction Manuals

An instruction manual shall be availed by the manufacturer composed of the

following sections:

Introduction

General Transformer features

Parking, Transportation and Handling

Assembling and Installation

Pre-commissioning checks

Commissioning

Maintenance

Troubleshooting

End of life disposal

Drawings and catalogue

Loss evaluation and Payment

12

Both No Load and Full Load losses shall be specified to the potential supplier of the

Transformer. The calculated and actual losses shall be compared during factory

acceptance test and payment may be calculated.

In the event of actual loss being higher than agreed, parties may agree on a price

discount or rejection of the unit.

5.1.3 Rating Characteristics

5.1.3.1 Transformer Rating

The transformer shall have an assigned rated power for each winding which shall be marked on

the rating plate. The rated power refers to continuous loading. This is a reference value for

guarantees and tests concerning load losses and temperature rises.

If different values of apparent power are assigned under different circumstances, for example,

with different methods of cooling, the highest of these values is the rated power.

A two-winding transformer has only one value of rated power, identical for both windings.

When the transformer has rated voltage applied to a primary winding, and rated current flows

through the terminals of a secondary winding, the transformer receives the relevant rated power

for that pair of windings.

The transformer shall be capable of carrying, in continuous service, the rated power [for a multi-

winding transformer: the specified combination(s) of winding rated powers] under conditions

listed in Clause 5.1.2.1 and without exceeding the temperature-rise limitations specified in IEC

60076-2.

5.1.3.2 Transformer Loading

The maximum loading of the transformer shall be specified at all cooling levels i.e. ONAN,

ONAF, OFAF and OFWF. The transformer will be loaded to not more than 1.5 times maximum

nameplate rating. All transformer parts shall be sized to allow full use of the winding's loading

capability for the following loading types (These loading capabilities shall apply to all

transformers for the following conditions):

i). Preload of 90 % of nameplate MVA rating;,

ii). The hottest spot temperature not to exceed 140º C, a top oil temperature not to exceed

110ºC; and,

iii). Loss of life not to exceed 1.0% per incident. Short Time Minimum Acceptable Loading

Capability p.u. of nameplate MVA rating.

The loadings are depicted in the Table 5-2 below:

Table 5-2: Transformer Loading

Ambient Temperature (oC) Load In Per Unit of Nameplate Rating

13

(Load Duration in Hours)

0.5 1.0 2.0 4.0 8.0

10 1.50 1.45 1.39 1.34 1.31

40 1.26 1.23 119 1.15 1.13

5.1.3.3 Short Circuit Capability

The transformer and its current-carrying parts including tap changers and bushings shall have

short circuit capability in accordance with IEC 60076-5. Tertiary Windings, when specified,

shall be self-protecting. System fault power may be supplied from either one or both unfaulted

terminals. The maximum short circuit current at the tertiary bushings shall not exceed either, 25

times the rated tertiary winding capacity or 32 kA whichever is lower.

5.1.3.4 Earthquake Strength

The completely assembled transformer shall meet the High Seismic Qualification Level with

2% which is the highest seismic reading in Zambia.

5.1.3.5 Wind Loading Strength

The transformer shall be designed to withstand winds up 40m/sec in its service configuration

(i.e., with bushings, arresters, radiator/coolers, conservator, etc. installed). The earthquake and

wind forces need not be considered as occurring simultaneously. Documentation in the form of

test data or calculations shall be provided to confirm the transformer‟s wind and mechanical

shock withstand capabilities.

5.1.3.6 Sound Level

The sound level shall not exceed 75db at full load

5.1.3.7 Vibration

The transformer accessories shall be protected from damage by vibration during operation,

transportation or short circuits

5.1.4 Transformer Auxiliary Equipment

The size, type and location of the transformer dictate the amount of auxiliary equipment

associated with it. All auxiliary equipment should be checked for proper operation to assure

they are not defective.

The following accessories shall be included on all oil filled substation transformers:

i). Pad lockable tap changer for de-energized operation ( for transformers greater than 1000

kVA rating)

ii). Upper filling plug and filter press connection

iii). Drain valve with a sampler (two-inch drain valve for transformers above 2500 kVA

rating)

iv). Dial type thermometer

v). Pressure/vacuum gauge [with] [without] bleeder connection

vi). Magnetic liquid level gauge

vii). Pressure Relief Valve/Device,

14

viii). Alarm contacts on [all gauges] [dial thermometer] [liquid level gauge] [pressure vacuum

gauge]

ix). Pressure relief diaphragm

x). Buchholz relay( for transformers greater than and including 1200 kVA rating)

15

5.2 Switchgear

Switchgear shall comply with IEC 62271-SER ed1.0 (2015-02) High-voltage switchgear and

control gear - ALL PARTS.

5.2.1. Normal Service Conditions

5.2.1.1 Indoor switchgear and controlgear

a). The ambient air temperature does not exceed 40 °C and its average value, measured over a

period of 24 h, does not exceed 35 °C.

The preferred values of minimum ambient air temperature are –5 °C, –15 °C and –25 °C.

b). The influence of solar radiation may be neglected.

c). The altitude does not exceed 1 000 m.

d). The ambient air is not significantly polluted by dust, smoke, corrosive and/or flammable

gases, vapours or salt. The manufacturer will assume that, in the absence of specific

requirements from the user, there are none.

e). The conditions of humidity are as follows:

the average value of the relative humidity, measured over a period of 24 h, does not

exceed 95 %;

the average value of the water vapour pressure, over a period of 24 h, does not

exceed 2.2 kPa;

the average value of the relative humidity, over a period of one month, does not

exceed 90 %;

the average value of the water vapour pressure, over a period of one month, does not

exceed 1.8 kPa.

For these conditions, condensation may occasionally occur.

NOTE 1: Condensation can be expected where sudden temperature changes occur in periods of

high humidity.

NOTE 2: To withstand the effects of high humidity and condensation, such as breakdown of

insulation or corrosion of metallic parts, switchgear designed for such conditions should

be used.

NOTE 3: Condensation may be prevented by special design of the building or housing, by suitable

ventilation and heating of the station or by the use of dehumidifying equipment.

f). Vibrations due to causes external to the switchgear and controlgear or earth tremors are

insignificant relative to the normal operating duties of the equipment. The manufacturer

will assume that, in absence of specific requirements from the user, there are none.

NOTE 4: The interpretation of the term “insignificant” is the responsibility of the user or specifier

of the equipment. Either the user is not concerned with seismic events, or his analysis

shows that the risk is “insignificant”.

Outdoor switchgear and controlgear

a). The ambient air temperature does not exceed 40 °C and its average value, measured over a

period of 24 h, does not exceed 35 °C.

The preferred values of minimum ambient air temperature are -10 °C, -25 °C, -30 °C and -

40 °C.

16

Rapid temperature changes should be taken into account.

b). Solar radiation up to a level of 1 000 W/m2 (on a clear day at noon) should be considered.

NOTE 1: Under certain levels of solar radiation, appropriate measures, for example roofing, forced

ventilation, test simulating solar gain, etc., may be necessary, or derating may be used, in

order not to exceed the specified temperature rises and design pressure limits.

NOTE 2: Details of global solar radiation are given in IEC 60721-2-4.

c). The altitude does not exceed 1 000 m.

d). The ambient air may be polluted by dust, smoke, corrosive gas, vapours or salt.

e). The ice coating shall be considered in the range from 1 mm up to, but not exceeding, 20

mm.

f). The wind speed does not exceed 34 m/s (corresponding to 700 Pa on cylindrical surfaces).

NOTE 3: Characteristics of wind are described in IEC 60721-2-2.

g). Consideration should be given to condensation or precipitations that may occur.

NOTE 4: Characteristics of precipitation are defined in IEC 60721-2-2.

h). Vibrations due to causes external to the switchgear and controlgear or earth tremors are

insignificant relative to the normal operating duties of the equipment. The manufacturer

will assume that, in the absence of specific requirements from the user, there are none.

NOTE 5: The interpretation of the term “insignificant” is the responsibility of the user or specifier

of the equipment. Either the user is not concerned with seismic events, or his analysis

shows that the risk is “insignificant”.

5.2.2. General Design and Construction

Switchgear can be of indoor and outdoor types.

Metal-enclosed switchgear and control gear shall be designed so that normal service, inspection

and maintenance operations, determination of the energized or de-energized state of the main

circuit, including the usual checking of phase sequence, earthing of connected cables, locating

of cable faults, voltage connected cables or other apparatus and the elimination of dangerous

electrostatic charges, can be carried out safely. An earthing conductor shall be provided

extending the whole length of the metal-enclosed switchgear and control gear. The current

density in the earthing conductor, if of copper, shall under the specified earth fault conditions

not exceed 200 A/mm2 for a rated duration of short circuit of 1 s and 125 A/mm

2 for a rated

duration of short-circuit of 3 s. However, its cross section shall be not less than 30mm2. It shall

be terminated by an adequate terminal intended for connection to the earth system of the

installation.

The metallic parts of a withdrawable part which are normally earthed shall also remain earth-

connected in the test and disconnected positions under the prescribed conditions for the isolating

distance and also in any intermediate position. The metallic parts of a removable part which are

normally earthed shall remain earth-connected until the removable part is separated from the

switchgear.

17

5.2.1.1. Shutters

Means shall be provided to ensure the reliable operation of the shutters, e.g. by a mechanical

drive, where the movement of the shutters is positively driven by the Movement of the

removable part. If, for maintenance or test purposes, there is a requirement that one set of

fixed contacts shall be accessible through opened shutters, all the shutters shall be provided

with means of locking them independently in the closed position or it shall be possible to

insert a screen to prevent the live set of fixed contacts being exposed.

When, for maintenance or test purposes, the automatic closing of shutters is made inoperative in

order to retain them in the open position, it shall not be possible to return the switching device

to the service position until the automatic operation of the shutters is restored.

This restoration may be achieved by the action of returning the switching device to the service

position. The shutters of the three types of metal-enclosed switchgear and control gear may be

either metallic or non-metallic. If shutters are of insulating material, they shall not become

part of the enclosure, If they are metallic, they shall be earthed, and if they become part of the

enclosure, they shall provide the degree of protection specified for the enclosure.

5.2.1.2. Interlocks

It shall not be possible to close the circuit-breaker, switch or contactor in the service position

unless any auxiliary circuits associated with the automatic opening of these Devices are

connected. Conversely, it shall not be possible to disconnect the auxiliary Circuits with the

circuit-breaker closed in the service position. Interlocks shall be provided to prevent operation

of disconnections under conditions other than those they are intended for.

The operation of a disconnector shall not be possible unless the associated circuit-breaker,

switch or contactor is in the open position. If earthing of a circuit is provided by a circuit-

breaker in series with an earthing switch, the earthing switch shall be interlocked with the

circuit-breaker and the circuit-breaker shall be secured against unintentional opening.

5.2.1.3. Earthing of Switchgear and Controlgear

5.2.1.3.1. Earthing of the main circuit

To ensure safety during maintenance work, all parts of the main circuit to which access is

required or provided shall be capable of being earthed prior to becoming accessible. This does

not apply to withdrawable and removable parts which become accessible after being separated

from the switchgear.

5.2.1.3.2. Earthing of the enclosure

Switchgear and controlgear shall be provided with a reliable earthing terminal having a

clamping screw or bolt for connection of an earthing conductor suitable for specified fault

conditions. The connecting point shall be marked with the "protective earth" symbol, as

indicated by symbol 5019 of IEC 60417. Parts of metallic enclosures connected to the

earthing system may be considered as an earthing conductor.

18

All metallic components and enclosures that may be touched during normal operating

conditions and are intended to be earthed shall be connected to an earthing terminal.

An earthing conductor shall be provided extending the whole length of the metal-enclosed

switchgear and control gear. The current density in the earthing conductor, if of copper,

shall not exceed 200 A/mm2 under the specified earth fault conditions; however, its cross-

section area shall be not less than 30 mm2. It shall be terminated by an adequate terminal

intended for connection to the earth system of the installation.

NOTE - If the earthing conductor is not made of copper, equivalent thermal and mechanical requirements should be met. In general,

the continuity of the earth system shall be ensured taking into account the thermal and mechanical stresses caused by the current it may

have to carry. The maximum value of earth fault currents depends upon the type of system neutral earthing employed and shall be

indicated by the user. Where earthing connections have to carry the full three-phase short-circuit current (as in the case of the short-

circuiting connections used for earthing devices) these connections shall be dimensioned accordingly.

5.2.1.4. Requirements for liquids in switchgear and control gear

The manufacturer shall specify the type and the required quantity and quality of the liquid to be

used in switchgear and controlgear and provide the user with necessary instructions for

renewing the liquid and maintaining its required quantity and except for sealed pressure

systems.

NOTE: Attention is drawn to the need to comply with local regulation relevant to pressure vessels.

5.2.1.4.1. Liquid level

A device for checking the liquid level, preferably during service, with indication of minimum

and maximum limits permissible for correct operation, shall be provided.

NOTE: This is not applicable to dash-pots.

5.2.1.4.2. Liquid quality

Liquids for use in switchgear and controlgear shall comply with the instructions of the

manufacturer.

For oil-filled switchgear and controlgear, new insulating oil shall comply with IEC 60296.

NOTE: For sealed pressure systems, instructions for maintaining the liquid quality are not applicable.

5.2.1.5. Requirements for gases in switchgear and control gear

The manufacturer shall specify the type and the required quantity, quality and density of the gas

to be used in switchgear and controlgear and provide the user with necessary instructions for

renewing the gas and maintaining its required quantity and quality except for sealed pressure

systems.

For sulphur hexafluoride (SF6) filled switchgear and controlgear, SF6 in accordance with

either IEC 60376 or IEC 60480 can be used. In order to prevent condensation, the maximum

allowable moisture content within gas-filled switchgear and controlgear filled with gas at the

rated filling density for insulation ρre shall be such that the dew-point is not higher than −5 °C

for a measurement at 20 °C. Adequate correction shall be made for measurement made at other

19

temperatures. For the measurement and determination of the dew-point, refer to IEC

60376 and IEC 60480.

Parts of high-voltage switchgear and controlgear housing compressed gas shall comply with the

requirements laid down in the relevant IEC standards.

NOTE - For checking of sulphur hexafluoride in service, refer to IEC 60480.

5.2.1.6. Auxiliary and control equipment

Auxiliary and control equipment is considered to be of conventional or non-conventional

(electronic) design components. For non-conventional design components refer to IEC

62063.

For electronic devices, electro-magnetic (EM) susceptibility shall be considered.

5.2.1.6.1 Enclosures

5.2.1.6.1.1 General

The enclosures for low-voltage control and auxiliary circuits shall be constructed of materials

capable of withstanding the mechanical, electrical and thermal stresses, as well as the effects of

humidity which are likely to be encountered in normal service.

5.2.1.6.1.2 Protection against corrosion

Protection against corrosion shall be ensured by the use of suitable materials or by the

application of suitable protective coatings to the exposed surfaces, taking into account the

intended conditions of use in accordance with the service conditions stated in Clause 5.2.1.

5.2.1.6.1.3 Degrees of protection

The degree of protection provided by an enclosure for low-voltage auxiliary and control

circuits shall be in accordance with 5.13.

Openings in cable entries, cover plates, etc. shall be so designed that, when the cables are

properly installed, the stated degree of protection of an enclosure for low-voltage auxiliary and

control circuits, as defined in 5.13, shall be obtained. A means of entry, suitable for the

application stated by the manufacturer, should be selected.

Any ventilation openings shall be shielded or arranged so that the same degree of protection as

that specified for the enclosure is obtained.

5.2.1.6.1.4 Protection against electric shock

5.2.1.6.1.4.1 Protection by segregation of auxiliary and control circuits from the main

circuit

Auxiliary and control equipment which is installed on the frame of switching devices shall be

suitably protected against disruptive discharge from the main circuit.

20

The wiring of auxiliary and control circuits, with the exception of short lengths of wire at

terminals of instrument transformers, tripping coils, auxiliary contacts, etc. shall be either

segregated from the main circuit by earthed metallic partitions (for example, tubes) or

separated by partitions (for example, tubes) made of insulating material.

5.2.1.6.1.4.2 Accessibility

Auxiliary and control equipment to which access is required during service shall be accessible

without the need to compromise clearances to hazardous parts.

Where clearances may be compromised by environmental related changes in the service access

level (for example accumulation of snow, sand, etc.) the use of increased clearances should be

considered.

5.2.1.6.1.5 Fire hazard

5.2.1.6.1.5.1 General

As the risk of fire is present in auxiliary and control circuits, the likelihood of fire shall be

reduced under conditions of normal use and even in the event of malfunction or failure.

The first objective is to prevent ignition due to an electrically energized part of auxiliary and

control circuits. The second objective is to limit the fire impact, if fire or ignition occurs inside

the enclosure.

5.2.1.6.1.5.2 Components and circuit design

In normal operation, heat dissipation of components is generally small. However, a

component may, when faulty or in an overload condition resulting from an external fault,

generate excess heat such that fire may be initiated.

The manufacturer should design or choose components taking into account normal conditions

and self-ignition characteristics due to the effects of the maximum fault power. Special

attention should be given to resistors.

Consideration should be given to the assembly of components and the relative arrangement of

those that may dissipate excessive heat by providing around them sufficient space and/or

ventilation.

5.2.1.6.1.5.3 Managing fire impact

Provisions should be taken in order to manage fire impact. Enclosures should be constructed,

insulated, made watertight, etc. with materials sufficiently resistant to probable ignition and heat

sources situated within. The manufacturer should consider that, if it ignites, a component may

emit melted flaming material and/or glowing particles.

5.2.1.6.1.6 Components installed in enclosures

5.2.1.6.1.6.1 Selection of components

21

Components installed in enclosures shall comply with the requirements of the relevant

IEC standards where applicable. Where an IEC standard does not exist the component should be

qualified with reference to another standard (issued by a country or another organization).

All components used in the auxiliary and control circuits shall be designed or selected to be

operational with their rated characteristics over the whole actual service conditions inside

auxiliary and control circuits enclosures. These internal conditions can differ from the external

service conditions specified in Clause 5.2.1.

Suitable precautions (insulation, heating, ventilation, etc) should be taken to ensure that those

service conditions essential for proper functioning are maintained, for example, heaters to

maintain the required minimum temperature for the correct operation of relays, contactors, low-

voltage switches, meters, operation counters, push-buttons, etc. according to the relevant

specifications.

The loss of those precaution means should not cause failures of the components nor

untimely operation of switchgear and controlgear. The operation of switchgear and

controlgear shall be possible during 2 h after the loss of those means. After this period, non-

operation of the switchgear and controlgear with its associated auxiliary and control circuit is

acceptable provided that the functionality resets to its original characteristics when

environmental conditions inside the enclosure for auxiliary and control circuits are back to the

specified service conditions.

Where heating is essential for correct functioning of the equipment, monitoring of the heating

circuit shall be provided.

In the case of switchgear and controlgear designed for outdoor installation, suitable

arrangements (ventilation and/or internal heating, etc.) shall be made to prevent harmful

condensation in low-voltage control and auxiliary circuits enclosures.

Polarity reversal at the interfacing point shall not damage auxiliary and control circuits.

5.2.1.6.1.6.2 Installation of components

Components shall be installed in accordance with the instructions of their manufacturer.

5.2.1.6.1.6.3 Accessibility

Closing and opening actuators and emergency shut-down system actuators should be located

between 0.4 m and 2 m above servicing level. Other actuators should be located at such a height

that they can be easily operated, and indicating devices should be located at such a height that

they can be easily readable.

Structure-mounted or floor-mounted enclosures for low-voltage auxiliary and control circuits

should be installed at such a height, with respect to the servicing level, that the above

requirements for accessibility, operating and reading heights are met.

22

Components in enclosures should be so arranged as to be accessible for mounting, wiring,

maintenance and replacement. W here a component may need adjustment during its service life;

easy access should be considered without danger of electrical shock.

5.2.1.6.1.6.4 Identification

Identification of components installed in enclosures is the responsibility of the manufacturer and

it shall be in agreement with the indication on the wiring diagrams and drawings. If a

component is of the plug-in type, an identifying mark should be placed on the component and

on the fixed part where the component plugs in.

W here mixing of components or voltages could cause confusion, consideration should be

given to more explicit marking.

5.2.1.6.1.6.5 Requirements for auxiliary and control circuit components

The auxiliary and control circuit components shall comply with applicable IEC standards if one

exists. Annex D is provided as a quick reference to many of the component standards.

5.2.1.6.1.6.5.1 Cables and wiring

The specification of cables to connect auxiliary and control circuits of the switchgear and

controlgear is the responsibility of the manufacturer. The choice is governed by the current that

must be carried, by the voltage drop and the current transformer burden, by the

mechanical stresses to which the cable is subjected and by the type of insulation. The choice of

conductors in enclosures is also the responsibility of the manufacturer.

Where a facility for external wiring is required, an appropriate connecting device shall be

provided for example terminal blocks, plug-in terminations, etc.

Cables between two terminal blocks shall have no intermediate splices or soldered joints.

Connections shall be made at fixed terminals.

Insulated conductors shall be adequately supported and shall not rest against sharp edges. W ire

routing should take into account the proximity of heating elements.

The available wiring space shall permit spreading of the cores of multi-core cables and the

proper termination of the conductors. The conductors shall not be subjected to stresses that

reduce their normal life.

Conductors connected to apparatus and indicating devices in covers or doors shall be so

installed that no mechanical damage can occur to the conductors as a result of movement of

these covers or doors.

The number of connections made to a terminal shall not exceed its designed maximum.

The method and extent of identification of conductors, for example by numbers, colours or

symbols, is the responsibility of the manufacturer. Identification of conductors shall be in

agreement with the wiring diagrams and drawings, and the specification of the user, if

23

applicable. This identification may be limited to the ends of the conductors. W here

appropriate, identification of wiring according to IEC 60445 may be applied.

5.2.1.6.1.6.5.2 Terminals

Terminals shall maintain the necessary contact pressure, corresponding to the current rating and

the short-circuit current of circuits.

Terminal blocks for wiring components inside the enclosure shall be chosen according to the

cross-section of the conductors used.

If facilities are provided for connecting incoming and outgoing neutral, protective and PEN

conductors, they shall be situated in the vicinity of the associated phase conductor terminal.

5.2.1.6.1.6.5.3 Auxiliary switches

Auxiliary switches shall be suitable for the number of electrical and mechanical operating

cycles specified for the switching device.

Auxiliary switches, which are operated in conjunction with the main contacts, shall be

positively driven in both directions. However, a set of two one-way positively driven auxiliary

contacts (one for each direction) can be used.

5.2.1.6.1.6.5.4 Auxiliary and control contacts

Auxiliary and control contacts shall be suitable for their intended duty in terms of

environmental conditions (refer to 5.4.3.1), making and breaking capacity and timing of the

operation of the auxiliary and control contacts in relation to the operation of the main

equipment.

Auxiliary and control contacts shall be suitable for the number of electrical and mechanical

operating cycles specified for the switching device.

Where an auxiliary contact is made available to the user, the technical documents provided by

the manufacturer should contain information regarding the class of this contact.

The operational characteristics of the auxiliary contacts should comply with one of the classes

shown in Table 5-3.

24

Table 5-3: Auxiliary contact classes

D.c.

Class Rated

continuous current

Rated short- time withstand

current

Breaking capacity

≤48 110 V ≤ Ua ≤ 250 V

1 10 A 100 A/30 ms 440 W

2 2 A 100 A/30 ms 22 W

3 200 mA 1 A/30 ms 50 mA

NOTE 1 This table refers to auxiliary contacts [IEV 441-15-10] which are included in an auxiliary circuit and

mechanically operated by the switching device. Control contacts [IEV 441-15-09] which are included in a control

circuit of a mechanical switching device may be covered by this table.

NOTE 2 If insufficient current is flowing through the contact, oxidation may increase the resistance.

Therefore, a minimum value of current may be required for class 1 contact.

NOTE 3 In the case of the application of static contacts, the rated short-time withstand current may be reduced if

current-limiting equipment, other than fuses, is employed.

NOTE 4 For all classes, breaking capacity is based on a circuit time constant of not less than 20 ms with a relative

tolerance of ±20%.

0

NOTE 5 An auxiliary contact which complies with class 1, 2 or 3 for d.c is normally able to handle

corresponding a.c. current and voltage.

NOTE 6 Class 3 contacts are not intended to be subjected to full substation auxiliary-supply short-circuit current.

Class 1 and 2 contacts are intended to be subjected to full substation auxiliary-supply short- circuit current.

NOTE 7 Breaking current at a defined voltage value between 110 V and 250 V may be deduced from the

indicated power value for class 1 and class 2 contacts (for example, 2 A at 220 V d.c. for a class 1 contact).

5.2.1.6.1.6.5.5 Contacts other than auxiliary and control contacts

A contact other than an auxiliary or control contact is a contact driven by a component (relay,

contactor, low-voltage switch, etc.) used in the auxiliary and control circuits.

Where a contact other than an auxiliary or control contact is made available to the user, the

technical documents provided by the manufacturer should include the rated continuous

current and making and breaking capacity of this contact. The user is responsible for

ensuring that the contact performance is adequate for the task.

The number of contacts provided shall be specified to the manufacturer in accordance with

Clause 9 or the relevant equipment standard.

5.2.1.6.1.6.5.6 Relays

Where a relay is chosen and used at a voltage different from the rated voltage of auxiliary and

control circuits, an appropriate device shall be provided to allow it to operate correctly under the

conditions specified in 4.8 (for example, provision of a series resistor).

5.2.1.6.1.6.5.7 Shunt releases

25

Shunt releases are designed for specific purposes. As no IEC standard exists for shunt releases,

they should satisfy the requirements of the relevant equipment standard.

The electrical power of the shunt releases shall be stated by the manufacturer.

5.2.1.6.1.6.5.8 Heating elements

All heating elements shall be of the non-exposed type. Heaters shall be situated so that they do

not cause any deterioration in the wiring or in the operation of the components.

W here contact with a heater or shield can occur accidentally, the surface temperature shall not

exceed the temperature-rise limits for accessible parts which need not be touched in normal

operation, as specified in Table 3.

5.2.1.6.1.6.5.9 Operation counters

Operation counters shall be suitable for their intended duty in terms of environmental

conditions and for the number of electrical and mechanical operating cycles specified for the

switching devices.

5.2.1.6.1.6.5.10 Illumination

In some enclosures, for example enclosures containing manual operating means (handles, push-

buttons, etc.), lighting should be considered. W here lighting is installed, consideration should

be given to the heat and electromagnetic disturbance produced by the lighting on the auxiliary

and control-circuit components.

5.2.1.6.1.6.5.11 5.4.4.5.11 Coils

Coils not covered by a component standard shall be suitable for their intended duty (for

example, with respect to temperature rise, dielectric withstand, etc.).

5.2.1.7. Dependent power closing

A switching device arranged for dependent power operation with external energy supply shall

be capable of making and/or breaking its rated short-circuit current (if any) when the voltage or

the pressure of the power supply of the operating device is at the lower of the limits

specified under clauses 5.2.2.7 and 5.2.2.10 (the term "operating device" here embraces

intermediate control relays and contactors where provided). If maximum closing and opening

times are stated by the manufacturer, these shall not be exceeded.

Except for slow operation during maintenance, the main contacts shall only move under the

action of the drive mechanism and in the designed manner. The closed or open position of the

main contacts shall not change as a result of loss of the energy supply or the re-application of

the energy supply after a loss of energy, to the closing and/or opening device.

26

5.2.1.8. Stored energy closing

A switching device arranged for stored energy operation shall be capable of making and

breaking all currents up to its rated values when the energy storage device is suitably

charged. If maximum closing and opening times are stated by the manufacturer, these shall not

be exceeded.

Except for slow operation during maintenance, the main contacts shall only move under the

action of the drive mechanism and in the designed manner, and not in the case of re-

application of the energy supply after a loss of energy.

A device indicating when the energy storage device is charged shall be mounted on the

switching device except in the case of an independent unlatched operation.

It shall not be possible for the moving contacts to move from one position to the other, unless

the stored energy is sufficient for satisfactory completion of the opening or closing operation.

Stored energy devices shall be able to be discharged to a safe level prior to access.

5.2.1.8.1 Energy storage in gas receivers or hydraulic accumulators

When the energy storage device is a gas receiver or hydraulic accumulator, the requirements of

5.2.1.8 apply at operating pressures between the limits specified in items a) and b).

a). External pneumatic or hydraulic supply

Unless otherwise specified by the manufacturer, the limits of the operating pressure are

85 % and 110 % of the rated pressure. These limits do not apply where receivers also

store compressed gas for interruption.

b). Compressor or pump integral with the switching device or the operating device

The limits of operating pressure shall be stated by the manufacturer.

5.2.1.8.2 Energy storage in springs (or weights)

When the energy storage device is a spring (or weight), the requirements of 5.2.1.8 apply when

the spring is charged (or the weight lifted).

5.2.1.8.3 Manual charging

If a spring (or weight) is charged by hand, the direction of motion of the handle shall be marked.

The manual charging facility shall be designed such that the handle is not driven by the

operation of the switching device.

The maximum actuating force required for manually charging a spring (or weight) shall not

exceed 250 N.

27

5.2.1.8.4 Motor charging

Motors, and their electrically operated auxiliary equipment for charging a spring (or weight) or

for driving a compressor or pump, shall operate satisfactorily between 85 % and 110 % of the

rated supply voltage (refer to 5.2.2.7), the frequency, in the case of a.c., being the rated supply

frequency (refer to 5.2.2.8).

NOTE For electric motors, the limits do not imply the use of non-standard motors but only the selection of

a motor which at these values provides the necessary effort, and the rated voltage of the motor need not

coincide with the rated supply voltage of the closing device.

5.2.1.8.5 Energy storage in capacitors

When the energy store is a charged capacitor, the requirements of 5.2.1.8 apply when

the capacitor is charged.

5.2.1.9. Operating of releases

The operation limits of releases shall be as follows:

5.2.1.9.1 Shunt closing release

A shunt closing release shall operate correctly between 85 % and 110 % of the rated supply

voltage of the closing device (see 5.2.2.7), the frequency, in the case of a.c., being the rated

supply frequency of the closing device (see 5.2.2.8).

5.2.1.9.2 Shunt opening release

A shunt opening release shall operate correctly under all operating conditions of the switching

device up to its rated short-circuit breaking current, and between 70 % in the case of d.c. – or 85

% in the case of a.c. – and 110 % of the rated supply voltage of the opening device (refer to

5.2.2.7), the frequency in the case of a.c being the rated supply frequency of the opening

device (see 5.2.2.8).

5.2.1.9.3 Capacitor operation of shunt releases

When, for stored energy operation of a shunt release, a rectifier-capacitor combination is

provided as an integral part of the switching device, the charge of the capacitors to be derived

from the voltage of the main circuit or the auxiliary supply, the capacitors shall retain a charge

sufficient for satisfactory operation of the release 5 s after the voltage supply has been

disconnected from the terminals of the combination and replaced by a short-circuiting link. The

voltages of the main circuit before disconnection shall be taken as the lowest voltage of the

system associated with the rated voltage of the switching device (refer to IEC 60038 for the

relation between "highest voltage for equipment" and system voltages).

5.2.1.9.4 Under-voltage release

An under-voltage release shall operate to open the switching device when the voltage at the

terminals of the release falls below 35 % of its rated voltage, even if the fall is slow and gradual.

28

On the other hand, it shall not operate the switching device when the voltage at its terminals

exceeds 70 % of its rated supply voltage.

The closing of the switching device shall be possible when the values of the voltage at the

terminals of the release are equal to or higher than 85 % of its rated voltage. Its closing shall be

impossible when the voltage at the terminals is lower than 35 % of its rated supply voltage.

5.2.1.10. Low and high pressure interlocking devices

All vacuum or gas filled switchgear shall be fitted with a pressure gauge. The operating pressure

shall be indicated in both Bars and MPa and clearly Visible. The pressure gauge shall have

contacts for Low pressure alarm, Lockout and spare contacts.

The switchgear shall be fitted with both visible and audible low pressure alarms. In case of a

breaker, the breaker shall be wired in such a way that gas pressure below the low pressure set

point shall render the breaker inoperational or into lockout mode. In such a state, the breaker

will maintain the initial position until the anomaly is corrected. The lockout alarm shall also be

both visible and audible.

The breaker shall also be fitted with both audible and visible alarms for pressure above

manufacturer‟s maximum recommended limits. In case of loss of vacuum the breaker shall be

rendered inoperational or into lockout mode.

Values for pressure points shall be as specified by the manufacturer of the switchgear corrected

to 20ºCelsius and the switchgear shall be filled with gas not exceeding the manufacturer‟s

recommendation. All parts in direct contact with the gas such as pipes, flanges, seals and others

shall be of material that is non-reactive to the gas.

5.2.1.11. Nameplates

Switchgear and controlgear and their operating devices shall be provided with nameplates which

contain the necessary information such as the name or mark of the manufacturer, the year of

manufacture, the manufacturer's type designation, the serial number or equivalent, the rated

characteristics etc. as specified in the relevant IEC standards.

If applicable, the type and mass of insulating fluid shall be noted on the nameplate.

NOTE It should be stated whether pressures (or densities) are absolute or relative values.

For outdoor switchgear and controlgear, the nameplates and their methods of attachment shall

be weather-proof and corrosion-proof.

If the switchgear and controlgear consist of several poles with independent operating

mechanisms, each pole shall be provided with a nameplate.

For an operating device combined with a switching device, it may be sufficient to use only one

combined nameplate.

Technical characteristics on nameplates and/or in documents which are common to several

kinds of high-voltage switchgear and controlgear shall be represented by the same symbols.

29

Such characteristics and their symbols are:

rated voltage Ur

rated lightning impulse withstand voltage Up

rated switching impulse withstand voltage Us

rated power-frequency withstand voltage Ud

rated normal current Ir

rated short-time withstand current Ik

rated peak withstand current Ip

rated frequency Fr

rated duration of short circuit Tk

rated auxiliary voltage Ua

rated filling pressure (density) for insulation pre (ρre)

rated filling pressure (density) for operation prm (ρrm)

alarm pressure (density) for insulation pae (ρae)

alarm pressure (density) for operation pam (ρam)

minimum functional pressure (density) for insulation pme (ρme)

minimum functional pressure (density) for operation pmm (ρmm)

Metal-enclosed switchgear and control gear, all their components and operating devices shall

be provided with durable and clearly legible nameplates which shall contain the following

information:

a). Manufacturer‟s name or trade mark;

b). Type designation or serial number;

c). Applicable rated values;

d). Number of the relevant standard.

The nameplates of each functional unit shall be legible during normal service. The removable

parts, if any, shall have a separate nameplate with the data relating to the functional units

they belong to, but this nameplate need only be legible when the removable part is in the

removed position.

5.2.1.12. Protection of persons against approach to live parts

The degree of protection shall be specified separately for the enclosure and for partitions. For

cubicle switchgear and control gear, it is only necessary to specify the degree of protection for

the enclosure. For main circuits of gas-filed compartments, no degree of protection needs to be

specified. The degree of protection against contact of persons with live parts of auxiliary

circuits and with any moving parts (other than smooth rotating shafts and moving linkages) shall

be indicated by means of the designation specified in Table 5-4.

30

The characteristic numeral indicates the degree of protection provided by the enclosure with

respect to persons, also to the equipment inside the enclosure.

Table 5-4 gives details of objects which will be “excluded” from the enclosure for each of the

degrees of protection. The term “excluded” implies that a part of the body or an object held

by a person, either will not enter the enclosure or, if it enters, that adequate clearance will be

maintained and no moving part will be touched. Degree of Protection against approach to live

parts and contact with moving parts protection

Table 5-4: Degrees of protection against solid foreign objects indicated by the first characteristic

Numeral

Degree of Protection Protection against approach to live parts and contact with moving

parts

IP2X By fingers or similar objects of diameter greater than 12mm

IP3X By tools, wires, etc., of diameter or thickness greater than 2.5mm

IP4X By wires of diameter or strips of thickness greater than 1.0mm

NOTE – the designation of the degree of protection corresponds to IEC 60529

5.2.1.13. Internal fault

Failure within the enclosure of metal-enclosed switchgear and control gear due either to a defect

or an exceptional service condition or mal-operation may initiate an internal arc. There is little

probability of such an event occurring in constructions which satisfy the requirements of this

standard, but it cannot be completely disregarded. Such an event may lead to the risk of injury,

if persons are present, but with an even lower probability. It is desirable that the highest

possible degree of protection to persons should be provided. The principal objective should be

to avoid such error or to limit their duration and consequences. Experience has shown that faults

are more likely to occur in some locations inside an enclosure than in others, so special attention

should be paid to these.

5.2.1.14. Enclosure

Enclosures shall be metallic. When the metal-enclosed switchgear and control gear is installed,

the enclosure shall provide at least the degree of protection specified in table 1. It shall also

assure protection in accordance with the following conditions: The floor surface, even if not

metallic, may be considered as part of the enclosure. The measures to be taken in order to obtain

the degree of protection provided by floor surfaces shall be subject to an agreement between

manufacturer and user. The walls of a room shall not be considered as parts of the enclosure.

Gas-filled compartments shall be capable of withstanding the normal and transient pressures to

which they are subjected in service. While these compartments are permanently pressurized

in service they are subjected to particular conditions of service which distinguish them from

compressed air receivers and similar storage vessels. These conditions are:

- gas-filled compartments enclose the main circuit not only to prevent hazardous approach to

31

live or moving parts but are so shaped that, when at or above the minimum functional

pressure they ensure that the rated insulation level for the equipment is achieved (electrical

rather than mechanical considerations predominate in determining the shape and materials

employed); gas-filled compartments shall be filled with a non-corrosive gas, thoroughly

dried, stable and inert.

5.2.1.15. Inspection windows

Inspection windows shall provide at least the degree of protection specified for the enclosure.

They shall be covered by a transparent sheet of mechanical-strength comparable to that of the

enclosure. Precautions shall be taken to prevent the formation of dangerous electrostatic

charges, either by clearance or by electrostatic shielding (for example a suitable earthed Wire-

mesh on the inside of the window). The insulation between live parts of the main circuit and

the inspection windows shall withstand the test voltages specified in Sub-clause 4.2.1 of IEC

62271-1 for voltage tests to earth and between poles.

5.2.1.16. Ventilating openings, vent outlets

Ventilating openings and vent outlets shall be so arranged or shielded that the same degree of

protection as that specified for the enclosure is obtained. Such openings may make use of wire

mesh or the like provided that it is of suitable mechanical strength. Ventilating openings and

vent outlets shall be arranged in such a way that gas or vapour escaping under pressure does not

endanger the operator.

5.2.1.17. Partitions and shutters

Partitions and shutters shall provide at least the degree of protection specified in Partitions and

shutters made of insulating material shall meet the following requirements

a). The insulation between live parts of the main circuit and the accessible surface of

insulating partitions and shutters shall withstand the test voltages specified in Sub-

clause 4.2.1 of IEC 62271-1 for voltage tests to earth and between poles;

b). Apart from mechanical strength, the insulating material shall withstand likewise the test

voltages specified in Item a), The appropriate test-methods given in IEC 60243-1

should be applied;

c). The insulation between live parts of the main circuit and the inner surface of insulating

partitions and shutters facing these shall withstand at least 150 % of the rated

voltage of the equipment;

5.2.1.18. Partitions

Partitions of metal-clad switchgear and control gear shall be metallic and earthed. Partitions of

compartmented and cubicle switchgear and control gear may be non-metallic. If partitions

become part of the enclosure with the removable part in any of these positions, they shall be

metallic, earthed and provide the degree of protection specified for the enclosure. Partitions

between two gas-filled compartments or between a gas-filled compartment and another

compartment may be of insulating material provided they do not become part of the enclosure

but are not intended by themselves to provide electrical safety of personnel, for which other

32

means such as earthing of the equipment may be necessary; they shall, however, provide

mechanical safety against the normal gas pressure still present in the adjacent compartment.

5.2.1.19. Pressure relief of gas-filled compartments

Where pressure relief devices are provided, they shall be arranged so as to minimize the danger

to an operator during the time that he is performing his normal operating duties if gases or

vapours are escaping under pressure. In certain designs pressure relief may be achieved by

allowing the arc to burn through the enclosure at designated points. Where such means are

employed, the resultant hole is deemed to be a pressure relief device.

5.2.1.20. Disconnections and earthing switches

The devices for ensuring the isolating distance between the high-voltage conductors are

considered to be disconnections which shall comply with IEC 60129, except for mechanical

operation tests

The requirement that it shall be possible to know the operating position of the disconnector or

earthing switch is met if one of the following conditions is fulfilled:

i). The isolating distance is visible;

ii). The position of the withdrawable part in relation to the fixed part is clearly visible and

the positions corresponding to full connection and full isolation are clearly identified; the

position of the disconnector or earthing switch is indicated by a reliable indicating

device. Any removable part shall be so attached to the 'fixed part that its contacts will

not open inadvertently due to forces which may occur in service, in particular those due

to a short circuit.

5.2.1.21. Interlocks

Interlocks between different components of the equipment are provided for reasons of safety

and for convenience of operation. Visible indication shall be provided to show whether the

mechanism is locked or free. The following provisions are mandatory for main circuits:

5.2.1.21.1. Metal-enclosed switchgear and control gear -with removable parts

The withdrawal or engagement of a circuit-breaker, switch or contactor shall be impossible

unless it is in the open position. The operation of a circuit-breaker, switch or‟ contactor shall be

impossible unless it is in the service, disconnected, removed, test or earthing position.

It shall be impossible to close the circuit-breaker, switch or contactor in the service position

unless it is connected to the auxiliary circuit, unless it is designed to open automatically without

the use of an auxiliary circuit.

33

5.2.1.21.2. Metal-enclosed switchgear and control gear without removable parts and

provided with disconnector

Interlocks shall be provided to prevent operation of disconnector under conditions other than

those they are intended for. The operation of a disconnector shall be impossible unless the

associated circuit-breaker, switch or contactor is in the open position.

NOTE - This rule may be disregarded if it is possible to have a busbar transfer in a double busbar system without current interruption.

The operation of the circuit-breaker, switch or contactor shall be impossible unless the associated disconnector is in the closed, open or

earthing position (if provided). The provision of additional or alternative interlocks shall be subject to agreement between

manufacturer and user. The manufacturer shall give all necessary information on the character and function of interlocks. It is

recommended that earthing switches having a short-circuit making capacity less than the rated peak withstand current of the circuit

should be interlocked with the associated disconnector

5.2.3. Rating Characteristics

The ratings of metal-enclosed switchgear and control gear shall cover the following:

a). Rated voltage and number of phases;

b). Rated insulation level;

c). Rated frequency;

d). Rated normal current (for main circuits);

e). Rated short-time withstands current (for main and earthing circuits);

f). Rated peak withstand current, if applicable (for main and earthing circuits);

g). Rated duration of short circuit;‟

h). Rated values of the components forming part of the metal-enclosed switchgear and

i). Rated filling pressure (of gas-filled compartments).

NOTE: For the co-ordination of rated voltages, rated short-time withstand currents, rated peak with-

stand currents and rated normal currents of metal enclosed switchgear and control gear.

5.2.2.1. Rated voltage

The rated voltage is equal to the maximum system voltage for which the equipment is designed.

It indicates the maximum value of the "highest system voltage" of networks for which the

equipment may be used. Standard values of rated voltages are given below:

a). Range I for rated voltages 245 kV and below:

3.6 kV, 7.2 kV, 12 kV, 17.5 kV, 24 kV, 36 kV, 52 kV, 72.5 kV, 100 kV, 123 kV, 145 kV, 170

kV, 245 kV

b). Range II for rated voltages above 245 kV:

300 kV, 362 kV, 420 kV, 550 kV, 800 kV

NOTE - Components forming part of metal-enclosed switchgear and control gear may have individual values of rated voltage in

accordance with their relevant standards.

5.2.2.2. Rated insulation level

The rated insulation level of switchgear and controlgear shall be selected from the values given

in Tables 6-1. In these tables, the withstand voltage applies at the standardised reference

atmosphere (temperature (20 °C), pressure (101.3 kPa) and humidity (11 g/m3)) specified in

34

IEC 60071-1.

These withstand voltages include the altitude correction to a maximum altitude of 1 000 m

specified for the normal operating conditions. The rated withstand voltage values for lightning

impulse voltage (Up), switching impulse voltage (Us) (when applicable), and power-frequency

voltage (Ud) shall be selected without crossing the horizontal marked lines. The rated insulation

level is specified by the rated lightning impulse withstand voltage phase to earth.

For most of the rated voltages, several rated insulation levels exist to allow for application of

different performance criteria or overvoltage patterns. The choice should be made considering

the degree of exposure to fast-front and slow-front overvoltages, the type of neutral earthing of

the system and the type of overvoltage limiting devices.

The "common values" used in Tables 1a and 1b apply to phase-to-earth, between phases and

across the open switching device, if not otherwise specified in this standard. The withstand

voltage values "across the isolating distance" are valid only for the switching devices where the

clearance between open contacts is designed to meet the functional requirements specified for

disconnectors.

Table 5-5: Rated Insulation levels for rated voltages of Range I

Rated voltage

Ur

kV (r.m.s. value)

Rated short-duration power-

frequency withstand voltage

Ud

kV (r.m.s value)

Rated lightning impulse withstand voltage

Up

kV (peak value)

Common value Across the

isolating

distance

Common value Across the

isolating

distance

(1) (2) (3) (4) (5)

3.6 10 12 20 23

40 46

7.2 20 23 40 46

60 70

12 28 32 60 70

75 85

17.5 38 45 75 85

95 110

24 50 60 95 110

125 145

36 70 80 145 165

170 195

52 95 110 250 290

72.5 140 160 325 375

100 150 175 380 440

185 210 450 520

123 185 210 450 520

230 265 550 630

35

145 230 265 550 630

275 315 650 750

170 275 315 650 750

325 375 750 860

245 360 415 850 950

395 460 950 1

050 460 530 1

050

1

200

5.2.2.3. Rated frequency (fr)

The standard values of the rated frequency are 16 2/3 Hz, 25 Hz, 50 Hz and 60 Hz.

5.2.2.4. Rated normal current and temperature rise

5.2.2.4.1. Rated normal current (Ir)

The rated normal current of switchgear and controlgear is the r.m.s value of the current which

switchgear and controlgear shall be able to carry continuously under specified conditions of use

and behavior.

Some main circuits of metal-enclosed switchgear and control gear (e.g. busbars, feeder circuits,

etc.) may not have the same value of rated normal current.

5.2.2.4.2. Temperature rise

The temperature rise of components contained in metal-enclosed switchgear and control gear

which are subject to individual specifications not covered by the scope of IEC 62271-1 shall not

exceed the temperature-rise limits permitted in the relevant IEC standard for that component.

The maximum permissible temperatures and temperature rises to be taken into account for

busbars are those specified for contacts, connections and' metal parts in contact with

insulation, as the case may be.

5.2.2.5. Rated peak withstand current

The peak current associated with the first major loop of the rated short-time withstand current

which switchgear and controlgear can carry in the closed position under prescribed conditions

of use and behaviour.

The rated peak withstand current shall be defined according to the d.c time constant which is a

system characteristic. A d.c time constant of 45 ms covers the majority of cases and

corresponds to a rated peak withstand current equal to 2.5 times the rated short-time

withstand current for a rated frequency of 50 Hz and below it, and for a rated frequency of 60

Hz it is equal to 2.6 times the rated short-time withstand current.

For some applications, system characteristics are such that the d.c. time constant is higher than

45 ms. Other values generally suitable for special systems are 60 ms, 75 ms and 120 ms

depending on the rated voltage. For those cases, the preferred value is 2.7 times the rated short-

time withstand current.

36

NOTE - In principle, the rated short-time withstand current and the rated peak withstand current of a

main circuit cannot exceed the corresponding rated values of the weakest of its series connected

components. However, for each circuit or compartment, advantage may be taken of apparatus limiting

the short-circuit current, such as current-limiting fuses, reactors, etc.

5.2.2.6. Rated duration of short circuit

The intervals of time for which switchgear and controlgear can carry, in the closed position, a

current equal to its rated short-time withstand current.

The standard value of rated duration of short circuit is 1 s.

If it is necessary, a value lower or higher than 1 s may be chosen. The recommended values are

0.5 s, 2 s and 3 s.

5.2.2.7. Rated supply voltage of closing and opening devices and auxiliary circuits

5.2.2.7.1. General

The supply voltage of closing and opening devices and auxiliary and control circuits shall be

understood to mean the voltage measured at the circuit terminals of the apparatus itself

during its operation, including, if necessary, the auxiliary resistors or accessories supplied or

required by the manufacturer to be installed in series with it, but not including the conductors

for the connection to the electricity supply.

NOTE The supply system should preferably be referenced to earth (i.e. not completely floating) in order to

avoid the accumulation of dangerous static voltages. The location of the earthing point should be defined

according to good practice.

5.2.2.7.2. Rated supply voltage (Ua)

The rated supply voltage should be selected from the standard values given in Tables 5-6

and 5-7. The values marked with an asterisk are preferred values for electronic auxiliary

equipment.

Table 5-6: Direct current voltage

Ua [V]

24

48*

60

110* or 125

Table 5-7: Alternating current voltage

Three-phase, three-wire or Single-phase, three-wire Single-phase, two-wire

37

four- wire systems

[V]

systems

[V]

systems

[V]

–

120/208

(220/380)

230/400*

(240/415)

277/480

347/600

120/240

–

–

–

–

–

–

120

120

(220)

230*

(240)

277

347 NOTE 1 The lower values in the first column of this table are voltages to neutral and the higher values are voltages

between phases. The lower value in the second column is the voltage to neutral and the higher value is the voltage

between lines. NOTE 2 The value 230/400 V indicated in this table should be, in the future, the only IEC standard voltage and

its adoption is recommended in new systems. The voltage variations of existing systems

at 220/380 V and 240/415 V should be brought within the range 230/400 V ± 10 %. The reduction of this

range will be considered at a later stage of standardization.

5.2.2.7.3. Tolerances

The relative tolerance of a.c. and d.c. power supply in normal duty measured at the input of the

auxiliary equipment (electronic controls, supervision, monitoring and communication) is 85 %

to 110 %.

For supply voltages less than the minimum stated for power supply, precautions shall be

taken to prevent any damage to electronic equipment and/or unsafe operation due to its

unpredictable behaviour.

For operation of shunt-opening releases, the relative tolerance shall comply with the

requirements of 5.2.1.9

5.2.2.7.4. Ripple voltage

In the case of d.c supply, the ripple voltage, that is the peak-to-peak value of the a.c.

component of the supply voltage at the rated load, shall be limited to a value not greater than 5

% of the d.c. component. The voltage is measured at the supply terminals of the auxiliary

equipment.

5.2.2.7.5. Voltage drop and supply interruption

IEC 61000-4-29 (d.c supply voltage) and IEC 61000-4-11 (a.c supply voltage) should apply to

electrical and electronic components.

As far as supply interruptions are concerned, the system is considered to perform correctly if:

There are no false operations;

There are no false alarms or false remote signaling;

Any pending action is correctly completed, even with a short delay.

5.2.2.8. Rated supply frequency of operating devices and auxiliary circuits

The standard values of rated supply frequency are d.c or 50 Hz.

38

5.2.2.9. Rated filling pressure (of gas-filled compartments)

This shall be the pressure in bars (gauge) assigned by the manufacturer referred to atmospheric

air conditions of 20°C at which the gas-filled compartment is filled before being put into

service.

5.2.2.10. Rated pressure of compressed gas supply for controlled pressure systems

The preferred values of rated pressure (relative pressure) are:

0.5 MPa – 1 MPa – 1.6 MPa – 2 MPa – 3 MPa – 4 MPa.

5.2.4. Circuit breakers

5.2.3.1. General

Circuit-breakers for voltages above 600V shall be either SF6 or vacuum type, whereas moulded

case circuit breakers shall be used for voltages up to 600 V.

Note: Oil circuit breakers are not recommended.

5.2.3.2. Connection

The supply end connections to equipment will be at the top end and load end connections at the

bottom.

5.2.3.3. Operating Mechanisms

The circuit-breaker mechanism shall normally be motor wound spring with hand wound spring

as standby. The circuit-breaker shall be capable of closing fully and latching against its rated

making current.

In the case of designs utilising portable jacking devices, three devices per switchboard are

required subject to a minimum of one for each rating of equipment in the switchboard.

Spring operated mechanisms shall have the following additional measures:-

a). If the circuit-breaker is opened and the springs charged the circuit-breaker can be closed

and then tripped without further rewind.

b). If the circuit-breaker is closed and the springs charged there shall be sufficient energy to

trip, close and then trip the circuit-breaker without further rewind..

c). Mechanical indication shall be provided to indicate the state of the charging spring and

main contacts.

d). Motor charged mechanisms shall be provided with means for charging the springs by

hand and also a shrouded push button for releasing the springs. An electrical release coil

shall also be provided.

39

e). Under normal operation, motor recharging of the operating spring shall commence

immediately and automatically upon completion of each circuit-breaker closing

operation. The time required for spring recharging shall not exceed 3 minutes.

f). It shall not be possible to close a circuit-breaker, whilst the spring is being charged. It

shall be necessary for the spring to be fully charged and the associated charging

mechanism fully prepared for closing before it can be released to close the circuit-

breaker.

g). For SF6 circuit breakers there shall be a lock-out facility incorporated when the gas

pressure is low.

All circuit-breaker operating mechanisms shall be fitted with an electrical shunt trip release coil

and in addition a mechanical hand tripping devices. The electrical tripping and closing devices

shall be suitable for operation from a power supply as stated in this Specification and shall

operate satisfactorily over the ambient temperature range when the voltage at their terminals is

any value within the voltage range stipulated in 5.2.2.1

All operating coils for use on the d.c supply shall be connected so that failure of insulation to

earth does not cause the coil to become energised. Tripping and closing circuits shall be

provided with a fuse in each pole on each unit and shall be independent of each other and all

other circuits.

Approved positively driven mechanically operated indicating devices shall be provided to

indicate whether a circuit-breaker is in the open or closed service, isolated or earthed position.

Locking facilities with padlocks shall be provided so that the circuit-breaker can be prevented

from being closed when it is open and from being manually tripped when it is closed. These

facilities shall not require the fitting of any loose components prior to the insertion of the single

padlock required. It shall not be possible, without the aid of tools, to gain access to the tripping

toggle or any part of the mechanism which would permit defeat of the locking of the manual

trip. It shall not be possible to lock mechanically the trip mechanism so as to render inoperative

the electrical tripping.

5.2.3.4. SF6 Circuit-Breakers

Circuit-breakers employing SF6 gas as an interrupting medium shall operate on the principle of

self-generated gas pressure for arc extinction. The rate of gas leakage per annum shall be

guaranteed and shall not be greater than 1% for any compartment. Means of confirming the

existence of adequate gas density in the circuit-breakers shall be available without removing the

unit from service. The system of gas monitoring shall be temperature compensated and shall be

to the approval of the Engineer.

Suitable facilities shall be included for replenishing the volume of SF6 gas should this be

necessary due to leakage. Absorption of moisture and the decomposition products of the gas

shall be achieved by integral filters.

40

5.2.3.5. Vacuum Circuit-Breakers

Circuit-breakers employing the vacuum interruption principle shall incorporate vacuum bottles

of declared and established manufacture. Each interrupter shall be capable of individual

adjustment for correct operation and easily removed for maintenance or replacement. Full

instructions for monitoring the state of vacuum and contact life shall be provided to the approval

of the Engineer.

Vacuum bottles shall not require the addition of insulation or stress shielding to achieve the

necessary dielectric strength externally and shall not be mechanically braced by components

which may reduce the integrity of the insulation across the open gap.

Further reference is available in IEC 62271 series

5.2.3.6. Moulded case circuit breakers

This section covers single- or multi-pole moulded case circuit breakers for use in power

distribution systems, suitable for panel mounting, for rating up to 1000A, 600V, 50Hz;

a). The circuit-breakers shall comply with IEC 60947;

b). The continuous current rating, trip rating and rupturing capacity shall be as specified;

c). The contacts shall be silver alloy and shall close with a high pressure wiping action;

d). Where specified, the circuit breaker shall be capable of accommodating factory fitted

shunt trip or auxiliary contact units or similar equipment;

e). The operating handle shall provide clear indication of “ON‟”, “OFF” and “TRIP”

positions;

f). The mechanism shall be of the TRIP-FREE type preventing the unit from being held in

the ON position under overload conditions;

g). All moulded-case circuit breakers in particular installation as far as practical are to be

supplied by a single manufacturer;

h). The incoming terminals of single-pole miniature circuit breakers shall be suitable for

connection to a common busbar;

i). The circuit breaker shall have a rating plate indicating the current rating, voltage rating

and breaking capacity.

For further reference on moulded circuit breakers see IEC 60947 series.

41

5.2.5. Disconnector/Isolator

5.2.4.1. Guide to the selection of disconnector and earthing switches

5.2.4.1.1 Selection Criteria

For the selection of disconnectors and earthing switches the following conditions and

requirements at site should be considered:

a). Normal current load and overload conditions;

b). Existing fault conditions;

c). Static and dynamic terminal loads resulting from the substation design;

d). Use of rigid or flexible conductors to be connected to the disconnector or earthing switch

or to which the separated contact is mounted;

e). Environmental conditions (climate, pollution, etc.);

f). Altitude of the substation site;

g). Required operational performance (mechanical endurance);

h). Switching requirements (bus transfer current switching by disconnectors, induced

current switching by earthing switches; short-circuit making capacity of earthing

switches).

5.2.4.2. Requirements in respect of the isolating distance of disconnector

For reasons of safety, disconnectors shall be designed in such a way that no dangerous

leakage currents can pass from the terminals of one side to any of the terminals of the

other side of the disconnector. This safety requirement is met when any leakage current is led

away to earth by a reliable earth connection or when the insulation involved is effectively

protected against pollution in service.

NOTE: It is usual that the isolating gap of a disconnector is longer than the phase-to-ground insulating

distance since IEC 62271-1 specifies higher withstand test levels across the isolating distance than for the

phase-to-ground insulation.

Where a long creepage distance is required, the phase-to-ground insulation distance should

become longer than the isolating gap. For such cases, to maintain low probability of disruptive

discharge across the isolating gap, the use of protective devices such as surge arresters or rod

gaps may be necessary.

5.2.4.3. Operation of disconnectors and earthing switches - Position of the movable

contact system and its indicating and signalling devices

5.2.4.2.1. Securing of position

Disconnectors and earthing switches, including their operating mechanisms, shall be designed in

such a way that they cannot come out of their open or closed position by gravity, wind pressure,

vibrations, reasonable shocks or accidental touching of the connecting rods of their operating

system.

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Disconnectors and earthing switches shall permit temporary mechanical locking in both the

open and closed position for safety purposes (for example maintenance).

NOTE: This last requirement need not be met in the case of disconnectors or earthing switches that are

operated by means of a hook-stick.

5.2.4.2.2. Additional requirements for power-operated mechanisms

Power operated mechanisms shall also provide a manual operating facility. Connecting a hand-

operating device (for instance a hand crank) to the power-operated mechanism shall ensure safe

interruption of the control energy to the power-operated mechanism.

5.2.4.2.3. Indication and signalling of position

Indication and signaling of the closed and open position shall not take place unless the movable

contacts have reached their closed or open position, respectively: and the first paragraph of

clause 5.2.4.2.1 (securing of position) is fulfilled.

5.2.4.2.3.1. Indication of position

It shall be possible to know the operating position of the disconnector or earthing switch. For

the open position this requirement is met if one of the following conditions is fulfilled:

the isolating distance or gap is visible;

the position of each movable contact ensuring the isolating distance or gap is indicated

by a reliable visual position indicating device.

5.2.4.4. Electrical position signalling by auxiliary contacts

A common signal for all poles of a disconnector or earthing switch shall be given only if all

poles of the disconnector or earthing switch have a position in accordance with 5.2.4.2.3.

Where all poles of a disconnector or earthing switch are mechanically coupled so as to be

operable as a single unit, it is permissible to use a common position-indicating device.

5.2.4.5. Maximum force required for manual operation

The values given below also apply to maintenance and operation of normally motor-operated

disconnector and earthing switches.

NOTE: These values include ice-breaking, if applicable.

The operating height above servicing level should be agreed between manufacturer and user.

5.2.4.6. Operation requiring up to one revolution

The force needed to operate a disconnector or earthing switch requiring up to one revolution

(swing lever for example) should not exceed 250. A peak value of 450 N is accepted during a

rotation of 15° maximum.

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5.2.4.7. Dimensional tolerances

For the mounting dimensions and the dimensions of high-voltage connections as well as the

earthing connections of disconnector and earthing switches, the tolerances given in ISO 2768-1

shall apply for linear and angular dimensions.

5.2.4.8. Mechanical operating tests

Operating tests are made to ensure that the disconnector or earthing switches show the

specified operating behaviour within the specified voltage and supply pressure limits of their

operating mechanisms.

During these tests, which are performed without voltage on, or current flowing through the

main circuit, it shall be verified that the disconnector or earthing switches open and close

correctly when their operating mechanisms are energized.

The tests shall be performed according to IEC 62771-102. The mentioned test programme shall

be performed only once.

During these tests no adjustment shall be made and the operation shall be faultless. The closed

and open position shall be reached with the specified indication and signaling during each

operating cycle.

After these tests, no parts of the disconnector or earthing switch shall be damaged.

For disconnector and earthing switches with a rated voltage of 52 kV and above, the

mechanical operating routine tests may be performed on sub-assemblies.

Where mechanical routine tests are performed on separate components, they shall be

repeated at site on a complete assembled disconnector during the commissioning tests. The

same total number of operations as specified in IEC 62771-102 shall be performed.

NOTE: The mechanical operating test will not be representative for the operating conditions in the

substation when complicated linkages are used between the point of operation and the switchgear

and when the bearings are mounted to weak supports.

5.2.6. Fuses

Fuses for use in distribution systems shall be as per ZS 746 -1 and ZS 746-2.

5.3 Busbars

5.3.1. General

A busbar is a low-impedance conductor to which several electric circuits can be separately

connected.

NOTE: The term busbar does not presuppose the geometrical shape, size or dimensions of the conductor. A main busbar is a busbar

to which one or several distribution busbars and/or incoming and outgoing units can be connected. A distribution busbar is a busbar

within one section which is connected to a main busbar and from which outgoing units are supplied (see IEC 60439-1)

Three phase busbars and one neutral busbar shall be provided in accordance with SANS

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10198. At the lower end of the compartment an earth bar shall be provided to which all metal

parts of the substation are to be bonded. The neutral of the substation shall be connected to the

earth bar at one point only by means of a removable link. Provision shall be made to connect

the substation earth to the earth bar.

5.3.2. Busbars Indoor Type

5.3.2.1. Current rating

a) The maximum allowable temperature of busbars (including joints) carrying full load

current in an ambient temperature as specified shall not exceed 80°C taking into

consideration a maximum ambient temperature of 40°C in Zambia. ;

5.3.2.2. Mounting

The rating and fixing of busbars shall be designed to withstand mechanical and temperature

stresses during fault conditions.

5.3.2.3. Neutral busbar

The current density in the neutral busbar shall under the specified earth fault conditions not

exceed 200A/mm2

for a rated duration of short circuit of 1s and 125A/mm2 for a rated duration

of short circuit of 3s.

The neutral shall be terminated by an adequate terminal intended for the connection to the earth

system of the installation, refer to IEC 60298.

5.3.2.4. Street lighting busbars

The street lighting busbar shall have a cross-sectional area equal to that of a phase busbar. The

busbar shall be of standard mounting and insulated.

5.3.2.5. Busbar connections

Conductor ends will be terminated in accordance with SANS 1213.

5.3.2.6. Screws, bolts and nuts

a) All bolts and screws shall be cadmium plated yellow passivated stainless steel grade

304 to BSS standards;

b) All nuts and washers shall be electro-plated;

c) Coach screws shall be electro-plated galvanized;

d) All bolts, nuts, screws shall have ISO threads;

e) The largest possible size bolt that will fit into holes in lugs and fixing holes of equipment

shall be used;

f) Bolts shall be of sufficient length so that at least two but not more than five threads

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protrude beyond the nut.

For voltages less than 1000 V, the guidelines in the following table must be used.

5.3.3. Busbars Outdoor Type

The busbars shall consist of either stranded conductors or tubes. Stranded conductors having

hollow cores shall not be used.

Material used for busbars, busbar connections and their supports, whether insulated or

otherwise, shall not be stressed beyond two fifths of its elastic limit or its 0.1% proof stress

whichever is applicable. Satisfactory provision shall be made for expansion and contraction of

busbars connections with variation in temperature.

The maximum permissible temperature of unprotected bare busbars or busbar connections when

carrying rated current shall be 85 oC.

All busbar connections shall be kept as short and as straight as possible. The design of

connections to busbars and other equipment shall be such as to permit easy dismantling for

maintenance purposes. The busbars shall be so arranged that they may be extended in length

without difficulty.

All clamps and fittings necessary for attaching the busbars and busbar connections to either

insulated supports, together with all connectors, terminals and accessories required for attaching

the connections to the busbars, switchgear, transmission lines and power transformer bushings

shall be provided. Where dissimilar metals are connected approved bi-metal clamps shall be

provided to prevent electrochemical action or corrosion. Stranded copper connections shall be

tinned at clamping points. The open ends of all tubes shall be fitted with end caps.

Busbar supports shall be designed and constructed so that resonant vibrations are eliminated or

reduced to negligible proportions.

Overhead conductors carried by substation structures shall be erected with such sags and

tensions that the maximum loading of structures is not exceeded when the conductors, at

minimum temperature, are subjected to maximum transverse wind pressure and of fault currents

on the whole projected area. Copies of the conductor sag charts and calculations relating to the

design of tubular busbar systems shall be submitted to the Engineer for approval.

Where bolted connections are used for current carrying joints torque spanners shall be used for

tightening bolts and nuts. Also where necessary washers shall be provided under bolt heads and

nuts to spread the load and reduce the effect of compressive creep under pressure. Torque value

must be quoted on drawings.

Where current carrying surfaces of alloy connections are bolted together such surfaces shall

have the oxide film removed and shall be cleaned and de-greased. A coating of approved

jointing compound shall be applied to contact surfaces and voids before bolting. Copper-

connectors shall be tinned

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5.4 Controlgear

5.4.1 Equipment Cubicles and Ancillary Apparatus

5.4.1.1 General

All cubicles shall be manufactured from enameled sheet and protection classification at least

IP3X.

Each item of equipment mounted on each cubicle shall be positioned to allow full and easy

access to the item and to all equipment adjacent of it. All equipment shall be mounted not more

than 2 metres and not less than 500 mm from the floor.

Subject to the approval of the Engineer one cubicle may accommodate equipment associated

with two primary circuits. In this case a vertical barrier must be provided inside the cubicle to

segregate the wiring and equipment associated with each primary circuit.

If 400V connections are taken through a cubicle they shall be adequately screened or insulated

and a “400 Volts DANGER” notice shall be fixed on the outside of the cubicle.

Cubicle doors shall be hinged to lie back flat to avoid restricting access. Hinges shall be of the

lift-off type. Doors shall be secured by means of handles and locking facilities shall be

provided to the approval of the Engineer.

Each cubicle shall have an interior light fitted to illuminate all apparatus inside the cubicle

without dazzle. The interior lights in each suite of cubicles shall be controlled by a switch

complete with indicating lamp which shall be mounted prominently at one end of the suite.

All cubicles shall be complete with all necessary labels fitted to the front & back to describe the

function of the equipment which shall be approved by the Engineer.

5.4.1.2 Control switches

Control switches for electrically operated circuit-breakers shall be of the pistol grip or

discrepancy type and shall be arranged to operate clockwise when closing the circuit-breakers

and anti-clockwise when opening them. The control switches shall be so designed as to prevent

them from being operated inadvertently and where switches of the discrepancy type are used

they shall require two independent movements to effect operation. The control switch shall be

so designed that when released by the operator it shall return automatically to the “neutral”

position after having been turned to the “closed” position and shall at the same time interrupt the

supply of current to the operating mechanism of the circuit-breaker.

Switches for other apparatus shall be operated by shrouded push buttons or have handles of the

spade type, the pistol-grip type shall be reserved for circuit-breaker operation only.

Control, reversing, selector and test switches shall be so mounted, constructed and wired as to

facilitate the maintenance of contacts without the necessity for disconnecting wiring.

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5.4.1.3 Instruments

All instruments shall be of the flush mounting type, dust and moisture proof, 96mm DIN square

cases complying with IEC 60051, and shall be fitted with non-reflecting glass.

All instruments and apparatus shall be capable of carrying their full load currents without undue

heating. They shall not be damaged by the passage of fault currents within the rating of the

associated switchgear through the primaries of their corresponding instrument transformers. All

instruments and apparatus shall be back connected and all cases shall be earthed. Means shall

be provided for zero adjustment of instruments without dismantling..

All voltage circuits to instruments shall be protected by a fuse in each unearthed phase of the

circuit placed as close as practicable to the instrument transformer terminals or, where

instruments are direct-connected, as close as practicable to the main connection. All power

factor indicators shall have the star point of their current coils brought out to a separate terminal

which shall be connected to the star point of the instrument current transformer secondary

windings.

Electrical energy meters where specified shall be of static type, class 0.5s, complying with ZS

644 (ZS IEC 62053-22). They shall be 3-phase instruments with two measuring elements and

equipped with operation monitoring indicators. Where maximum demand indicator has been

specified the measuring period shall be capable being selected either 30min or 60min.

All indicating instrument scales shall be long, clearly divided and indelibly marked and the

pointers shall be of clean outline. The marking on the dials shall be restricted to the scale

marking.

In general, instrument dials should be white with black markings. Scales shall be of such

material that no peeling or discolouration will take place with age under humid tropical

conditions.

Instrument scales shall be submitted for the approval of the Engineer.

Kilowatt-hour integrating meters shall comply with the requirements of ZS 643 (ZS IEC 62053-

21) unless otherwise approved by the Engineers. Cyclometer type registers including a

minimum of five drums reading whole kWh shall be provided.

5.4.1.4 Indications and Alarms

Indicators shall operate reliably at voltages down to 80 per cent of nominal.

A trip circuit supervision scheme shall be provided for each circuit and shall be arranged to

monitor the continuity of the circuit-breaker or fault throwing switch trip coil and as much of

the associated tripping wires as possible. The scheme shall be to approval.

Annunciated alarms and indications shall be by lamps illuminating a legend and shall operate

from the battery specified. The annunciation shall be grouped, each group containing the alarms

and indications associated with the particular switchgear concerned. There shall be two push

buttons for each group of annunciation, one for “Accept” and the other for “Reset”. When an

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alarm is originated the lamp shall flash, an audible alarm shall sound and a flashing amber

beacon mounted on the substation roof shall be activated. On operation of the “Accept” key the

lamp shall cease to flash and shall give a steady illumination and the audible and visible alarms

shall cease unless already cancelled by the common cut off key.

A distinction shall be made between functions by the use of the following colours:

Red .... Trip

Amber .... Alarm

White .... Indication

The lettering should show white on a dark background or black on an illuminated background.

In the former case the amber or red shall show as a bar of approximately 3 mm below the

inscription. Where it is desired to include fire alarms in an annunciator group, the facias

surround should be coloured red.

The duration of the flash shall be such that the legend may be easily read and the speed of

flashing shall not exceed three times per second.

An alarm whose initiating device does not reset until the abnormality is remedied shall remain

illuminated until the initiating device is reset, when it shall be extinguished without the use of

the reset key.

Annunciations which arise from signals of short duration (fleeting alarms) shall not restore

when the initiating contact restores. It shall be necessary to operate the reset key to clear these.

The reset key shall not be effective until after the alarm has been accepted. If a fleeting alarm is

re-operated after acceptance but before resetting, the annunciation shall return to the flashing

condition.

The annunciation circuit shall be readily adaptable for use with a fleeting or persistent initiating

signal.

Facilities shall be provided for lamp test. The lamp test shall include a test for all spare

windows, which shall be identifiable as such under test conditions.

At each 33/11 kV substation, facilities shall also be provided to extend a common substation

alarm into a remote supervisory system.

As a minimum requirement the following signals shall initiate the audible and visible alarms at

the 33/11 kV substations.

a). Circuit-breaker tripped

b). Trip circuit failed

c). Battery charger failed

d). Low battery volts

e). Transformer gas relay operated

f). Transformer high winding temperature

g). Transformer overpressure

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h). Tap-changer relay operated

i). Transformer automatic voltage control panel VT supply failed.

5.4.1.5 Indicating lamps

Indicators shall be of the LED or type and all colours shall be to approval by the Engineer.

Filament types may be considered but not encouraged.

LED indicators shall operate at not less than 20mA and red LED indicators shall be of the high

brightness type.

The rated lamp voltage should be ten percent in excess of the auxiliary supply voltage, whether

AC or DC.

The lamp glasses shall be in standard colours (IEC 60073): red, green, blue, white and amber.

The colour is to be in the glass and not applied coating and the different coloured glasses are not

be interchangeable. Transparent synthetic materials may be used instead of glass, provided such

materials have fast colours and are completely suitable for use in tropical climates.

Normally energized indicating lamps, if employed, shall in general be energized from the

station LV AC supply. In addition, facilities shall be provided for manual changeover from the

AC supply to the station DC supply via an automatically resetting switch arranged to reset after

a time interval of approximately five minutes.

Lamps and relays incorporated in alarm facia equipment may be arranged for normal operation

from the station battery, subject to the approval of the Engineer.

Lamp test facilities shall be provided so that all lamps on one panel can be tested simultaneously

by operation of a common key. Where alarm facias are specified, all alarm and monitoring

indications, apart from CB and disconnector position indications, shall be incorporated in the

facia.

All indicating lamps and lamp holder assemblies shall be suitable for continuous operation at

the maximum site ambient temperature.

Indicating lamps and lamp holders shall be arranged so that replacement of lamps and the

cleaning of glasses and reflectors can be readily effected.

To reduce heating and fouling of the panels, lamps which are continuously alight shall have the

minimum consumption consistent with the good visibility of indications in a brightly-lit room.

Indicating lamp glasses on control and relay panels shall conform to the following standard

colour code:-

Red .... Circuit-breaker closed

Green .... Circuit-breaker open

White .... Indications normally alight

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Amber .... Alarm indications (on which an action is necessary)

5.4.1.6 Relays, fuses, links and ancillary apparatus

All relays for front of panel mounting shall be flush pattern. Where practicable the clearances

between relay stems or connecting studs shall not be less than 30 mm and in no case less than

25 mm.

Relays associated with the three phases shall be marked with the appropriate phase

identification and the fuses and links shall also be suitably labelled.

Isolating links and fuses shall be provided on each panel to facilitate the isolation of all sources

of electrical potential, to allow testing or other work to be carried out on the panel without

danger to personnel or interference with similar circuits on other panels.

All fuses and links shall be accommodated within the cubicle. Fuses and links shall be grouped

and spaced according to their function in order to facilitate identification. As an alternative to

fuses and links miniature circuit-breakers will be accepted.

Links in current transformer circuits shall be of the bolted type.

All incoming circuits in which the voltage exceeds 125 volts shall be fed through insulated fuses

and/or links, the supply being connected to the lower terminal. The contacts of the fixed portion

of the fuse or link shall be shrouded so that accidental contact with live metal cannot be made

when the moving portion is withdrawn.

Resistance boxes shall be so mounted inside the cubicle that their adjustment screws are on a

vertical and accessible face. Resistances shall be provided with stud terminals. Set screws shall

not be used.

5.4.1.7 Earthing arrangements

All control and relay panels shall have a continuous earth bar of a sectional area of not less than

75 mm2 run along the bottom of the panels, each end being connected to the main earthing

system. All metal cases of equipment on the panels shall be connected to this bar by conductors

having a sectional area not less than 2.5 mm2.

Current transformer and voltage transformer secondary circuits shall be complete in themselves

and shall be earthed at one point only through links situated in an accessible position. Each

separate link shall be suitably labelled. The links shall be of the bolted type with provision for

attaching test leads.

5.4.1.8 Auxiliary Switches

Where appropriate, each item of plant is to be equipped with all necessary auxiliary switches,

contactors and mechanisms for indication, protection, metering, control, interlocking,

supervisory and other services. All auxiliary switches are to be wired up to a terminal board on

the fixed portion of the plant, whether they are in use or not in the first instance.

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The number of switches to be provided shall be determined to cater initial installation and allow

for all anticipated future extensions.

5.4.1.9 Cable terminations

5.4.1.9.1 General

All junction boxes, terminal boxes and marshalling kiosks shall be constructed of steel. All main

equipment shall be arranged so that it is accessible from the front of the box or kiosk.

5.4.1.9.2 Outdoor Boxes and Kiosks

Outdoor boxes and kiosks shall have domed or sloping roofs and the enclosure shall be of IP54

protection classification with adequate ventilation and draining facilities. They shall be so

designed that condensation does not affect the insulation of the apparatus, the terminal boards or

the cables. Where necessary, heaters shall be provided. Where these exceed 40 watts, they

shall be controlled by means of a switch mounted on the outside of the box or kiosk.

Any divisions between compartments inside the boxes or kiosks shall be perforated to assist the

natural air circulation.

If the width of the box necessitates the provision of two hinged front covers they shall close on

to a centre post which shall be removable to facilitate cable termination. The depth of the outer

case shall be not less than 200 mm unless otherwise approved.

The outer cases shall be treated before painting to prevent corrosion and shall be finished in

glossy enamel to colour approved by the Engineer.

Access shall be provided at both the front and back of kiosks and junction boxes except for

small terminal boxes of the type normally employed for wall mounting.

Doors and access covers shall be easily opened and shall not be secured by nuts and bolts.

Doors and covers under 14 kg in weight may be of the slide-on pattern; above this weight they

shall preferably be hinged.

Kiosk doors shall be fastened with integral handles. Nuts, bolts or carriage keys shall not be

used. Provision shall be made for padlocking each door.

5.4.1.10 Terminal boards

All terminals boards shall be mounted in accessible position and, when in enclosed cubicles, are

preferably to be inclined towards the door. Spacing of adjacent terminal boards shall be not less

than 100 mm and the bottom of each board shall be not less than 200 mm above the incoming

cable gland plate.

Separate terminations shall be provided on terminal boards for the cores of incoming and

outgoing cables including all spare cores. Not more than two cores may be connected to any one

terminal. Where bridging connections are necessary, these shall be incorporated in the terminal

boards.

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For terminations modular terminals, Weidmueller type (or approved equivalent) SAK 2.5/35 or

SAK 4/35 (the latter for CT circuits) shall be provided. Current transformers shall be connected

in two parallel terminations in the way that test instrument can be connected in the CT circuit

without a need to short circuit that particular CT.

10 percent spare terminals shall be provided

400/230 V circuit terminals shall be segregated from other terminals and shall be fitted with

non-flammable plastic covers to prevent contact with any live parts. They shall have warning

labels, with red lettering, mounted thereon in a conspicuous position.

5.4.1.11 Cable Entry

All cables shall enter boxes and kiosks at the base via removable gland plates.

Conduits shall not be run at or below ground level but shall wherever practicable enter boxes or

kiosks near the base.

Plates for supporting cable glands shall be at least 450 mm above ground level. Means shall be

provided to drain water off the surface of the gland plate. The back, sides and front of the box

or kiosk shall project at least 50 mm below the gland plate to prevent moisture draining on to

the plate and cable glands.

5.4.1.12 Small Wiring

All control and relay panel wiring, secondary control wiring in CBs, motor starters, controlgear

and the like shall be carried out in a neat and systematic manner with cable supported clear of

the panels and other surfaces at all points to obtain free circulation of air.

In all cases, the sequence of the wiring terminals shall be such that the junction between multi-

core cables and the terminals is accomplished without crossover.

For wiring inside cabinets PVC-insulated single core non-sheathed cable with single-wire

copper conductor, cross section 1.5 or 2.5 mm2, type H07V-U (GENELEC standard HD 21.S2

and IEC 227-3) shall be used. Multi-stranded flexible conductor cable shall be employed where

connections are subject to movement or vibration during shipment, operation or maintenance.

All wires shall be fitted with numbered ferules of approved type at each termination. At points

of inter-connection between wiring, where a change of numbering cannot be avoided, double

markers shall be provided. Such points shall be clearly indicated on the wiring diagram.

The markers on all wiring directly connected to circuit breaker trip coils, tripping switches, etc.,

shall be of a colour, preferably red, different from that of the remainder and marked "trip".

No wires may be teed or jointed between terminal points.

Bus wiring between control panels, etc., shall be fully insulated and completely segregated from

the main panel wiring.

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All metallic cases of instruments, control switches, relays, etc., mounted on control panels or in

cubicles shall be connected by means of copper conductors of not less than 2.5 mm2 section to

the nearest earth bar. These conductors shall have yellow/green coloured insulation.

5.4.2 Protective Relays and Associated Apparatus

5.4.2.1. General

Protective equipment shall be designed to disconnect faulty circuit with speed and certainty

without interference with healthy circuits. They shall also be so designed that when properly

applied incorrect operation of the circuit-breakers does not occur as a result of transient

phenomena not arising from a faulty condition of the section of line or plant associated with

each set of relays but which may occur during fault periods due to disturbances on the system.

The equipment owner shall be responsible for ensuring the correct operation of the protective

equipment and shall submit for approval recommended relay settings supported by design

calculations for all protective equipment being supplied.

5.4.2.2. Protective Relays

5.4.2.2.1. General

All d.c relays used for tripping shall operate when the supply voltage is reduced to not less than

60% or raised up to 120% of rated voltage.

All relays shall be capable of withstanding voltages up to 120% of rated voltage.

In order to minimise the effect of electrolytic corrosion, indicator coils and d.c. relay operating

coils shall be so placed in the circuit that they are not connected to the positive pole of the

battery except through contacts which are normally open.

5.4.2.2.2. Protection Settings

Unless otherwise specified the equipment owner shall calculate maximum and minimum short

circuit currents in faults at all substation buses. Based on the results of these calculations the

Equipment owner shall prepare a table of all settings for relays in those substations which

belong to the scope of the particular Contract. This table of settings shall be submitted to the

Engineer and Employer for approval prior to commissioning of any plant.

The Equipment owners shall co-operate closely in determining relay settings.

5.4.2.2.3. Form of Relays

All relays shall be contained in dustproof cases. Relays shall be of solid state type and shall be

drawout pattern, modular construction for flush mounting in standard racks. All metal bases and

frames of relays shall be earthed except where the latter must be insulated for special

requirements.

This specification applies particularly to stand alone relays, but relays forming part of a

comprehensive measurement/protection/ interlocking system may be proposed where overall

advantages can be offered. .

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The relays shall be so arranged that replacements can be effected quickly and with the minimum

amount of labour. Relay equipment incorporating electronic devices shall be arranged to plug

in and shall have positive means for retaining them in the service position. Equipment

incorporating telephone type relays shall have similar facilities.

All relays shall be arranged so that provided reasonable care is taken any dust which may have

collected in or upon the case shall not fall on the relay mechanism when opening the case.

Where relays are required to operate with a time delay the delaying apparatus shall not be of the

dashpot type.

5.4.2.2.4. Performance Requirements

Relays shall provide the electrical characteristics, repeatability, immunity to harmonics,

transients and interference, and environmental protection needed to ensure that system

performance can be achieved. The system performance requirements will be defined in

procurement schedules, and the relays and other components shall be designed to provide the

degree of discrimination, back-up and supply integrity required.

5.4.2.2.5. Reliability

The Tenderers shall quote the reliability for each device offered, in terms of designed mean time

to failures. This figure shall be used in evaluating the reliability of the overall system, the

requirement for which shall be defined in specifications covering system design.

5.4.2.2.6. Maintainability

Relays shall be designed to facilitate first line on-site maintenance, by provision of diagnostic

features and the facility to replace modular elements. As far as practicable any relay fault shall

be indicated by an alarm, which shall give a local indication and facility to transmit a signal on

the SCADA system. Maintenance should be possible without disturbing any wiring connections

or requiring other items of plant to be disconnected. Equipment owners shall provide details of

any special test equipment required for site or workshop maintenance and give recommended

maintenance procedures.

5.4.2.2.7. Setting

The relays shall be capable of being set to cover a range of main circuit parameters, and should

generally be selected such that setting ranges give scope for adjustment either side of the design

setting. Settings shall be effected at the relay and by a remote link if provided. Any such link

shall include a facility to give remote readings of settings. Settings shall be effected by switches

or by input of digital data; conventional potentiometers shall not be used for settings. The

settings shall be clearly indicated at the relay, either by the position of switches or by a digital

display. It shall be possible to alter settings with the relay in service. Loss of electrical supplies

to the relay shall not result in loss of settings for a period of 30 days.

5.4.2.2.8. Relay Contacts

The contacts of all relays shall be capable of making the maximum current which can occur in

the circuit which they have to control. They shall also be capable of breaking such currents

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unless provision is made for breaking the current on contacts elsewhere in the circuits. Relays

shall not be affected by mechanical shock or vibration or by external magnetic fields consistent

with the place or method of mounting. The contacts shall be capable of repeated operation

without deterioration.

Unless otherwise agreed all protective relays which initiate tripping shall have not less than two

independent pairs of contacts of which one shall operate the tripping relay or circuit-breaker trip

coil without the interposition of auxiliary contactors and without the use of reinforcing

contactors.

5.4.2.2.9. Tripping and Lock-out

Relay operations shall cause trips or lock-out of main circuits, as required by the equipment

schedules. Once initiated the trip signal shall persist until the trip circuit is interrupted by

opening of a normally open auxiliary contact on the circuit-breaker or device being tripped.

5.4.2.2.10. Indication of Operation

All relays which are connected to complete either the tripping circuit of circuit-breaker or the

coil circuit of an auxiliary tripping relay shall be provided with operation indicators.

Indication of operation of each element shall be given at the relay, and via the SCADA system.

The local indication shall be maintained for a period of 30 days if the electrical supplies to the

relay are lost. The remote indication shall be maintained for at least 500 ms, to ensure detection

by the SCADA system, and shall reset after no longer than 5 seconds.

Indicators shall also be provided on such additional relay elements as will enable the type or

phase of the fault condition to be identified. Each indicator shall be capable of being reset by

hand without opening the relay case and it shall not be possible to operate the relay when

resetting the operation indicator. Each indicator shall be designed so that it will not move

before the relay has completed its operation. Indicators shall be clearly visible from the front

when operated and concealed at all other times.

5.4.2.2.11. Indication of Protective Relay Failure

Internal relay faults shall be diagnosed and shall be indicated by a non-volatile device on the

relay. Failure shall also operate a pair of normally open contacts, which may be used either for

remote indication or for tripping, as required by the equipment schedules. Failure of any

auxiliary supply to the relay shall also be indicated on the relay and shall cause the normally

open contacts to operate. Such contacts shall be commoned to provide a single remote alarm of

protection equipment failure for each switchboard.

5.4.2.2.12. Facility for Resetting

Alarm and trip contacts shall reset automatically on removal of the signal causing the operation.

Lock-outs shall have facility for manual resetting at the relay, and for resetting via the SCADA

system when called for in the equipment schedules. Local indications of operation shall be reset

at the relay. Remote indications of operation shall reset as required in 4.7 above.

56

All relays which are of the hand reset type shall be capable of being reset without the necessity

of opening the case. It shall not be possible to operate any relay by hand without opening the

case.

5.4.2.2.13. Location of Relays

Where practicable relays shall be mounted on the door of a control compartment above the

circuit to which they apply. Where this is not practicable, relays may be fitted to separate

cubicles. The arrangement of such cubicles will be specified according to site arrangements;

they may be free standing, in which case relays should be fitted to fixed front panels with

maintenance access via rear doors, or they may be wall mounted, in which case relays shall be

fitted on hinged door panels.

5.4.2.2.14. Relay Cases

Relay cases shall be of standard height of 177 mm, complying with IEC 297, size 4U, and for

mounting on standard 483 mm racks. Covers shall be fitted and shall have provision for sealing

to prevent unauthorised access. Manual resetting and inspection of indications and settings shall

be possible with the covers in place, but any adjustment shall require removal of covers. With

covers in place the degree of enclosure of the relay shall be IP52 to BS 5490.

5.4.2.2.15. Terminals

Relay terminals shall accept ring type terminals with an M4 or larger screw fixing. Barriers

shall be provided between terminals, and voltage withstand and current rating shall be in

accordance with the circuit ratings and test values.

5.4.2.2.16. Test Blocks

Test blocks associated with each circuit breaker relay panel shall be provided to permit testing

of all functions, and shall be accessible from the front of the equipment. Test blocks shall

accept a multi-outlet test plug, which shall accept 4 mm plugs for interconnection and external

connection.

5.4.2.2.17. Tripping Arrangements

Trip circuits shall be of series seal-in type, and shall be operated from the substation batteries, at

voltages as defined in equipment schedules.

5.4.2.2.18. CT Circuits

Relay cases shall be fitted with devices to short out CT windings automatically on withdrawal

of relays, so that at no time is the CT secondary winding left open circuited.

5.4.2.2.19. Labelling and marking

All relays shall either be suitably marked or shall have a label nearby with the following

information:

a). Function of relay

b). Phase identification of the current supply

57

c). Characteristic curve where appropriate

d). Rated current and voltage of the relay coils

e). Rated making capacity of tripping contacts.

Items (a) and (b) above shall be visible from the front without removing the cover.

5.4.2.2.20. Overcurrent & Earth Fault relays

Where specified inverse definite minimum time (IDMT) overcurrent relays shall be provided for

overcurrent and earth fault protection. They shall be of static type.

Overcurrent relays shall be of the three pole type and shall be of the inverse definite minimum

time limit (IDMTL) pattern with separate adjustable time and current settings. The time/current

characteristic of all IDMTL relays shall be to BS 142 normal inverse curve.

The directional overcurrent relays shall have the appropriate technical capability to ensure

correct operation during a close three-phase fault.

Relay directional elements which are designed to be energised normally by voltage and current

when carrying any current between zero and 15 times rated current shall take up such a position

that the contacts are open when the voltage coil is not energised.

Relays should have adjustable settings for both operating current and time. The range of current

settings for phase faults shall be 50-200 per cent of rated current and the time setting adjustment

shall be 0.3 to 3 s at ten times the setting current.

Inverse time earth fault relays, where specified, shall have a range of settings from 10 to 40 %

of rated current.

5.4.2.2.21. Balanced Earth fault relays

Balanced earth-fault relays shall be instantaneous in action unless otherwise specified. The

arrangement however shall be such that the relay is stable under „transient‟ conditions.

5.4.2.2.22. Automatic Reclosing of 11& 33 kV Lines

Where specified the relay protection for 11&33kV overhead lines shall be equipped with auto-

reclose relay which shall perform high speed and delayed auto-reclose. The dead time for high

speed stage shall be adjustable from 0.1 s to 5.0 s and that for delayed stages from 5 s to 180 s.

Reclaim time shall be at least 5 s. Reclosure shall be initiated only by the earth fault relay.

5.4.2.2.23. Feeder protection with pilots

Pilot wire supervision equipment to the Engineer‟s approval shall be included at all substations

where pilot wire feeder protection is installed. The equipment shall include a supply fail relay,

an approved test feature for the pilot monitoring relay and adequate spare contacts for remote

indication.

5.4.2.2.24. Feeder protection without pilots

Feeder protective equipment without pilots shall be of a discriminative type.

58

5.4.2.3. Transformer protection

5.4.2.3.1. General

Current transformers which are used for transformer earth fault protection shall not be used for

any other purpose unless agreed by the Engineer.

5.4.2.3.2. Earth Fault Protection

Where earth fault protection having three line and one neutral current transformers is employed

on the winding of a power transformers it shall be so arranged that it does not operate with any

type of fault external to the transformer winding. To ensure compliance with this requirement

the equipment shall be so designed that the current flowing in the relay operating coil with any

type of fault having a magnitude up to the maximum figure specified shall preferably be not

more than a quarter and in no case more than one-half of the current required to operate the

relay when adjusted to the prescribed setting. The setting of the relay shall be such that it will

operate reliably with current of the following magnitudes in the primary winding of the neutral

current transformer alone:-

a). Power transformer neutral directly earthed - system voltage 72.5 kV and below - not

more than 20% of the rated current.

b). Power transformer neutral earthed through resistor or reactor - all voltages - not more

than 25% of the rated current of the resistor or reactor where this rating does not differ

greatly from the primary current rating of the current transformers. Where the prescribed

settings cannot be obtained special approval of the performance shall be obtained.

Where earth fault protection is employed for the winding of a transformer which is earthed

either directly or through an earthing device the Equipment owner shall provide and fix current

transformers in the neutral earthing connection of the winding of the power transformer. One

such current transformer in the neutral connection shall be used for the balanced earth fault

protection and wherever the neutral point of the transformer winding is not directly connected to

earth standby earth fault protection shall be obtained from a second current transformer having a

primary current rating of the standard value nearest to the rated current of the winding of the

power transformer with which the standby earth fault current transformer is associated.

5.4.2.3.3. Differential protection

Where specified Differential protection shall be of the instantaneous three winding biased

differential type capable of detecting phase and earth faults.

Separate facilities shall be provided to enable bias settings to be adjusted. The minimum

operating setting shall not be greater than 20 % of the rated full load current of the transformer.

The blocking based on the ratio of the fifth and the second harmonics shall be included in the

transformer differential relay to prevent unwanted operations. No interposing transformers shall

be needed. Numerical vector group matching shall be included.

59

The protection shall be designed to ensure stability on any transformer tap position under

maximum through fault conditions with maximum DC offset. An infinite source is to be

assumed and through fault current calculated using the transformer impedance only.

The trip coils of the circuit-breakers on the primary and secondary sides of the transformer shall

be so connected to the relays that the circuit-breakers shall operate together when the protective

gear functions. Facilities shall be retained for independent tripping by hand of either circuit-

breaker.

5.4.2.3.4. Restricted Earth Fault Protection

Where specified transformer windings and connections shall be protected by REF relay of high

impedance type with necessary protection against overvoltages.

Relays shall be stable for faults outside the protected zone and on magnetising inrush surges.

Sensitivity for solidly earthed windings shall not be greater than 60% of the winding rating, for

resistance earthed windings not greater than 20% of the resistor rating.

The rated stability limit shall not be less than the maximum current available for an external

fault. This shall be taken as 12 times the rated current of the protected winding of the power

transformer.

5.4.2.3.5. Standby earth fault

Where specified standby earth fault (SBEF) shall be provided for all earthing resistors fed from

a current transformer in the resistor earth connection.

The operating current of SBEF-relay shall be adjustable between 20 and 100 per cent of the

resistor rated current. The time delay shall be adjustable between 1 and 10 s.

5.4.2.4. Distribution Line Protection

5.4.2.4.1. Overcurrent and Earth fault protection

Where specified inverse definite minimum time (IDMT) overcurrent relays shall be provided for

overcurrent and earth fault protection.

Overcurrent relays shall be of the three pole type and shall be of the inverse definite minimum

time limit (IDMTL) pattern with separate adjustable time and current settings. The time/current

characteristic of all IDMTL relays shall be to BS 142 normal inverse curve.

The directional overcurrent relays shall have the appropriate technical capability to ensure

correct operation during a three-phase fault.

Relay directional elements which are designed to be energised normally by voltage and current

when carrying any current between zero and 15 times rated current shall take up such a position

that the contacts are open when the voltage coil is not energised.

Relays should have adjustable settings for both operating current and time. The range of current

settings for phase faults shall be 50-200 per cent of rated current and the time setting adjustment

shall be 0.3 to 3 s at ten times the setting current.

60

Inverse time earth fault relays, where specified, shall have a range of settings from 10 to 40 %

of rated current.

5.4.2.5. Fault event recorders

When specified fault event recorder or module to an existing protection (without a printer) shall

be provided. This shall store all pertinent data for the analysis of the fault by a separate

computer and printer. The module shall be equipped with a low speed data interface for the

remote data communication to be installed later.

Where a fault locator specified shall be provided which uses the inputs available from the

distance relay. The locator shall operate on the impedance to fault measuring principle.

Preference will be given to schemes with following features:

• Digital processing of fault and pre-fault data to calculate distance to fault.

• Printed display identifying faulted line, fault type and distance to fault.

5.4.2.6. Integrated Microprocessor Based Schemes

5.4.2.6.1. Measurement-Protection-Control

Microprocessor based protection relays may be offered as part of overall schemes to provide

protection, control functions and monitoring. The following items are a guide to the capabilities

required:-

• All protective functions for safety tripping and discrimination,

• Logic for interlocking and sequence operation of substation equipment and, where

applicable, for reconfiguring of circuits after protective tripping,

• Facility for interfacing to SCADA system for remote indication of circuit loading, voltage

etc.,

• Facility for remote setting and for remote indication of setting values,

• Ability to retain historical data on circuit conditions and to transmit information,

• Facility to record exact timing of events, including all protective and alarm operations,

• Ability to use historical data to amend tripping levels.

No failure of the remote link shall affect protective functions. The particular requirements and

the details of interfaces to the SCADA system will be subject to agreement with Utility.

5.4.2.7. Tripping and Control Power Supplies

5.4.2.7.1. Supply Voltage

Tripping and protective circuits shall be supplied from substation batteries and shall be at a

nominal or 110 V d.c.

5.4.2.7.2. Supply Arrangements

Two incoming supplies for tripping and protective equipment will normally be provided from

the substation battery, and provision shall be made for connection of one supply at each of the

end circuits on the switchboard, via links in each pole of the supply. A tripping supply buswire

61

shall be provided, and isolating links shall be inserted in the buswire at each bus-section switch

position on the switchboard. The protective equipment on each circuit shall be connected to the

supply via fuse links in each pole. The trip coil circuits and each protective relay shall be

separately fused. No other circuits (i.e. auxiliary closing) shall be supplied from the tripping

and protective equipment buswire.

5.4.2.7.3. Trip Circuit Supervision

Trip circuit supervision shall be provided for all the 11 and 33kV circuits Depending on the

extent of integrity required the schedules may call for any of the following types as specified in

the Bill of Quantities:-

• Trip circuit monitoring for the 11 and 33kV indoor type breakers

• Full trip circuit supervision for outdoor 33kV breakers.

The indications to the SCADA system shall be from changeover contacts, to maintain a positive

indication at all times.

5.4.3 Batteries & Battery Chargers

5.4.3.1. General

DC auxiliary power supply voltage shall be 110 V for protection tripping and closing supplies.

DC battery system shall comprise one 100% duty battery composed of independent cells. The

supply for the battery charger may be either three phase 400 V a.c or single phase 230 V a.c.

5.4.3.2. General Design Principals

5.4.3.2.1. Performance Criteria

Battery and battery charger systems must be designed for the purpose intended and to meet the

requirements of all applicable National standards. The primary role of the substation battery

system is to provide a source of energy that is independent of the primary ac supply, so that in

the event of the loss of the primary supply the substation control systems that require energy to

operate can still do so safely. The battery is required to supply the DC electrical requirements of

the substation, including SCADA, control, protection indication, communications and circuit

breaker switching operations when there is no output from the battery charger.

This may be due to a loss of AC supply to the substation or a fault in the battery charger. Under

these conditions the battery shall supply the DC loads for a minimum period of 5 hours after

which time the battery should then be able to supply trip-close-trip operations of an HV circuit

breaker which would typically restore supply to the battery charger. The 5 hour capacity allows

for ageing and a given minimum cell voltage under load at the end of discharge. There will be

nominally no remaining capacity on the battery at the end of the 5 hour period if subjected to the

given duty cycle at the end of its service life.

The absolute minimum requirement is that the battery has sufficient energy to allow the

substation to be made safe on loss of ac supply. A secondary requirement is to provide high

capacity support to the battery charger for operating high current transient loads that are beyond

62

the charger‟s capability. A substation shall comprise two battery chargers each capable of

providing 100% duty.

5.4.3.2.2. Design Criteria

The number of batteries provided, and the physical & electrical separation of these, shall be in

accordance with Section 17.2.5 (Number of Batteries). Where a 50 V DC supply is required for

substation communications systems, this shall be supplied from the 110V DC battery via a 50V

DC-DC converter or an independent 50V battery.

5.4.3.2.3. Battery Configuration

The battery cells shall be suitable for mounting on their bases. The battery cells shall not sit

directly on the ground instead shall be mounted on the none corrosive earth bonded rack. The

configuration and nominal capacity of the batteries shall be derived as follows: from a fully

charged state the batteries must be capable of meeting both Duty A and Duty B as shown in the

table below:

Battery Type Solenoid Operated Circuit

Breakers

Spring Operated Circuit

Breakers

Load Duty Duty A Duty A

Nominal capacity *200 Ah *200 Ah

Discharge Current 20 A 25 A

Discharge Time 5 hr 5 hr

Followed immediately by:

Discharge Current 150 A 35 A

Discharge Time 10 sec 10 sec

End terminal voltage not less

than:

100 V 100 V

Battery ageing factor 20% 20%

50V supply via: dc-dc converter/independent

charger unit

dc-dc

converter/independent

charger unit

Temperature operating range -1OC to 40

OC -1

OC to 40

OC

Accommodation Cabinet / Rack in separate

room

Cabinet / Rack in separate

room

Chemistry VRLA\Lead Acid\Nickel

Cadmium\ Lithium

VRLA\Lead Acid\Nickel

Cadmium\ Lithium

Cells in series 54 54

Float voltage (manufacturer

specific)

124.9 V (2.23 V / cell

typical)

124.9 V (2.23 V / cell

typical)

Boost voltage (max)

(manufacture specific)

135.0 V (2.41 V / cell

typical)

135.0 V (2.41 V / cell

typical)

63

* These are nominal capacities only - actual battery capacities are dependent on discharge

rates, final battery voltages and the type of loads to be supplied.

5.4.3.2.4. Number of Batteries

Substations with duplicated protection systems shall have dual (2) battery systems – one for

each protection system. Substations that do not have remote back-up protection systems shall

also have dual battery systems. Substations without duplicated protection systems, and which

have remote back-up protection, shall have a single (1) battery system. Where dual battery

systems are provided the batteries and associated chargers, including all associated wiring, shall

be kept physically and electrically isolated to ensure that potential problems with one system do

not affect the other. Each battery shall have a separate dedicated charger. „A‟ and „B‟ protection

systems shall be supplied by different batteries and the overall substation DC load shall be

distributed as evenly as possible between the two batteries, for example „A‟ protection and

SCADA supplied by battery 1, „B‟ protection, local control, protection, indication and

communications, etc supplied by battery 2.

5.4.3.2.5. Cell Casing

Cell casings shall be clear or translucent material fitted with safety (anti-explosion) vents.

5.4.3.2.6. Connections

All bolts, nuts, fasteners and electrical connections shall be of material that is resistant to

corrosion.

5.4.3.2.7. Cell Numbering

Battery cells shall be numbered starting from the positive terminal i.e. cell “1” for the first cell.

5.4.3.2.8. Battery Charging

Battery charging is to be strictly to the manufacturer‟s specification with no unapproved

changes to the regime.

5.4.3.2.9. Accommodation

5.4.3.2.9.1. Battery Cabinets

a). Batteries are to be accommodated in a separate ventilated room fitted with extractor fans

and fire protection systems;

b). Cabinet to be designed to facilitate front access to the batteries, with sufficient space in

front of the cabinet for lifting and carrying gear for handling individual cells;

c). Cabinet to be treated against electrolyte spill (electrolyte is gel and limited quantity, so

spread under cell rupture is limited);

d). Where multiple battery groups are provided, the batteries shall be located with sufficient

separation to enable maintenance or similar activities on one battery to not adversely

affect operation of the other;

64

5.4.3.2.9.2. Safety

a). Battery rooms shall provide easy access for batteries and battery stands. In addition,

battery rooms shall be dry, well lit, well ventilated and protected against the ingress of

dust and foreign matter.

b). Battery room shall have eye wash facilities.

c). Battery rooms shall provide for possible future expansion / refurbishment, therefore it

shall be located at the end of the building. Battery rooms shall be situated as near to the

associated loads and rectifier equipment as possible.

d). Every endeavor shall be made to ensure that the battery room is situated on the coolest

side of the building.

e). Separate battery rooms shall be provided for batteries with different types of electrolyte,

i.e. nickel cadmium and lead-acid batteries shall not be installed in the same room. Two

or more batteries with the same type of electrolyte may be installed in the same room but

on separate battery stands.

f). An access passage at least one metre wide to all battery rows and a minimum of one

metre between rows of battery stands shall be provided.

g). Only single row or stepped double row single tier battery stands may be positioned

against a wall. The step shall be such that the top of the cell plates of the back row is

exposed.

h). The minimum distance between any battery terminal and the nearest water supply point

shall be two metres.

i). Rows of battery stands shall be positioned such that they do not jeopardize or obstruct

the doorway.

j). Wherever possible the stands shall be positioned perpendicular to the entrance wall. The

battery arrangements shall comply with the layout drawing, showing the positioning of

the different batteries.

5.4.3.3. Battery Chargers

5.4.3.3.1. Type

Battery chargers shall be low ripple, UPS style switch mode charger with temperature

compensation facility.

Battery chargers shall be suitable for providing supply to a load with or without a battery

connected in parallel and are to be a suitable for wall and floor mounting. Battery chargers are

to be single-phase connected to facilitate connection of portable generator sets in situations of

loss of ac supply (such as under “black start” conditions or other loss of ac supply).

5.4.3.3.2. Location

Battery charger units shall be located within the Substation Control Room, as close as

practicable to the relevant battery.

65

5.4.3.3.3. AC Supply

For substations where two battery systems are provided, AC supply to each battery charger shall

be taken from a different auxiliary AC distribution switchboard.

5.4.3.3.4. Features

Battery chargers are to have an AC input circuit breaker, battery monitor relay, DC output fuses

or circuit breakers and output voltage indicator. The charger is to be operated in accordance

with the battery manufacturer‟s recommendations.

5.4.3.3.5. DC Supply Circuits

The positive and negative shall be in separate conduits and fused as shown in the figure.

Figure 5-1: Schematic representation of a battery charger

5.4.3.4. Battery Disposal

Disposal of all batteries shall be in accordance with the Environmental Management Act No.12

of 2011

66

5.4.4 Metering

5.4.4.1. General

The metering shall be for the purpose of measuring kVA/kVAr-hours/kWh for tariff purposes.

The metering equipment shall be static and comply with the following Zambia Standards:

a). ZS IEC 62053 61: Electricity metering equipment (a.c.) Particular requirements - Part

61: Power consumption and voltage requirements

b). ZS IEC62053 31: Electricity metering equipment (a.c.) Particular requirements - Part

31: Pulse output devices for electromechanical and electronic meters (two wires only)

c). ZS IEC 62053 23: Electricity metering equipment (a.c.) Particular requirements - Part

23: Static meters for reactive energy (classes 2 and 3)

d). ZS IEC 62053 22:2003 Electricity metering equipment (a.c.) Particular requirements -

Part 22: Static meters for active energy (classes 0.2 S and 0.5 S)

e). ZS IEC 62053 21: Electricity metering equipment (a.c.) Particular requirements Part

21: Static meters for active energy (classes 1 and 2)

f). ZS IEC 62053 11: Electricity metering equipment (a. c.) – Particular requirements - Part

11: Electromechanical meters for active energy (classes 0.5, 1 and 2)

5.4.4.2. Design

All integrating meters shall be static and shall be suitable for operating in the following

manner:-

a). Single Element Meters (2-wire).

These may be of either whole current or current transformer operated type. In either case

the voltage coil shall be suitable for a nominal voltage of 230 volt connected phase to

neutral. Such meters will be used to measure a single phase input or three single phase

meters will be combined to measure a three phase input where the load may be balanced

or otherwise.

b). Three Element Meters (4-wire).

These shall be of either the whole current or current transformer operated type and shall

be used for balanced and unbalanced three phase loads at a nominal voltage of 400/230

volt.

c). Two and Half Element Meters (4 wire)

These shall be designed to operate from current transformers in each of the three phases

and potential transformers connected between two of the phases and neutral

d). Three Element Meters (3-wire)

These shall be of either the whole current or current transformer operated type and shall

67

be used for balanced and unbalanced three phase loads at a nominal voltage of 400/231

volt

5.4.4.3. Meter Accuracy

The accuracy class or equivalent, is based on the MVA capacity of the connection and for new

installations shall as a minimum be as follows, subject to operating within the combined limits

of error set out in Table 5-8 below: -

Table 5-8: Meter accuracy

Equipment Equipment Accuracy Class

Equipment Type For connections

> 100 MVA >20-100 MVA 1 – 20 MVA < 1MVA

Meters 0.2S 0.5S 1.0 2

5.4.4.4. Meter Enclosure

Meter enclosure shall be IP 51 in accordance with IEC 60529

5.4.4.5. Labels

All meters shall be clearly and permanently labelled.

5.5 Auxiliary Equipment

Substation lighting

Recommended minimum levels of substation lighting shall be maintained at all times for the

safety and security of personnel and the facility. The substation lighting requirements can be

referred to ZS 418.

5.5.1. Fire suppression systems

The design and operation of a new or existing substation shall take recognition of the fire

hazards associated with the installations, the risks involved and the responsible person shall

provide appropriate fire-protection mitigation measures. The requirements can be referred to ZS

IEEE 979.

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6. CABLES AND CONDUCTORS

6.1. General

When cables and conductors are being selected, some of the main points to be considered are:

a). Maximum operating current;

b). Cyclic pattern of the current;

c). Voltage drop;

d). Short-circuit requirement;

e). Exposure to mechanical damage;

f). Lifetime costs, including the cost of losses;

g). Earthing requirement;

h). Current ratings, including de-rating factors;

i). Possibility of theft of cable and energy, and

j). Ability to withstand ultraviolet radiation.

For the preferred type of cable or conductor available within the ranges covered by the relevant

Zambian cable standards. The permissible short-circuit current for a cable or conductor is

determined by the maximum permissible conductor temperature and the duration of the short-

circuit current, in other words, the time from the start of the short-circuit until it is broken by

protective devices. The relevant formulas or tables and charts that list the maximum

permissible short-circuit currents for different time intervals can be obtained from the cable

manufacturers.

6.2. Fault currents and short-circuit ratings of cables

6.2.1. Fault current on the MV network

If the fault level in megavolt amperes is known, the fault current on the MV network is given

by:

3

s

f

fV

PI

(7.1)

Where

If is the fault current, in kilo amperes;

Pf is the MV fault level, in megavolt amperes;

Vs is the MV system voltage, in kilovolts.

The size of the cable can then be checked against the manufacturer‟s tables of short-circuit

ratings for the expected fault clearance time.

Example:

For an MV fault level of 250 MVA, and an 11 kV three-phase system, the fault current is:

69

kA12.13113

250

fI

(7.2)

6.2.2. Fault level at the LV terminals of the transformer

The MV fault level should be taken into account in the calculation of the LV fault current at the

transformer bushings. To allow for MV growth, use the maximum planned fault level at the

step- down MV substation or the rating of that substation‟s switchgear.

The formula for the fault level at the LV terminals is:

3101

1000

s

r

p

f

f

VT

Z

P

I

(7.3)

A simplified formula which does not take the MV fault level into account (i.e. assumes an

infinite MV bus) can be used. It gives an LV fault level around 5 % higher than when equation

7.3 is used. The simplified formula is:

3

100

sp

rf

VZ

TI (7.4)

Where;

If is the fault current, in kiloamperes;

Pf is the MV fault level, in megavolt amperes;

Zp is the transformer impedance, as a percentage;

Tr is the transformer rating, in kilovolt amperes;

Vs is the LV system voltage, in volts.

Example:

For an MV fault level of 250 MVA, an LV system voltage of 400 V and a transformer of 500

kVA and 5 % impedance, the fault current is:

kA88.13

3400500

105

250

1

1000

fI (7.5)

Using the simplified formula, the calculated fault current would be 14.43 kA.

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6.2.3. Maximum fault current at service distribution points (SDPs).

The three-phase fault level should be calculated at each node on the distributor where the cable

size changes to allow checking whether the fault current rating of the cable from the SDP will

be exceeded.

The impedance at the transformer LV terminals is mainly reactive, whereas the LV feeder

impedances have both resistive and reactive components. For reasonable accuracy, the cable

resistance and reactance both have to be taken into account.

The impedance at any point is the vector sum of the impedance up to the transformer LV

terminals plus the sum of all LV feeder impedances. The feeder impedances should be taken at

the same temperatures used for voltage drop calculations, i.e. 30 °C for underground cables and

40 °C for overhead lines and ABC.

The reactance up to the LV terminals, in ohms, referred to the LV side, is given by:

10003

s

ss

I

VX

(7.6)

Where;

Xs is the reactance up to the LV terminals, in ohms;

Is is the three-phase fault current at the LV terminals, in kilo Amperes;

Vs is the LV system voltage, in volts. If the sum of the LV feeder impedances is Rf + jXf,

then the total impedance, in ohms, is:

(7.7)

Where:

Rf: is the sum of the feeder resistances

Xf: is the sum of the feeder reactances

The three-phase fault current, in kilo amperes, is then given by:

2

2

100031000

1000

s

sff

s

t

sf

I

VXR

V

Z

VI

(7.8)

For a fault level at the transformer LV terminals of 13.88 kA (see previous example) and a total

LV feeder impedance of (0.01299 + j 0.0061) Ω, the fault current in kilo amperes would be:

2

222

10003

s

sffsfft

I

VXRXXRZ

71

82.8

100088.133

4000061.001299.010003

400

2

2

fI

(7.9)

6.2.4. Minimum fault level at ends of feeders

To ensure that fault protection devices operate successfully, the single-phase fault current at the

end of each branch and at the consumer‟s point of supply should be calculated. This is

particularly significant in long, lightly loaded LV feeders. Since these feeders are longer than

usual, their impedance Z rather than resistance only, should be used. The fault current should

be larger than 1.6 times the full load current.

6.2.5. Standardized procedure for short-circuit calculations

Methods for the calculation of short-circuit currents are given in IEC 60909-0 and other

standard texts. These methods can be applied to evaluate the maximum and the minimum short-

circuit currents, in order to correctly select and adjust protection device.

72

7. OVERHEAD DISTRIBUTION LINES

7.1 General

Overhead power lines will be selected based on the suitability for current carrying capacity,

topology of terrain, interaction with users of the area (crossing points, human proximity, mobile

machinery, agricultural machinery, wildlife and livestock), and the economic requirements.

The overhead line basically consists of the overhead lines (conductors), support structures i.e.

poles/tower, stay wires, insulators, aerial guard earth wire(s), cross arms, lightning arrestors, arc

horns, anti-climbs, red ball aviation warnings systems, catch nets, goal posts.

7.2 System Voltages

Distribution systems in Zambia use system voltages of 33kV, 11kV, 3.3kV, 0.55kV and 0.4kV.

The suitability of the system voltage is basically dependent on the choice of supply of the

distributor with respect to the length of the line, operational machinery, segregation of voltage

ranges etc.

Overhead lines may consist of similar components, however special consideration must be taken

into account with respect to the system voltage of the overhead line in line height clearance, line

to line spacing, aerial earth guard wire to line clearance, choice of insulators, fuse links, arc

horns, and lightning surge arrestors.

7.3 Conductors

7.3.1 Insulated Conductors

7.3.1.1 Aerial Bundled Cables (ABC) Voltages up to 600V

Aerial Bundled Cables are used as a preferred economic means to supply power to areas where

the property of insulation is of prominent importance such as national parks, sub-urban areas

with a large density in population and heavily built-up places with no provision for underground

cabling.

As a guide for determining the specifications for cores consisting of stranded that are insulated

with cross-linked polyethylene (XLPE) and that are intended for use in aerial bundled conductor

(ABC) systems for overhead single-phase and three-phase electricity distribution operating up

to 600/1 000 V, please make use of SANS 1418-1 and refer to IEC 60502.

As a guide for determining the requirements for assembled insulated conductor bundles, please

make use of the SANS 1418-2.

As for further standards for aerial bundled conductors, please make reference to SANS 1713

and for testing guidance and fittings, fasteners, line taps, brackets the following standards can be

used:

1. SANS 10198-14: Handling and installation of electrical aerial bundled

conductor (ABC) cables power cables of rating not exceeding 33 000V.

2. SANS 6282-1: Conductor resistance testing of electrical aerial bundled bare

and insulated conductors.

3. SANS 6282-3: Mechanical testing of electrical aerial bundled bare and

insulated conductors.

4. SANS 6101: Testing to dielectric adherence to conductor of supporting cores

of aerial bundled conductors.

73

5. SANS 6100: performance testing of mechanical and thermal stresses of

supporting cores.

7.3.1.2 Aerial Bundled Cables (ABC) voltages above 600V to 33kV

Considering the nature of the aerial bundled conductors for use up to voltages of

33kV, there supporting structure and components are mainly the same. However, for

guidance make reference:

1. SANS 10198-14: Selection, handling and installation of electrical aerial

bundled conductor (ABC) cables power cables of rating not exceeding

33,000V.

2. SANS 6282-1: Conductor resistance testing of electrical aerial bundled bare

and insulated conductors.

3. SANS 6282-3: Mechanical testing of electrical aerial bundled bare and

insulated conductors.

4. SANS 6101: Testing to dielectric adherence to conductor of supporting cores

of aerial bundled conductors.

5. SANS 6100: Performance testing of mechanical and thermal stresses of

supporting cores.

7.3.2 Bare Conductor

7.3.2.1 Aluminum Conductor, Steel Reinforced (ACSR)

Aluminium conductors with steel reinforcement shall be selected based on the standard size

suitability of current loading and mechanical withstand strength of the support structures and the

requirements of IEC 60889.

7.3.2.1.1 Maximum Limits - Reduced limits to avoid fatigue failure due to vibrations for

Aluminium Conductor, Steel Reinforced (ASCR):

If vibration dampers are not used and the lines have relatively short spans, typically under 200

m, the initial tension at -5 °C should not exceed 25 % of the ultimate tensile strength of the

conductor.

When vibration dampers are used, the following limitations are recommended:

a) The initial tension at -5 °C should not exceed 33.3 % of the ultimate tensile strength

of the conductor;

b) The initial tension at 15 °C should not exceed 2 5 % of the ultimate tensile strength

of the conductor; and

c) The final tension at 15 °C should not exceed 20 % of the ultimate tensile strength of

the conductor.

Additional dampers are not required for bundled conductors if the tension is below a

certain value 7,

proportional to the conductor weight:

T = 1 800 Mc

Where;

T is the limiting tension, in newton‟s; and

Mc is the conductor weight per metre, in newton‟s per metre.

In the case of single conductors, it is not economical to use this value to limit initial

74

tensions, and current practice is to limit the final tensions. Initial tensions are limited

by the support structure capacity on short spans.

All Aluminium Alloy Conductors (AAAC)

Aluminium conductors shall be selected based on the standard size suitability of

current loading and mechanical withstand strength of the support structures and the

requirements IEC 61089.

Maximum Limits - Reduced limits to avoid fatigue failure due to vibrations for All

Aluminum Alloy Conductor (AAAC) (Refer to Item on ASCR)

7.3.2.2 Copper Conductor

Copper conductors shall be selected based on the standard size suitability of current loading and

mechanical withstand strength of the support structures and the requirements of BS 7884.

The tension at 15 °C should not exceed 26 % of the ultimate tensile strength of the conductor.

7.3.3 Conductor Joints

All joints shall be such that their current-carrying capacity exceeds that of the conductors that

are being joined. Tension joints shall have a breaking strength of at least 95 % of that of the

conductor. In areas that are conducive to corrosion, it is good practice to coat the joined ends

and fill the fittings with chemically inert corrosion-inhibiting paste.

There shall be no joints made in either the conductors or the earth wires on a road or rail

crossing span.

7.4 Support Structures

7.4.1 Wooden Poles

The wooden poles shall comply with the specifications in the Zambian standard on wood poles

ZS 746 – 6.

7.4.2 Concrete Poles

7.4.2.1 General

Concrete poles shall be one of the following types, as specified by the purchaser and in

accordance with SANS 470:

a). Reinforced concrete pole,

b). Partially pre-stressed concrete pole, or

c). Pre-stressed concrete pole

Poles shall be manufactured in accordance with NRS 038

7.4.2.2 Design

Length, tip and butt dimension:

The overall length of the pole shall be as specified, and shall be one of the following standard

lengths: 4m, 7m, 9m, 10m, 11m, 12m, 15m, 18m, 21m and 24m. The tip and butt dimensions of

the 4m up to 11m poles shall be as per the detailed figures in NRS 038.

75

7.4.2.3 Cover of reinforcement

The minimum thickness of the overall reinforcement in the case of centrifugally spun poles shall

be not less than 15mm over the entire length of the pole. In the case where poles are

manufactured by any other process the cover shall not be less than 20mm. When poles are

required for use in aggressive soils the special additional requirements may include one or more

of the following: Protective coatings; Additional concrete cover to reinforcement; Replacement

of cement with slagment; higher factor of safety (to limit crack widths)

7.4.2.4 Finish

The finished product will have a smooth external surface free from honeycombing. All corners

shall be clean, straight and rounded to a radius of at least 5mm.

7.4.2.5 Holes

Holes shall be provided in the poles during the manufacturing of the poles. These holes shall be

used for the attachment of strain or suspension and other equipment. The holes shall be

positioned as specified in the relevant figures detailed in NRS 038. Drawings indicating the

specified poles with pole holes shall be furnished for approval prior to ordering thereof. On all

transformer poles, the integral earthing facility EW 2900 and EW 8700 shall be replaced with a

PVC conduit embedded in the concrete to protect the earth conductor in order to allow for

separate earthing of the MV and LV earth in accordance with SANS 10292 and SANS 10200

respectively. This separate earthing is necessary when the earth resistivity value of the

transformer structure is above 1 ohm. On all other MV poles the earthing ferrules (EW 2200 and

EW 8000) shall be provided for earthing of the poles.

7.4.2.6 Pole Strength

Pole strengths shall comply with Table 7-1,

Table 7-1: Standard pole lengths, minimum ultimate loads and torsional capacities

76

7.4.3 Steel Poles/Towers

11.4.3.1 Design

All steel structures shall be manufactured in accordance with industry standards and ISO

certifications in accordance with SANS 121. Steel structures shall be galvanized in order to

protect the structure from corrosion.

11.4.3.2 Paint and Finishing

Painting and finishing shall be in accordance with BS 2569 and SANS 1091. Where the

galvanized coating has been damaged during erection and after all assemblies have been

attached to the structure, zinc metal paint in accordance with BS 2569 shall be applied to the

areas for protection against corrosion.

7.4.4 Stay wires

The stay should be installed in accordance with figure below and carefully backfilled:

Figure 7-1: Stay anchor assembly installation detail

When the stay is installed, the stay wire should be made off in accordance with figure above.

Stayed poles should be so erected that they lean away from the stay position by at least half a

pole diameter at the top. This will ensure correct alignment when the stay is made off correctly.

77

When the stay wire is tensioned using the correct tensioning equipment such as a pull-lift and

come-along clamps, the stay is tensioned until the pole leans towards the stay by at least half a

pole diameter at the top.

No off-cuts of stay wire should be left on site, since these are dangerous to livestock.

7.4.5 Failure Limits of Support Structures:

Supports Damage limit Failure limit

Type Material of elements Loading mode

Lattice towers, self-

supporting or guyed

All elements, except

guys

Tension Yield (elastic) stress Ultimate (breaking)

tensile stress

Shear 90% (elastic) shear stress Shear (breaking) stress

Compression

(buckling)

Non elastic deformation

from //500 to //100 Collapse by instability

Steel guys Tension

Lowest value of:

yield stress(70% to 75

% UTS)

deformation

corresponding to 5%

reduction in tower

strength

need to readjust

tension

Ultimate tensile stress

Poles

Steel

Moments

1% of non-elastic

deformation at the top, or

elastic deformation that

impairs clearances.

Local buckling in

compression or ultimate

tensile stress in tension.

Compression

(buckling)

Non elastic deformation

from //500 to //100 Shear (breaking) stress

Wood

Moments

3% of non-elastic

deformation at the top, or

elastic deformation that

impairs clearances.

Local buckling in

compression or ultimate

tensile stress in tension.

Compression

(buckling)

Non elastic deformation

from //500 to //100

Collapse by instability

Concrete Permanent or non-

permanent loads

Crack opening after

release of loads, or 0.5%

non-elastic deformation.

Collapse of the pole

NOTE 1 The deformation of compression elements is the maximum deflection from the line joining end points. For elements

subjected to moments, it is the displacement of the free end from the vertical

NOTE 2 / is the free length of the element

NOTE 3 The width of crack for concrete poles to be agreed upon.

7.5 Insulators

7.5.1 General

Long rod, Class A insulators shall be used at all cross arms for medium voltage strain, terminal

and pole mounted transformer structures. The cycloaliphatic long rod, polymer type (silicone

rubber) and porcelain insulator shall be puncture proof and of the type as specified in design

Detail Specifications as approved by the user/utility.

The end fitted attachment shall be of the aluminium alloy clevis and tongue twisted type or

made of hot-dip galvanized forged steel or ductile cast iron, are directly attached to the glass-

fiber-reinforced plastic (FRP) core rod as in the case of silicone rubber insulators. The insulator

78

shed material shall have a high resistance to tracking by surface leakage currents and operate

normally under adverse weather conditions.

Line post type insulators shall be installed on straight line structures and the insulating material

shall be a cycloaliphatic resin, silicone rubber or porcelain complete with 20mm spindle

including nuts and washers. Line post insulators shall furthermore be of the capless, solid-core

type, be puncture proof, radio interference free and shall display superior performance in

polluted environments. They shall have a basic insulation level of either 135kV or 150kV as

specified in the Detail Specification in accordance with referenced standards. All standards

referenced at the end of this section shall be adhered to.

Glass type insulators shall where possible not be used due to vandalism. However glass

insulators can be used if the service feels it necessary and is in accordance with the relevant

international standards. Glass insulators are permitted in coastal regions up to 40 km in land

from the coastal region, due to corrosion and heavy pollution (of which silicone rubber

insulators off a great resistance to pollution effects).

7.5.2 Electrical design

Insulators together with their fittings shall comply with SANS 60305, SANS 60383, BS EN

60305, BS 3288 and IEC 61109 and shall offer a high resistance to damage, caused by

malicious vandalism. Insulator material shall be cycloalipohatic resin or polymer type such as

silicon rubber based. As an alternative high grade porcelain insulators shall be used. The

flashover and puncture voltages shall not be less than the values stated in the table below.

Insulator flashover voltage, wet and dry, shall be less than the puncture voltage. Shackle

insulators shall be used on all low voltage overhead conductors. The shackle insulators suitable

for mounting to the pole with a D-bracket shall be of the type specified in the Standard

Specification in accordance with the requirement.

7.5.3 Mechanical design

The strength of the insulator shall be such that at the maximum working load of 4kN for line

post insulators and 40kN for strain insulators shall be afforded.

7.5.4 Clamps and conductor fittings

Tension conductor clamps shall be of approved type and shall be as light as possible, and shall

be designed to avoid any possibility of deforming the stranded conductor and separating the

individual strands. All fittings shall comply with the stranded coupling dimensions specified in

the reference standards.

Intermediate pole conductor binding shall be carried out by means of wrap lock ties complete

with neoprene cover. Tension fittings shall be the preformed wire type, specially designed for

the ACSR conductor used together with suitable fittings for securing the tension insulators.

Tension insulator sets and fittings shall be of approved standards to give the minimum required

clearances between the jumper conductor and the rim of the live end insulator units. Adequate

bearing area between fittings shall be provided and “point” or “line” contacts shall be avoided.

All split pins for securing the attachment of fittings of insulator sets shall be of stainless steel

type material and shall be backed by washers. D-shackles between insulator and eye shall be

installed at all strain positions in accordance with SANS 10280.

79

7.5.5 Strain insulators

Strain insulators of the twisted clevis tongue type are required for strain and terminal poles. The

insulators shall be cycloaliphatic resin or high grade porcelain material as specified in the

detailed project specification and the approved national standards. Strain insulators shall be

complete with galvanized clevis pin (to SANS 121) c/w washer and stainless steel split pin (304

s/steel), for preformed dead end. Strain insulators shall be installed and connected to cross-arms

and A-frames, with D- shackles, clevis thimble and preformed dead end for conductor as per

design specifications.

Table 7-2: Mechanical strengths

Nominal voltage: 11kV 22kV 33kV

Impulse withstand (Minimum) 120kV 150kV 180kV

Mechanical strength (Minimum) 70kN 70kN 70kN

7.5.6 Porcelain disc insulator

High grade porcelain, 70kN mechanical strength. Nominal voltage – 11kV, 22kV or 33kV as

specified in this standard.

7.5.7 Long rod insulator:

Cycloaliphatic long rod, min. failing load 70kN, with clevis tongue twisted arrangement with

corrosion resistant end caps, complete with galvanized clevis pin (to SANS 121) c/w washer

and stainless steel split pin (304 s/steel), preformed dead end type for conductor size as

specified – nominal voltage of 11kV, 22kV or 33 kV as specified.

Silicone long rod insulators are designed to meet the highest requirements in distribution power

systems up to 72 kV. They have high lightning impulse and power frequency withstand voltages

and a long creepage class (> 31 mm/kV). Silicone long rod insulators are available with

mechanical ratings up to Specified Mechanical Load (SML) = 70 kN.

7.5.8 Intermediate insulators

Line post insulators are required for the intermediate poles on A-frames and for staggered

vertical delta configurations. Complete installed and connected to A-frame, with spindles or on

poles c/w spindles, curved washer (50 x 50), spring washer and nuts. A-frame mounting: Short

spindle – Type M2 threaded to 44mm complete with washer, nut and locknut, for mounting

bracket, complete with line tie for specified the specified conductor. Pole-mounting: long

spindle – Type M2 with 178mm shank threaded to 100mm, 250mm for mounting through pole,

c/w curved washer (50 x 50), spring washer and nut. Complete with line tie for specified

conductor.

7.5.9 Porcelain line post insulator

High grade porcelain for 11kV, 22kV or 33kV, 4kN lateral mechanical strength. Complete

installed with line ties for specified conductor.

80

7.5.10 Cycloaliphatic line post insulator

For A-frame mounting cycloaliphatic line post insulator – cantilever failing load 4kN, for M20

spindle – for 11kV and 22kV as specified

7.6 Aerial Guard Earth Wire

For high voltage lines, two longitudinal 18 to 27 mm2 galvanized steel earth wires are to be

provided with 6mm diameter galvanized steel cross lacings. The longitudinal earth wires are to

be located at a horizontal distance outside the conductors of not less than two-thirds of the

vertical distance between the lowest adjacent high voltage conductor and the aerial earth wire,

or 200mm, whichever is the greater. The aerial earth guard wire shall be so placed that all

conductors fall within the shielding angle.

7.6.1 Mechanical Strength of the aerial earth guard wire:

In the case of galvanized steel earth wires of minimum breaking strength in the range 700 MPa

to 1100 MPa, the maximum tension at 15 °C should be such that the stress in the earth wire does

not exceed 180 MPa. This criterion permits the use of tensions (at 15 °C) of the following

percentages of minimum breaking strength:

a). 700 MPa wires: 25 %; and

b). 1 100 MPa wires: 15 %.

Earth wires are often strung to match, approximately, the sag of the conductors, and, when the

conductors are strung to the tension limits recommended for vibration, the earth wire tension

limits stated above are usually not exceeded. If the limits are exceeded, satisfactory performance

can usually be obtained by the addition of a damping device to the earth wires. Because the

conductors generally have a higher thermal expansion coefficient than the earth wire, in cold

weather the clearance between the two will reduce if the line is not operational. This could lead

to flashovers when the line is energized. As an additional safety margin and also to improve the

shield angle at mid-span, earth wires should sag to 85 % of the sag of the conductors.

7.7 Anti-climbs

An anti-climb shall serve as a deterrent to unauthorized persons from climbing support

structures. All support structures for overhead lines or pole mounted transformers shall be fitted

with anti-climbs. These shall be of the nature of steel spikes, barbered wire or razor wire and

come at a height of significant safety. The recommended minimum height shall be not less than

3m above ground, but within standard height clearance from the overhead conductor.

7.8 Cradle Catch nets

At points of crossing overhead lines of system voltage of 11kV and 33kV at major commercial

roads, rail lines and other voltage power lines, a catch net shall be provided under the overhead

lines with the highest system voltage at not less than 1.2m without bleaching clearances of the

other voltages.

7.9 Red Balls

81

Where there is extreme aviation proximity with power overhead lines, visible red balls will be

placed on over the conductors in that vicinity as per guidance of relevant standards.

7.10 Goal posts

For 11kV and 33kV overhead lines heavy machinery crossings, goal posts will be erected at the

designated crossing point for that machinery under the overhead lines.

7.11 Pole Mounted Equipment

7.11.1. Switches

7.11.1.1. Line Isolation Switch

Isolators shall comply with the requirements of IEC 60129 and IEC 60265-1. The switch shall

be of the triple pole, gang operated, rocking type, spring assisted manually operated preferably

having hinged blades and front connections and shall be capable of breaking full load current at

a power factor 0.7 leading. The isolators shall be capable of making the system fault current

specified in the Technical Schedules, without damage to the equipment or danger to the

operator.

7.11.1.2. Isolator with Earth Switch

The equipment shall comprise a line isolator integral with an earth switch and shall be suitable

for pole mounted operation.

The line isolation switches shall be fitted with approved type three phase earthing switches to be

located on either the top or the bottom contact terminals of the switch.

The earth switch shall be of three pole construction, spring assisted manually operated and fully

rated for the system fault rating. The earth switch shall form an integral part of the main switch.

Two independent earthing pads with connectors suitable for the specified size of the earth

conductor shall be provided, one at each end of the switch.

The main switch and the earth switch shall be mechanically interlocked such that it will not be

possible to close the earth switch when the main switch is closed. The rated peak short circuit

current and the rated short time current of the earthing switch.

7.11.1.3. Switch Fuses

Switch fuses shall comply with the requirements of IEC 60129 and IEC 60265 and shall meet

the interrupting current requirements of IEC 282-2.

The design and mounting shall be such as to permit easy operation from ground level using an

operating rod i.e. an operating eye shall be provided on the fuse tube designed for use with a

hook stick.

The fuse holder of a switch fuse shall be dimensionally compatible with a universal fuse link of

corresponding rating.

The main assembly may be mounted on a two insulator base arrangement, the top and bottom

contact sub-assemblies and mounting fitting shall be fitted into the porcelain insulators, the

82

upper fixed contacts shall positively latch. Insulators shall be of the solid glazed porcelain type

and be bird proof, they shall meet the electrical and mechanical characteristics of IEC 383 and

provide a minimum creepage distance as specified in SP-GGE-001 and in the Technical

Schedules.

The assembly shall be designed such that the tube can be closed without using undue care even

when the closing force is applied at an angle. The angle of the fuse tube or link relative to the

vertical shall be a minimum of 20o.

The fuse tube shall be capable of accepting IEC/BS EN fuse links.

The toggle mechanism shall provide locking action to protect the fuse link from shock. A

spring assisted flipper shall assist arc interruption by withdrawal of the fuse tail.

The fuse tube cap shall preferably be of the non-expendable type and an arc shortening rod, if

provided, shall be attached to the fuse tube cap.

7.11.1.4. Isolator with Switch Fuse and Earth Switch

The equipment shall comprise a combined 33kV line isolator with switch fuse and earth switch

suitable for pole mounted outdoor operation. The fuse switch arrangement shall be mounted on

the same phase below the line isolator and shall comprise three single pole type expulsion fuses

or drop-out fuses as specified.

7.11.1.5. 11 and 33 kV Fuse Links

11 and 33 kV fuse links shall be general purpose, powder filled, fault limiting fuses and shall

comply with their requirements of IEC 60282 Part 1 and 2 and shall be suitable for use with fuse

isolators to be provided and shall be so rated and shall have such fusing characteristics as to be

suitable for selective operations with the fuse links presently in use on the system.

All current carrying parts of the fuse links shall be on non-ferrous materials, the main

requirements being resistance to atmospheric corrosion.

Each fuse link shall be permanently marked with the following information:-

Vendor or identifying mark, current rating, type designation (e.g. K or T).

The switch fuse mechanical arrangement shall allow for any rating or dimension of the fuse,

within the standard design of the isolator including modifications required, if any.

7.11.1.6. Drop Out Fuses and Line Links

These shall be single phase pole mounted link stick operated. They shall be provided on pole

mounted transformer supplies and on overhead line Tee-Offs at 11kV and 33kV.. The mounting

arrangement shall be as detailed in the attached detail drawing.

Fusible links shall be designed to carry 150% of their rated current without deterioration of the

fusible element or damage to the cut-out unit in which they are installed. Melting of the element

shall cause the cut-out link to be expelled from the line contacts.

All metallic hardware and components of fuses and links shall be hot-dip galvanised. .

83

7.11.1.7. Operating Mechanisms

The switches along with their interlocked earth switches shall be complete with gang/manually

operated switch opening and spring assisted push button triggered closing operating

mechanisms. The mechanism drive and linkage of the isolator shall allow the operating handle

to be mounted about 1.25 metres above the ground and shall be designed to minimize wear and

permit some degree of misalignment of the structure. It shall be as simple as possible

comprising a minimum of bearing and wearing parts. Shaft and pin bearings shall be of self-

lubricating or dry type and shall be such as to permit easy manual operation by one person even

following long periods of non-operation. The operating rod shall have an insulator insert of

wood (e.g. Permalli) or approved equivalent, the insulating medium used to be stated by the

Contractor.

The mechanism shall provide simultaneous isolation of all three phases and arranged for up-

‟ON‟ operation.

The closing mechanism shall be a spring assisted manual device designed so that the speed of

operation is independent of the operator. The mechanism shall be of robust construction and

shall be carefully fitted to ensure a quick, smooth simple and effective operation. The time of

operation shall be as fast as possible.

The operating mechanism shall be of substantial construction utilising such materials as may be

necessary to prevent sticking due to rust or corrosion. The ganged switching mechanism shall

be provided with sufficient adjustment to allow for final alignment of the switch blades for

simultaneous operation. Adjustable stops shall be provided to prevent over travel in either

direction.

It shall not be possible after final adjustment has been made, for any part of the mechanism to

be displaced at any point in the travel sufficiently to allow improper functioning of the switch

when the switch is opened or closed at any speed.

The overall design of the mechanism shall be such as to reduce mechanical shock to a minimum

and shall prevent its inadvertent operation due to fault current stresses, vibrations or other

causes. The mechanisms shall be self-locking in both the open and closed position and shall be

of a type that shall operate all three phases simultaneously.

The operating mechanism shall be suitable for manual off operation by means of the operating

handle positioned as specified above on the overhead line structure and push button triggered

“ON‟ operation after the spring is charged using the operating handle.

The operating mechanism and operating handle shall be complete with all supporting

accessories, all brackets, angles, guides or guide bearings or other members as may be required

for attaching the operating mechanism and operating handles to the wood pole structures. All

bearings as required shall be weather protected by means of covers. The lubrication

requirements shall be as specified.

The connecting assembly between the mechanism of the switches and their operating down rods

shall be robust and strong with a positive mechanical connection between linkages to provide

adequate gripping force in order to prevent slipping between the mechanisms during the

operating of the switches.

84

7.11.1.8. Accessories

7.11.1.8.1. Counter Balance Springs

These shall be provided as may be necessary for counter balancing the switches to prevent

impact at the end of travel both on opening and closing of the switch/earth switch. The springs

shall be of non-rusting alloy.

7.11.1.8.2. Earthing Pads

Each pole of the switch shall be provided with two earthing pads of non-corroding material at

opposite ends, brazed to the supporting base. Flexible copper earth connectors shall be provided

for connecting operating handles of switches/earth switches to the earthing system.

7.11.1.8.3. Position Indicator

A mechanical position indicating device shall be provided for each switch/earth switch.

7.11.1.8.4. Padlocks

The operating mechanism of each switch and the earth switch shall be provided with facilities

for locking the switch in the “OPEN” or “CLOSED” position. The facilities include those for

the spring charging handle and the closing push button.

7.11.1.8.5. Name Plate

A weather proof and corrosion proof name plate shall be provided on the switches, and the

operating devices. The name plates shall conform to IEC standards.

7.11.1.8.6. Live Line/Earthing Clamp Support

In order to carry out live line maintenance, clamp supports to receive a live line clamp and an

earthing clamp shall be provided adjacent to bottom terminal of line isolation switches and,

when equipped, at the bottom terminals of the fuses.

Necessary extension of the terminals shall be provided in order to enable proper support of the

clamps as described above. The extension shall be at least 150 mm long and shall have a 16

mm diameter hole to suit the dimension the cable lug to which connection shall be made.

7.11.2. Fencing off

All substations and pole mounted units shall be fenced off and locked out to avoid unauthorized

access to the structures.

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8. UNDERGROUND DISTRIBUTION SYSTEMS

8.1. Components

8.1.1. Cables

Cables shall be selected based on their suitability for the terrain and current carrying capacity

and shall be compliant to ZS 688.

8.1.1.1. Cable accessories such as glands, bolts and fasteners:

8.1.1.1.1. Cable Glands:

A gland is a cable terminating fastener used on armoured cable which may or may not include a

metallic inner sheath or screen, but shall be so constructed that provision is made to ensure

electrical earthing continuity between the armour of the cable and the metallic structure of the

enclosure to which the gland may be attached.

For further reference please make reference to SANS1213 and IEC 60079.

8.1.1.1.2. Bolts and nuts:

All metal parts shall be secured by means of bolts and nuts whose minimum diameter shall be

12mm. All bolts, nuts and screw threads shall comply with SABS 135 (there is no SANS

equivalent) and galvanized in accordance with SANS 121 unless otherwise approved. Bolts and

nuts shall be of steel with hexagonal heads. The nuts of all bolts for attaching to the tower plats,

brackets or angles supporting insulator sets or droppers to earth conductor clamps shall be

locked by approved means. No screwed threads shall form part of the shearing plane between

members. Unless otherwise approved, all bolts and screwed rods shall be galvanized including

the threaded portions; all nuts shall be galvanized with the exception of the threads, which shall

be greased. When in position all bolts or screwed rods shall project through corresponding nuts,

but such projection shall not exceed the diameter of the actual bolt.

Where different grades of steel are used, bolts of any given diameter and length shall conform to

the same grade of steel.

8.1.1.1.3. Junctions/Joints:

8.2. All joints shall comply with IEEE 404, IEC 60840 and SANS 10198-9 to 11.

Trenches:

Cables of voltages above 600V shall be buried at a minimum depth of 1000mm below ground

level and cables for voltages below and including 600volts shall be buried at a minimum depth

of 800mm..

Trenches shall not be less than 300mm wide for single and multiple LV service connection

cables, and the trench width shall be increased where more than two LV feeder or service

connection cables are laid together so that the cables may be placed at least 150mm apart

throughout the run. Cables installed in earth trenches shall be laid on a bedding of sand or soil

free of stones, and covered with the same material to a depth of at least 100 mm. Special

constructions of cables can be chosen, if necessary, to protect against chemical effects. Cable

routes shall be identified with cable route markers – SANS10142-2;

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Streetlight cables buried in trenches under un-tarred roads shall be buried in a trench with

minimum depth of 600mm and 300mm wide. Trenches under tarred roads shall be buried a

minimum of 500mm deep, and normally in HDPE corrugated sleeving of applicable size,

quantity and required spare quantities. Where the nature of the ground does not permit the

excavation of the cable trenches to the specified depth, the engineer may authorize trenches not

less than 500mm deep. Such authority shall be given in writing. The Contractor must take all the

necessary precautions to prevent trenching work being in any way a hazard to the public, and to

safeguard all structures, roads, railways, sewer works or other property from any risk of

subsidence and damage. Soil type shall be graded.

For further guidance on trenches make reference to IEC 60502, IEC60840, and BS6622.

8.3. Cable Trays/Racks

This is an assembly of cable supports consisting of cable tray lengths or cable rack lengths and

other system components such as cable tray/rack fittings, support devices, mounting/anchorage

devices and various accessories required to demarcate or segregate the cables, offer cable

retention on the tray/rack and covering devices.

For further guidance on installation, testing and use, please refer to IEC 61537: CABLE TRAY

SYSTEMS AND CABLE LADDER SYSTEMS FOR CABLE MANAGEMENT

8.4. Cable Route Markers

Cable route markers of approved manufacture shall be provided at each end of an underground

cable route and at all points where such routes deviate from a straight line. Joints in the cable

shall be marked and the maximum distance between route markers shall not exceed 100m.

For underground cabling, above ground route markers shall also be provided at every change of

direction in the routing and at both sides of road or pipeline crossings, except when cable

routing is already indicated by colored concrete pavement.

The cable markers shall be tapered blocks cast from concrete in accordance with approved detail

drawings

Each cable marker shall be buried with its upper face 100mm above the natural ground level.

Marking of cable markers shall also be in accordance with approved detail drawings.

For underground cable marking purposes non‐ corroding strips shall be used, each having

ample length to be wrapped twice around the cable and in which the cable number has been

imprinted by means of letter/cipher punches. For above ground cabling, plastic markers resistant

to the site conditions shall be strapped round the cables.

Tempering with the position of this installed cable markers shall be strictly prohibited and

supported with an inspection and maintenance regime in place for every installation.

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9. EARTHING AND LIGHTNING PROTECTION REQUIREMENTS

9.1. General

Every substation shall be provided with an earthing installation designed so that in both normal

and abnormal conditions there is no danger to persons in any place to which they have

legitimate access. The installation must be able to pass the maximum current from any fault

point back to the system neutral without establishing dangerous potential gradients in the

ground or dangerous potential drops between parts of the substation with which a person may be

in a simultaneous contact.

The design shall be such that the passage of fault current through the earthing system does not

result in any thermal or mechanical damage or damage to insulation of connected apparatus and

that protective gear, including surge protection is able to operate correctly. Measures shall be

taken to minimize high “substation potential rise” and “transferred potentials” as necessary.

Such measures are usually necessitated by large earth fault currents, particularly if these occur

in a substation in an area of higher than 250 ohm metres specific soil resistivity.

Substation earthing design shall be based on IEC Recommendations 634-5-54 and IEC 1219 -

93 The earthing installation shall be designed with earth electrodes as necessary to reduce step,

touch and mesh potentials within the substation to the permissible safe limits. Such potentials at

the substation boundaries and transferred potentials shall also be similarly reduced to safe levels

by approved means.

9.2. Earthing of Equipment

9.2.1. General

All earth conductors attached to structures shall be fixed by an approved means at

approximately 1 m centres. Bare copper conductors shall not be in direct contact with

galvanised surfaces except at approved electrical joints. Steps shall be taken to ensure

compliance with this requirement which shall be to the approval of the Engineer.

Each item of electrical apparatus shall be connected to the main earth conductor by means of a

separate subsidiary connection. Minor items of plant e.g. small fuse protected motors and field

mounted control equipment etc., may be connected to earth through their associated cable

armour provided that the armouring is connected at each end by copper tape and that the cable

gland is not relied upon for continuity. Any metalwork or chain link fencing around the

substation site shall be adequately earthed in an approved manner.

9.2.2. Earthing system

The earthing system will comprise a network of continuous main copper earthing conductor

installed in and around the substation buildings together with subsidiary and branch copper

conductors to the various items of electrical equipment in the substation. Where the earthing

system is installed outside the substations, it shall be to approval but shall be at a depth not less

than 500 mm.

The main earth conductor shall consist of copper wire or strip of minimum section 95 mm2.

Branch earth conductors shall be 70 mm2 Cu minimum section wire or strip.

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Cable sheaths may be earthed in groups by a separate branch connection to each item of

equipment in the group with the branch connections being connected by a single subsidiary

connection to the main earth conductor.

9.2.3. Earthing electrodes

Earth electrodes shall consist of round steel-cored copper rods not less than 16 mm diameter.

An earth electrode inspection pit shall be provided at each electrode (or set of electrodes) to

facilitate testing of individual items.

9.2.4. Terminations

The contact faces of earth terminals shall be cleaned before connections are made to the

earthing system.

Earth conductors shall be tinned before being clamped at each earth stud.

When earthing switchgear, connection points shall be positioned not less than 300 mm above

finished floor or ground level and preferably on a vertical plane. Foundation bolts shall not be

used for connections to the earthing system

9.2.5. Guards against mechanical damage

Where earthing conductors are exposed to mechanical damage galvanised sheet steel guards

shall be provided for protection.

9.2.6. Neutral Earthing Resistor

Earthing resistors shall be dry type installed into floor -mounting IP 31 classified hot dip

galvanised steel housing suitable for outdoor service. The resistors shall be complete with lifting

and jacking lugs, access panels, holding down bolts or clamps, high voltage, earth terminals,

connectors and connections as well as with bottom mounting U-bars for erection on the concrete

pad.

Provisions shall also be made for temporary bypassing the resistors with a maintenance earthing

device.. Each resistor shall be equipped with removable link at the earth side for checking the

resistance during bypass.

For connecting the resistors to the neutral, single core XLPE cables (specification see previous

clause) with outdoor terminations shall be used.

9.2.7. Earthing conductor

All grounding (earthing) and bonding conductors shall be insulated stranded copper conductors

unless otherwise specified. The insulation shall be green, green with a yellow stripe or properly

marked with a distinctive green coloring, green tape or stripe or green adhesive label.

9.2.8. Apparatus, Steel Structures and Overhead Shield wires

The frames of all electric apparatus and the bases of all structural steelwork shall be connected

by branches to the earth grid. All disconnector bases, earth terminals, and earthing switches,

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neutral current transformers, lightning arrester bases as well as tower and gantries on which

overhead shield wires are terminated shall be connected to earth grid.

Lightning arresters installed for the protection of transformers shall be connected by direct low

reactance paths both to the transformer tank and to the earth grid.

Capacitor voltage transformers used in connection with the line traps shall be connected by

direct low reactance paths to a single earth rod in addition to the earth grid.

Galvanised steel structures with sufficient area and current carrying capacity may be used as

part of the earth connection to post and strain insulators and to overhead shield wires which

shall be terminated directly on to the steelwork.

9.2.9. Operating Mechanisms and Control Kiosks

Disconnector and earthing switch operating mechanisms and circuit-breaker control kiosks not

integral with the circuit-breakers shall be connected to the earth system by a riser entirely

separate from that employed for earthing the apparatus structures. Such riser shall be connected

to equipotential earth mat which shall be provided beneath the position where an operator will

stand. This mat shall be joined to the earth grid.

9.2.10. Earthing of distribution transformers

The neutral terminals of the transformers shall be connected to earth grid with a bar isolated

from the transformer tank. This busbar shall be tied to the earthing grid via two separate risers.

The transformer tank shall be connected to the earth grid via two separate risers.

The following specifications shall be complimented by the following international and regional

standards, IEEE 80:2000, SANS 10200 and SANS 10292;

The transformer MV surge diverter earth shall be connected to the transformer tank

earthing stud.

The transformer tank earthing stud shall be connected to the MV three point star earth

electrode arrangement with insulated copper earth lead (size dependent on short circuit

rating -70mm2 minimum)

The transformer LV neutral shall be bonded to the transformer tank earthing stud (MV

earth) via a metal oxide valve (MOV) surge diverter to protect the transformer

The transformer LV phase surge diverter earths shall be connected to transformer neutral

bushing.

The transformer neutral bushing shall be connected to the LV three point star earth

electrode arrangement with 70mm2 insulated copper earth lead. This may be directly

from the transformer, or via the distribution kiosk/board earthing bar.

Bare portions of transformer MV and LV earth electrodes arrangements shall be

separated by at least 5000mm, so that the LV earth is outside the resistance area of the

MV earth.

The transformer MV earth electrodes arrangement and bare parts of consumer‟s ECC

shall be separated by at least 5000mm so that the ECC is outside the resistance area of

the MV earth.

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Where split earthing and combined earthing issues are raised, the following standards shall be

consulted and applied:

SANS 10200:Neutral Earthing in Medium Voltage Industrial Power Systems;

SANS 10292: Earthing of Low Voltage Distribution Systems.

9.2.11. 33/11/0.4 kV substations

The object of an earthing system in a substation is to provide under and around the substation a

surface which shall be at a uniform potential and near zero or absolute earth potential as

possible. The provision of such a surface of uniform potential under and around the substation

ensures that no human being in the substation is subject to shock or injury on the occurrence of

a short circuit or development of other abnormal conditions in the equipment installed in the

yard.

a). Mesh earthing

Mesh earthing comprises an earthing mat buried horizontally at a depth of about half-a meter

below the surface of ground and ground rods at suitable points. All non-current carrying parts

contribute little towards lowering the ground resistance. The earth mat is connected to following

in a substation:

i). The natural point of each system through its own independent earth.

ii). Equipment framework and other non-current carrying parts.

iii). The earth point of lightning arresters, capacitive voltage transformers, voltage

transformers, coupling capacitors and the lightning down conductors in the substation

through their permanent independent earth electrode.

iv). Substation fence.

b). Solidly grounded systems

Solid grounding refers to the connection of the neutral of the power transformer or grounding

transformer directly to the substation grounding or to the earth. The solidly-grounded system is

the most common system arrangement, and one of the most versatile. The most commonly-used

configuration is the solidly-grounded wye, because it will support single-phase, phase-to-

neutral loads.

Because of the reactance of the grounded transformer in series with the neutral circuit, a solid

connection does not provide a zero impedance neutral circuit. If the reactance of the system zero

sequence circuit is too great with respect to the positive sequence reactance, the objectives

sought in grounding, principally freedom from transient overvoltages, may not be achieved.

First, the system voltage with respect to ground is fixed by the phase-to-neutral winding voltage.

Because parts of the power system, such as equipment frames, are grounded, and the rest of the

environment essentially is at ground potential also, this has big implications for the system. It

means that the line-to-ground insulation level of equipment need only be as large as the phase-

to-neutral voltage, which is 57.7% of the phase-to-phase voltage.

It also means that the system is less susceptible to phase-to-ground voltage transients.

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Second, the system is suitable for supplying line-to-neutral loads. The operation of a single-

phase load connected between one phase and neutral will be the same on any phase since the

phase voltage magnitudes are equal. This system arrangement is very common, both at the

utilization level as 480 Y/277 V and 208 Y/120 V, and also on most utility distribution systems.

While the solidly-grounded wye system is by far the most common solidly-grounded system,

the wye arrangement is not the only arrangement that can be configured as a solidly grounded

system. The delta system can also be grounded this has a number of disadvantages. The phase-

to-ground voltages are not equal, and therefore the system is not suitable for single-phase loads.

And, without proper identification of the phases there is the risk of shock since one conductor.

A common characteristic of all solidly-grounded systems in general, is that a short-circuit to

ground will cause a large amount of short-circuit current to flow. This condition is known as a

ground fault and the voltage on the faulted phase is depressed and large current flows in the

faulted phase since the phase and fault impedance are small. The voltage and current on the

other two phases are not affected. The fact that a solidly-grounded system will support a large

ground fault current is an important characteristic of this type of system grounding and does

affect the system design.

c). Resistive grounding

One ground arrangement that has gained in popularity in recent years is the high-resistance

grounding arrangement. For low voltage systems, this arrangement typically consists of a wye

winding arrangement with the neutral connected to ground through a resistor. The resistor is

sized to allow 1-10 A to flow continuously if a ground fault occurs.

The resistor is sized to be less than or equal to the magnitude of the system charging capacitance

to ground. If the resistor is thus sized, the high-resistance grounded system is usually not

susceptible to the large transient overvoltages that an ungrounded system can experience. The

ground resistor is usually provided with taps to allow field adjustment of the resistance during

commissioning.

If no ground fault current is present, the phasor diagram for the system is the same as for a

solidly-grounded wye system However; if a ground fault occurs on one phase the system

response is that the ground fault current is limited by the grounding resistor. The faulted phase

voltage to ground in that case would be zero and the unfaulted phase voltages to ground would

be 173% of their values without a ground fault present. This is the same phenomenon exhibited

by the ungrounded system arrangement, except that the ground fault current is larger and

approximately in-phase with the phase-to-neutral voltage on the faulted phase. The limitation of

the ground fault current to such a low level, along with the absence of a solidly-grounded

system neutral, has the effect of making this system ground arrangement unsuitable for single-

phase line-to- neutral loads.

The ground fault current is not large enough to force its removal by taking the system off-line.

Therefore, the high-resistance grounded system has the same operational advantage in this

respect as the ungrounded system. However, in addition to the improved voltage transient

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response as discussed above, the high-resistance grounded system has the advantage of allowing

the location of a ground fault to be tracked.

d). Impedance grounding

In industrial and commercial facilities, reactance grounding is commonly used in the neutrals of

generators. In most generators, solid grounding may permit the level of ground-fault current

available from the generator to exceed the three-phase value for which its windings are braced.

For these cases, grounding of the generator neutral through an air-core reactance is the standard

solution for lowering the ground fault level. This reactance ideally limits the ground-fault

current to the three-phase available fault current and will allow the system to operate with

phase-to-neutral loads.

9.2.11.1. Ground Mounted Substations (33/0.4kV and 11/0.4kV)

A distribution transformer is normally connected in delta-star with the star winding supplying

the load. The neutral point of the star winding is then earthed either directly or through low

impedance. Where a distribution transformer is so connected that no neutral is available

(normally a transformer connected in star-delta with the delta winding supplying the load), an

artificial neutral point is created.

For a transformer which supplies only high voltage motors, neutral is frequently earthed via low

value impedance usually a resistor. This limits the earth fault currents and the voltage rise above

earth at the fault position. Intermediate switchboards and motor control centres are earthed via

the sheath/armoured wires of supply cables or via a separate earth continuity conductor or both.

It is good practice to provide an additional connection to structural steel work at each high

voltage motor by means of either a copper strip or an insulated lead.

9.2.11.2. Pole mounted substations (33/0.4kV and 11/0.4kV)

Where surge arresters are installed:

The main earth conductor between the surge arrester and the electrode system shall be

as short and straight as possible with no sharp bends.

Except at locations where it is necessary for an operator to carry out switching

operations, the electrode shall be installed at the base of the pole.

At locations where it is necessary for an operator to carry out switching operations the

earth electrode shall be installed 5m away from the pole to avoid unacceptable step

potentials close to the operator. Any earth conductor within 5m of the operating

position shall be insulated. The insulated conductor shall be installed inside a PVC duct

to provide additional mechanical protection and insulation. It also serves to maintain

the conductor in a slow bend which improves lightning performance.

The main earth conductor shall be insulated to a depth of 1m below ground level.

The earth electrode resistance value shall not exceed 10Ω.

Aerial Earth Guard Wire

Arc horns

Pole leaded Earth wire

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An earth down lead conductor (stranded galvanized steel wire, size ¾.00mm) shall be stapled to

each MV pole in a straight line from 500mm below the lowest conductive part at the top of the

pole to the bottom. The conductor shall not be wrapped around the pole at any point since this

will increase the reactance of the down lead. The interval between staples shall not exceed

500mm

9.2.12. Distribution lines

The permitted earth electrodes are given below.

Note: The use of rod electrodes is preferred but due to practical difficulties, particularly in urban

areas where damage can be caused to other services, cable electrodes are acceptable.

Function Network Fault level Electrode

Earth

Electrode

EPN Up to 4kA 35mm2 bare Hard drawn stranded copper

cable

SPN Up to 8kA 70mm2 bare Hard drawn stranded copper

cable

Rod Electrode EPN/SPN All 1m or 1.2m copper clad earth Rods

o The earth rods shall comply with the requirements of SANS 62305-3 with the additions

given below

o Earth rods shall comply with the requirements of SANS 1063, and earth electrodes shall be

installed in accordance with the requirements of SANS 10199.

o Specific attention is drawn to the requirements for explosive manufacturing and storage

areas (see 12.2).

Earth mat /and pit

Refer to IEEE 80 and ECS 06-0023

o A preformed earth mat (preferred and shown) or an earth mat constructed of bare

conductor shall be:

o Approximately 1m x 1m in size.

o Installed directly below where the operator will stand when operating the switchgear.

o Installed at a depth of 300mm below ground.

o Connected to the switch handle or control unit.

o Segregated from all other earthing conductors where possible.

o Protected above ground by a cable guard.

o Embedded below ground in earthing compound (two bags below and above) to protect

against theft (preformed mat only).

Lightning arrestors (line Arrestors) shall refer to IEC 60099 and ECS 06-0023

Pole mounted lightning spikes shall refer to standard IEC60099-4, SABS171

NOTE: Earthing for premises shall be covered under the Wiring standard

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9.2.13. Fence

Metallic fences shall be connected to earth grid at all supporting posts with 35sq.mm copper

conductor.

The gate shall be connected to an equipotential earth mat

9.2.14. Jointing and bonding

Joints shall have a resistance not exceeding that of an equivalent length of conductor and the

Engineer may require any joint to be tested to prove compliance with this requirement. All

underground connections shall be made by the thermoweld procedure or equivalent. No bolted

clamps shall be used for them.

No drilling of the earth conductor shall be allowed except for jointing or terminating

Joints and connections to the earthing system shall not reduce the current carrying capacity of

the earth conductor and shall be to approval.

Special precautions shall be taken to ensure that the available contact area is fully utilised in all

connections to plant and apparatus.

Connections to plant and equipment shall be carried out by using the earthing terminals

specified.

Stranded earthing conductors shall be terminated with sweated or crimped cable lugs.

9.3. Lightning protection

Protection against lightning shall be in accordance with IEC 62305

A substation has to be shielded against direct lightning strikes by provision of overhead earth

wires or spikes. This equipment is essential irrespective of the isokeraunic level of the area due

to serious consequences and damage to costly equipment in case substation is hit by a direct

stroke. The choice between these two methods depends upon several factors economy being the

most important consideration. Both the methods have been used sometimes even in the same

station.

Substations shall be provided with overhead earthed screens or spikes in accordance with the

requirements of IEC 62305 to protect against direct lightning stroke to the substation. Down

conductors shall be free of joints and they shall be protected by non-metallic sleeves for a height

of 1.5 m from the ground. Separate down conductors shall be used only when galvanised steel

structure has not sufficient area and current carrying capacity.

Generally an angle of shield of about 45° for the area between ground wires and, 30° for other

areas is considered adequate for the design of lightning protection system.

9.4. Insulation Co-ordination

Insulation Co-ordination shall be in accordance with IEC 60071-2

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10. VOLTAGE REGULATORS

10.1. General

Voltage regulation at the customer metering point shall not exceed:

• +10% for voltages less than 11kV. (Refer to ZS 387-1: 2011)

• +5% for voltages greater than or equal to 11kV

Designers of 11 and 33 kV networks shall ensure that under normal feeding arrangements the

11kV design voltage drop shall be less than 5%.

In cases of commercial and industrial customers the overall power factor for loads shall be 0.92

lagging or better, no leading power factor shall be permitted.

10.2. Secondary Transformer Voltage Regulation

10.2.1. Methods of Voltage regulation

10.2.1.1. Line Drop Compensation

Line drop compensation is applied in cases of poor regulation. To some Primary and Grid

Substations, use of this is dependent on the geographical location of the particular substation

and the nature of the circuits it feeds.

During the design of line drop compensations voltage control schemes, system volt drop

calculations for the feeders have to be conducted and the line drop compensation settings

applied accordingly. Distribution substations supplied from the Primary or Grid Substation shall

then have their taps set according to their distance (circuit length) from the source.

NOTE: The presence of embedded generation will affect the operation of Line Drop Compensation

rendering it inappropriate for some 11kV and 33kV networks.

10.2.1.2. Static Balancers

Interconnected Star Balancing Transformers, commonly known as Static Balancers improve

voltage regulation by redistributing some of the neutral current across the phases. They have

proved to be particularly useful on long LV feeders serving small numbers of customers by

improving the load balance.

10.2.1.3. Voltage Regulators

Where Line Drop Compensation is not appropriate, voltage regulators shall be used.

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11. CAPACITORS

11.1. Power Capacitors

The capacitor units or bank are the fundamental part in each power factor correction installation

and/or filter. A thorough study should therefore be performed in order to obtain optimal

capacitor design.

The capacitor current consists of fundamental and harmonic frequency components. As the

magnitude of harmonic components may be very high, especially in a tuned filter, it is necessary

to take them into account when defining rated values of the capacitors.

For filters the voltage increase on the capacitor caused by the series connection of the reactor

should be considered. Refer to IEC61642 (1997).

The capacitor bank is the fundamental part in each filter equipment. A thorough study should

therefore be performed in order to obtain optimum capacitor design.

The filter current consists of fundamental and harmonic frequency components. As the

magnitude of harmonic components may be very high, it is necessary to take them into account

when defining rated data of the capacitors.

The following definitions and designing criteria are specific to filter capacitors:

i). Rated capacitor voltage, rated capacitor current and tolerances: see the relevant capacitor

standard;

ii). The ratings of a capacitor should make allowances for element failure or fuse operation

and should co-ordinate with filter protection. During service, if the capacitance change

exceeds the acceptable range for the filter, the filter should be disconnected from the

system. For further reference, refer to IEC61642 (1997).

11.2. Shunt Capacitors

This type of power factor correction installation can be used when it is not necessary to take

measures to avoid resonance problems or to reduce harmonics. This is generally the case when

the resonant frequency given by the network inductance and the capacitance of the power factor

correction installation is relatively high and the harmonic content of the network (i.e. bus

voltage and harmonic currents generated by the loads) is very low.

It should however be understood that the total resulting capacitance of all power factor

correction installations connected to the low voltage side of one distribution transformer

determines the possibility of a harmonic resonance problem. Avoiding such problems when the

power factor correction installation is already in service can be more difficult and costly than at

the original installation time as it is often not possible to re-use existing capacitors, frames, etc.

11.3. Capacitor Banks

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11.3.1 General

This part of the specification covers the design, manufacture, delivery, transportation, and

commissioning of capacitor banks. The capacitors shall be installed indoors or outdoors as

specified along with the related inrush current reactors, switching facilities and protections.

All necessary equipment for the control, protection and supervision of the capacitor banks is

also deemed to be included.

The capacitor bank shall be factory mounted to a maximum possible extent to reduce the work

required at site.

The capacitor banks shall be designed as compactly as possible in order to reduce space

requirements.

The capacitor banks shall be designed for temperature class D (max. 55° C) for outdoor

installation and class B (max. 45° C) for indoor installation.

11.3.2 Capacitor Units

The capacitor banks shall comprise a series of single phase capacitor units suitably designed for

the required total amount of reactive power for the specified frequency and voltage.

The capacitor containers shall be of steel with an adequate corrosion protection. The final coat

shall comply with « light grey ».

The guaranteed minimum values of losses of the capacitor units shall include losses due to

discharge resistors which shall be mounted inside each unit to discharge each unit from peak

voltage to maximum 75 V in less than 10 minutes.

Internal fuses shall be provided in order to limit possible failure to a single capacitor element

only.

The capacitors shall be able to carry continuously 1.3 times the rated current 1.1 times the

maximum system voltage and shall provide continuously 1.35 times the rated output. All the

above requirements shall be fulfilled under maximum ambient temperature.

The dielectric material shall consist of an all film material being suitable to operate the

capacitors on continuous load under the specified ambient conditions. The impregnate shall be

of a hydrocarbon type fluid characterised by high electrical strength and adequate physical and

chemical properties and shall be non-PCB. Oil to conform to IEC 60296-03. Low toxicity is

required and the impregnate shall be a class III B combustible fluid as per IEC 60296-3.

Each capacitor shall have one or two bushings dependent on the mounting arrangement. For

outdoor installation a creepage distance of 50 mm/kV for open rack material or 25 mm/kV for

complete enclosed material and for indoor installation of 25 mm/kV shall be considered.

The arrangement of the fixing and the bushings shall be identical in order to easily exchange

and replace any capacitor element of the total capacitor bank. The terminals for bushings and

fixing elements shall be ISO standard (metric).

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11.3.3 Capacitor bank

A number of capacitor units shall be combined to capacitor banks in double star arrangement.

The modules shall be arranged as an assembly on suitably designed enclosure and

constructional members of aluminium to avoid any corrosion problem.

The capacitor banks shall include all necessary internal connections and busbars, insulators and

other fittings. The capacitor enclosure structure shall be designed to carry all required unit

capacitors and facilities, and the conductors comprising the incoming and outgoing circuits

under the loadings and factors of safety specified and to give the minimum phase and earth

clearances.

The safe removal and safe replacement of capacitor units shall minimise the dismantling of any

structural member, support, including insulators or main connections.

Where necessary, approved means shall be provided upon the capacitor equipment for the fixing

and bonding of external connections to secure efficient earthing. Steelwork and all items of the

capacitor equipment shall be bonded as necessary with copper straps of adequate cross-section.

In case of outdoor open rack installation tinned copper shall be used.

Approved facilities shall be provided to temporarily earth the connections and apparatus during

maintenance.

11.3.4 Switching Device

11.3.4.1 Source circuit breaker

The …KV Source circuit breaker is excluded from the scope of supply of the multi-stages

capacitor bank equipment. The contractor shall verify with the purchaser that the nominated

source circuit breaker is suitable for capacitor switching duties. Tenderers shall state in their

tender the circuit breaker requirements for the capacitor bank being offered

11.3.4.2 Capacitor switches

Each stage shall be controlled by a suitable SF6 circuit breaker for switching in and out the

respective capacitor stage, according to the capacitive demand required by the system operating

conditions

The tenderer shall provide details of the proposed circuit breaker in his tender, together with

evidence that they are suitable for switching duties and that the circuit breaker and associated

power equipment will not be subject to damaging over-voltages when switching.

11.3.5 Safety Interlocking and Earthing

Interlocking shall be provided to ensure that the access to the capacitor bank enclosure is not

possible until the associated main incoming circuit breaker has been racked and the faulty stage

has been locked out and circuit earth applied.

One earthing switch shall be provided in each capacitor stage and will be placed after the

automatic circuit breaker. For safety raison this earthing switch will be also interlocked with the

main outgoing feeder.

99

11.3.6 Reactor and discharge device

11.3.6.1 Current limiting reactor

The transient current that flows on energising shall not exceed the rated making current of the

circuit breaker controlling the capacitor bank stage. If necessary, current limiting reactor shall

be connected in series with each capacitor stage to limit the current to an acceptable value. The

current calculation which flows upon energising shall be declared and shall take into account the

contribution from parallel connected capacitor stages

Current limiting reactors shall be designed for the full system lightning impulse withstand level

The reactor shall be dry air cored, mounted on suitably rated support insulator.

11.3.6.2 Discharge devices

Discharge resistors, suitable to discharge the capacitors from peak rated voltage to less than 75

volt within 10 minutes shall be fitted within the capacitor container. Tenderer shall also propose

suitable fast-discharge devices for consideration that will achieve de-energization in less than 30

seconds

11.3.7 Capacitor Protection

The capacitor banks/units shall be provided completely with its internal and external protection

which is considered as part of the capacitor equipment.. Protection relays shall be of the

numerical type.

11.3.7.1 Fuses

Fuses shall be provided internally for protection of individual capacitor units. The fuses shall

not deteriorate when the capacitor is subjected to discharge testing nor the currents associated

with service operations of the capacitor equipment. Fuses shall only rupture in case the related

unit is subject to failure and shall be capable of breaking the current following a failure of the

capacitor unit without hazard from the fuse or the capacitor. The ruptured fuse of each element

shall withstand indefinitely the voltage imposed across it under all operating conditions.

The remaining capacitor units shall be able to operate within the capacitor bank without undue

disturbance for a present number of unit capacitor failures.

11.3.7.2 Unbalance Protection

Sensitive loss of capacitance and fuse failure detection and alarm facilities shall be provided.

The protection shall comprise two independently adjustable steps with separate alarm and

tripping contacts at each stage. The first stage is set to operate an alarm when a significant

number of capacitor units have failed and the second stage shall initiate tripping after a reset

time delay via a trip relay (block-close function) before the loss of capacitance has resulted in an

unacceptable over-loading of any capacitor. The Tenderer shall submit a table showing the

number of units that can be lost per phase and per series group for a period of 1 month without

derating of the capacitor bank and without reduction in the designed life of the capacitor. The

minimum number of unit capacitors to satisfy these requirements shall not be less than one.

The protection shall be insensitive against inrush and harmonic currents.

100

11.3.7.3 Overload and Over-current Protection

For each phase of each capacitor bank an overload and overcurrent protection system shall be

provided to protect the capacitors from excess current (rms), including harmonic currents.

11.3.7.3.1 Overload protection

A first alarm shall be given at a current of approx. 110 to 120 percent of the rated current if

applied for more than approx. 30 min. A second alarm (selectable by links for tripping as well)

shall be initiated at currents of 120 to 140 percent of the rated current suitably time delayed to

avoid spurious alarms (trippings) being situated during short time disturbances.

Each stage of the overload protection shall be independently adjustable.

11.3.7.3.2 Over-current protection

For currents above 140 percent of the rated current a time delayed relay shall be provided to

initiate tripping. An instantaneous element for initiating tripping at currents above 200 percent

of rated current, however properly secured against tripping due to inrush currents shall be added

per phase with separate alarm and trip contacts. Reference is made to the MV over-current

relays specified in Article of these specifications.

11.3.7.4 Over-voltage protection

Suitable over-voltage protection devices shall be provided to control transferred internal and

external over-voltages on the capacitor banks.

11.3.7.5 Loss of Capacitance

Facilities shall be provided to allow for safe, simple and quick identification of defective

capacitor units. Portable test equipment or other means shall be supplied being able to detect

defective units.

11.3.7.5.1 Protection Scheme

The protection scheme shall be designed to isolate the faulted capacitor stage without disruption

to the other stages. Schemes which require tripping the main incoming feeder circuit breaker are

not acceptable.

Over-voltage over-load and unbalance protections may be combined within proprietary relay

designed specifically for protection of capacitor banks.

11.3.8 Capacitor Bank Control

Automatic and manual switching control shall be provided for the different stages. Automatic

control shall be preferably provided by a numerical type of reactive power regulator including

harmonic current supervision and the operating mode of each capacitor bank shall be selectable

via an Auto/ Manual / Off switch. There shall be On / Off push buttons for manual Close/trip.

Manual closing shall only be possible with the selector switch in Manual position. Time delay

facilities shall be provided in the manual control circuit to inhibit any re-closing within a set

delay time. Delay time shall be adjustable over the range of 0-5 minutes.

The automatic control unit will initiate switching f the appropriate number of stages in or out of

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service. The control unit shall select the capacitor stage to be switched in and means shall be

provided to vary the duty cycle to ensure a reasonable distribution of switching operations

between different capacitor stages.

The control system shall provide facility for manual / remote switching out, both locally and

remotely from the control centre. Suitable indications of the status of the capacitor bank shall be

provided locally and made available for signalling to the control centre.

11.3.8.1 Control Panel

A modular panel housing the individual and master controllers is required to be supplied and

will be installed in the control room of the substation. The enclosures shall provide at least IP42

protection to the control equipment.

The capacitor bank will be controlled by a logic control scheme as specified in section below:

11.3.8.2 Controller

The controller shall automatically switch off the Capacitor Banks in the event of loss of the

system supply where applicable. The scheme must be capable of re-starting automatically

following restoration of supplies.

The automatic sequence of switching IN/OUT of the capacitor units in stages shall be controlled

by a programmable logic controller of the power factor controller (PFC).

The switching sequence shall be coordinated with the logic control of the sub-station device and

Voltage Control (VC) device, and these shall be selectable from manual selection facilities. The

switching steps shall be programmable to achieve switching of capacitor sub-banks through

stage controlled circuit breaker.

11.3.9 Power Factor Control

Where applicable, The PFC relay/equipment shall have a range suitable for proper selection of

switching In/Out of the Sub-banks to maintain the Target Power Factor via the PLC.

The relay PF setting range shall be:

The relay shall have as a minimum a digital display of PF, Target PF, Operation Time Delay,

voltage and current.

11.3.10 Testing

Each capacitor unit shall be routine tested to IEC 60871-1&2. Type test certification according

to IE C60871-1&2.

Type test evidence in lieu of tests shall only be accepted on units of identical construction and

similar rating to those proposed for this application.

Other equipment associated with that capacitor banks shall be subject to routine tests to the

relevant IEC standard.

102

12. FEEDER PILLAR

12.1. General

12.2. Specification for Feeder Pillars

12.2.1 General

12.2.1.1 Weatherproof Housing

The weatherproof housing shall be manufactured from sheet steel or other approved material

and designed for ground mounting on a flat base or pier at or slightly above ground level. Fixing

holes shall be provided complete with M16 foundation bolts. It shall be of a totally enclosed

design with cables entering from the bottom. The housing shall be arranged for front access only

by means of side hinged doors which shall be fitted with an internal document holder and a

locking bar to secure them top and bottom. The locking bar shall be operated by a central handle

which shall be lockable by means of a padlock.

The housing shall be dust and vermin proof but adequate ventilation shall be maintained to

permit natural circulation of filtered air.

Provision shall be made for the installation of an electrical heating device to prevent

condensation within the housing. Such heaters shall be of the metalclad convection type and

shall be continuously rated complete with fuses and control switch.

12.2.1.2 Incoming Cables, Links, Busbars and Conductors

Links, busbars and conductors shall be manufactured from hard drawn high conductivity copper

and arranged for access from the front only. The busbars must be fully shrouded.

Phase cables shall be connected to the distribution board busbars by pole operated hinged slow

break links. The neutral connection shall be made by means of a bolted copper link. Links shall

be of the same current rating as the associated busbar.

Busbar support insulators shall be capable of withstanding rated short circuit conditions without

undue stress and be resistant to mechanical shock and vibration however caused.

12.2.1.3 Distribution Circuits

Each distributor board shall be equipped for the number of 3 phase, 4 wire distributor circuits as

specified by the purchaser. Each phase circuit shall be controlled by high rupturing capacity

cartridge type fuse links which conform to IEC 60282 part 1&2;1994. Insulated dividing

barriers shall be provided between phase contact assemblies and phase and neutral contact

assemblies which shall make it impossible to insert a fuse link between contacts of different

phases.

12.2.1.4 Instrument Panel

The accessories to be provided on each distribution board are specified by the purchaser.

103

12.2.1.5 Future Requirement

The feeder circuits shall be so designed that additional current transformers can be easily

incorporated so that separate kilowatt hour meters can be installed to record the consumption in

each feeder.

12.2.1.6 Cable Glands

Each item of equipment shall be supplied with a complete set of screw type compression cable

glands suitable for outdoor use with those cables specified in the schedules. Each gland shall be

capable of carrying the short circuit current rating of its associated cable and be provided with

such fittings necessary for fixing in an untapped entry hole.

12.2.1.7 Cable Termination Lugs

Each item of equipment shall be supplied with a complete set of termination lugs and fixing

bolts for the types of cables specified by the purchaser.

12.2.1.8 Fuses and Fuse Carriers

12.2.1.8.1 Fuses for Distributor Circuits

The fuse links shall be in accordance with the requirements 0f IEC 60269 having single tag

contacts for insertion into spring loaded contacts. Each distribution pillar shall be provided with

an insulated fuse removal device.

The nominal rating of the fuses shall be one of the standard values within the range 125 A to

400 A. Within this range the fuses shall be of the same physical dimensions irrespective of the

rating.

12.2.1.8.2 Fuse links

All fuses shall be of appropriate duty, category and conform to IEC 60269. They shall be fully

interchangeable with those of any other make which conform to the dimensions described in

IEC 60269.

The fuse links shall be fitted with striker-pins to actuate the common trip-bar of the fuse switch.

12.2.1.8.3 Fuses for Auxiliary Supply

Fuse carriers for auxiliary circuits shall be of the withdrawable handle insulator type with a

rating of 60 A and shall accommodate cartridge type fuse links of 15 A, 30 A and 60 A ratings.

The fuse links shall conform to IEC 60269.

12.2.1.9 Enclosures

To conform to IEC 60529 (Degrees of Protection for Enclosures)

104

13. SUBSTATION CONCRETE WORKS

13.1 General

This section covers the construction of cast in-situ reinforced concrete slabs and plinths onto

which mechanical/electrical equipment is to be fixed, concrete slabs used for the protection of

cables as well as grouting and screeding.

13.2 Substation equipment plinths

13.2.1 Concreting

All concrete units will be solidly formed using concrete and steel reinforcing as indicated on

drawings which will be submitted to the engineer for approval within 30 days of the contract

having been awarded. Drawings will be submitted in threefold. Each unit will have rectangular

sides.

In general the edges of pockets for holding-down bolts or the centre-lines of holes drilled for

expansion bolts will not be closer than 100 mm to any concrete edge. The concrete unit will

furthermore be designed to be adequate to carry and distribute all live and imposed loads.

For concrete units to be constructed in situ, the excavation will be made 600 mm wider than the

outside dimensions of the unit and to a minimum depth of 200 mm below the lowest point of the

finished ground level (measured along the perimeter of the concrete unit). The bottom of the

excavation will be levelled and compacted to 93% of modified AASHTO density. A 50 mm

thick level concrete blinding layer will be cast covering the entire bottom of the excavation and

will be allowed to set for at least one day, after which the construction of the concrete unit

(fixing of reinforcement, erection of formwork, casting of concrete, etc) will take place. The top

of the concrete unit will protrude for a minimum of 200 mm above the highest point of the

finished ground level (measured along the perimeter of the unit). No concrete will be cast

without the engineer having had the opportunity to inspect and approve the formwork and

reinforcing. The formwork will not be removed before 7 days, and installation of

mechanical/electrical equipment will not commence until 28 days after the concrete have been

cast.

For concrete units constructed on floors which have been constructed by others, adequate

dowelling and bonding of the surfaces of the concrete unit and the existing floor will be

included.

13.2.1.1 Concrete mix

The following concrete mix will be used:

Cement (dry) 1 part per volume

Clean dry river sand 3 parts per volume

Crushed stone (10 mm) 6 parts per volume

The concrete will have 28-day minimum cube strength of 10 MPa.

13.2.2 Reinforcing

Standard brick force as used in 230 mm brick walls will be used as reinforcing and will be

indicated on the drawings.

105

All reinforcing will be inspected by the engineer prior to the concrete being cast.

13.2.3 Grouting

Grout under base plates and machine bases which are subjected only to gravity loading shall

consist of 1:1 sand, cement semi-dry mortar well caulked into the grouting space, unless

otherwise specified by the supplier of the equipment. The relevant concrete surfaces shall be

prepared by scrabbing and cleaning them. The mortar grout shall consist of an approved mixture

of cement, sand, water, and admixture, and shall be so rammed under each base or bedplate (as

applicable) that all voids and pockets are completely filled around the bolt or between the top of

the concrete and the underside of the metalwork, and, in the case of a base or a bedplate, that the

grout projects beyond the base or bedplate. After the void has been completely filled, the edges

of the mortar grout shall be trimmed at an angle of 45 outward from the bottom edges of each

base or bedplate and the trimmed edge wood-floated to a neat finish.

Grout used in bolted fastenings which are subjected to tensile, shear and/or vibration loads shall

be an approved epoxy mortar well caulked into the grouting space, bolt hole pocket or sleeve,

unless otherwise specified by the supplier of the equipment.

13.2.4 Dimensions

The dimensions shall be as indicated on the drawings provided.

13.2.5 Finishing

At all corners that are exposed after backfilling, the concrete will be chamfered 25 mm x 25

mm. The concrete will be well vibrated to eliminate cavities or honeycombing. Unformed

horizontal surfaces (top of concrete) will be floated with a wooden trowel to render a uniform,

skid resistant, horizontal surface.

13.2.6 Testing of Concrete

A sample from each batch of concrete will be taken by the Engineer or his representative for

testing purposes.

13.3 Oil containment tanks

(Definition - Refers to a vessel made from concrete or masonry that is usually wholly or

partially buried, that provides containment of lost oil and can also be an oil/water separator.)

13.3.1 Bund Walls

Bunds shall be designed to contain spillages and leaks of liquids used, stored or processed above

ground and to facilitate clean-up operations. As well as being used to prevent pollution of the

receiving environment, bunds are also used for fire protection, product recovery and process

isolation

106

14. WAYLEAVE

The requirements for the acquisition, management and operation of wayleaves shall be in

accordance with the Zambian Wayleave Code of Practice.

Notwithstanding the provisions of the Wayleave Code of Practice the following requirements

shall also apply:

14.1. General Requirements

General requirements relating to access to land and premises by a Distribution System Operator

are as follows:

14.1.1 Occupational staff and contractors acting for an electricity utility company will be

briefed on their responsibilities before entering private lands (or premises) or dealing

with owners.

14.1.2 The electricity utility company will take reasonable steps to contact the owner of the

land (or premises) before entering private lands (or premises). The company staff or

contractors will carry identification cards and produce this to the owner of the land (or

premises) when introducing themselves.

14.1.3 The owners of land (or premises) will be dealt with honestly and fairly.

14.1.4 Queries from the owner of the land (or premises) will be dealt with promptly and

courteously.

14.1.5 Company staff or contractors will only enter lands or premises for legitimate purposes

related to its licensed activities including surveying, maintenance, construction and

meter reading.

14.1.6 Company staff and contractors will take due care and attention to minimize land

damage by crews and equipment.

14.1.7 Due care and attention will be taken to minimize the risk of spreading any disease to or

from farmland.

14.1.8 Company staff and contractors will take reasonable steps to ensure that land (or

premises) is left in as good (or better) state than when Company staff or contractors

arrived.

14.1.9 Company staff and contractors will endeavor to ensure that restrictions on the use of

the land (or premises) during construction are minimized.

14.1.10 In the event of queries from the owner of the land (or premises) for further information,

a contact telephone number for the company will be advised to allow for such queries

to be dealt with.

14.2. Specific requirements

14.2.1 Staff shall take great care to close all gates behind them and not to damage

excessively fences or hedges. Any non-self-restoring damage done to fences or

hedges shall be made good by company staff within one month of agreement and any

damage which requires urgent attention shall be made good or rectified within one

week of notification.

107

14.2.2 Trial holes in advance of the main construction programmes, where necessary, shall

be opened only after consultation with the landowner. The method of carrying out this

work, shall be such as to cause the least disturbance. The trial holes shall either be

opened and filled in on the same day or made safe with fencing. The topsoil shall be

stacked to one side separately for reinstatement when refilling the hole. The subsoil

shall be properly compacted and the topsoil spread over it neatly. Rock and other

debris thrown up by the excavation shall be removed off the site by company staff.

Stones thrown up by the excavation shall be removed from the surface.

a). Before any construction work commences, a representative from the electricity

company will discuss the entry routes for construction and as far as possible give

the landowner the proposed programme of work and the date of commencement

of work.

b). Company representatives shall leave with the owner of land or premises, the

name and address of the person to be contacted in the event of any queries arising

out of the company‟s activities on the land or premises.

c). Where construction work is to take place and the entry routes have been agreed,

if the landowner requires, the agreed route shall be outlined by posts placed at

suitable intervals. These marking posts shall not be required in the case of single

entry, such as for wood

d). pole erection but must be provided, in the case of multiple entries such as

concreting operations.

14.2.3 The electricity company will cut up any trees that may be felled into transportable

lengths and bring them to the farmyard or other adjacent storage place. The company

shall dispose of rubbish and all debris from hedge and tree cutting caused by its

activities during line construction and maintenance operations. The landowner or his

representative shall be notified in advance of entry by the company for purposes of

hedge trimming and tree cutting in connection with line construction and

maintenance.

a). Fences shall be provided by the company as necessary for the protection of

persons, animals or crops and to prevent trespass. It must conform to the

reasonable requirements of the landowner. The type of fencing should depend on

its location, purpose and its expected stay in a particular location.

b). If a fenced off area crosses existing farm pathways or roadways, or other access

routes required by the landowner, the company shall provide a means of crossing

them to the reasonable requirements of the landowner, for passage of persons,

machinery and livestock.

c). All permanent pathways and roadways affected by the construction shall be

restored to their original condition before construction started or alternative

arrangements agreed.

d). Before construction work or trial boring operations commence, the landowner

shall notify the company insofar as he knows of the position, type and size of all

underground services, pipelines, drains and wells.

e). All watercourses and water supplies must be protected against pollution arising

108

from the work. All proper steps shall be taken to avoid any interference with

water supplies.

f). Where construction work interferes with drainage or septic tanks, these facilities

shall be maintained by the electricity company with the minimum of interruption

during the course of the work and the landowner shall provide all necessary

access facilities to enable the company to do so. They shall be subsequently

restored to the satisfaction of the landowner or an alternative equivalent service

provided.

g). All ditches, open drains or watercourses interfered with by the works shall be

maintained in effective condition during construction and finally restored to as

good a condition as before the commencement of works.

h). In excavation where rock has been removed from the foundations, priority shall

be given to the removal off site of broken rock where it is surplus to back filing

requirements, if required by the landowner.

i). On completion of works, the company shall remove all temporary buildings,

roadways, surplus soil, stone or gravel and any debris such as trees, brush woods

and any material that does not naturally belong on the site and was brought there

through the operations of the company.

j). The utility company, after consultation with the landowner, shall take all

necessary precautions to prevent the straying of livestock.

14.3. Prevention against Animal diseases

14.3.1 The utility company shall comply with any regulation which may be necessary in

connection with any Disease Eradication Scheme. The company shall ensure that the

local District Veterinary Officer is informed of the entry of company vehicles on farms

with a disease problem and that the Epidemiology Unit of the Department of Agriculture

is made aware of the company activities in a TB affected area.

14.3.2 Where possible the company shall not drive machinery through farmyards or other

places where there is an accumulation of animal manure. If this is necessary, the

company shall take adequate precautions to disinfect vehicles before and after entering

the land, especially on farms with a disease problem (or with neighbouring farms having

a disease problem), or where the company vehicles have recently been in a farm with a

disease problem.

109

15. LONG-TERM PRESERVATION OF SUPPORT STRUCTURES FOR

DISTRIBUTION INFRASTRUCTURE

15.1 Painting

The following paint and treatment shall apply to the listed types of poles;

Type of Poles Paint and treatment Exceptions (aviation

purposes)

Wooden Poles Creosote

(preservative)

Signal red and white

Concrete poles Gray Signal red and white

Steel poles Admiral gray Signal red and white

15.2 Concrete Poles

Concrete poles shall maintain the natural colour. Install reflective barrier for concrete poles in

close proximity to roads. Concrete shall be manufactured in line with SANS 470

15.3 Steel Poles

The Steel poles shall be hot dip galvanized in accordance to relevant Standards

Install reflective barrier for steel poles in close proximity to roads

15.4 Steel Structures for Outdoor Substations

Steel structures shall be hot dip galvanized in accordance to a relevant standards e.g. ZS

COMESA 293 AND IEC 61400.

110

APPENDICES

APPENDIX 1: INFORMATION REQUIRED WITH TRANSFORMER ENQUIRY

AND ORDER

A.1 Rating and general data

A.1.1 Normal information

The following information shall be given in all cases:

a). Particulars of the specifications to which the transformer shall comply;

b). Kind of transformer, for example, separate winding transformer, auto-transformer

or booster transformer;

c). Single or three-phase unit;

d). Number of phases in system;

e). Frequency;

f). Dry-type or oil-immersed type. If oil-immersed type, whether mineral oil or synthetic

insulating liquid. If dry-type, degree of protection (see IEC 60529).

g). Indoor or outdoor type.

h). Type of cooling.

i). Rated power for each winding and, for tapping range exceeding ± 5%, the

specified maximum current tapping, if applicable.

If the transformer is specified with alternative methods of cooling, the respective lower

power values are to be stated together with the rated power (which refers to the most

efficient cooling).

j). Rated voltage for each winding

k). For a transformer with tappings:

– which winding is tapped, the number of tappings, and the tapping range or tapping

step;

– whether 'off-circuit' or 'on-load' tap-changing is required;

– if the tapping range is more than ±5 %, the type of voltage variation, and the

location of the maximum current tapping, if applicable.

l). Highest voltage for equipment (Um) for each winding (with respect to insulation,

see IEC 60076-3).

m). Method of system earthing (for each winding).

n). Insulation level (see IEC 60076-3), for each winding.

o). Connection symbol and neutral terminals, if required for any winding.

p). Any peculiarities of installation, assembly, transport and handling. Restrictions on

dimensions and mass.

q). Details of auxiliary supply voltage (for fans and pumps, tap-changer, alarms, etc.).

r). Fittings required and an indication of the side from which meters, rating plates, oil-level

indicators, etc., shall be legible.

s). Type of oil preservation system.

t). For multi-winding transformers, required power-loading combinations, stating, when

necessary, the active and reactive outputs separately, especially in the case of multi-

winding auto-transformers.

A.1.2 Special information

The following additional information may need to be given:

a). If a lightning impulse voltage test is required, whether or not the test is to include

chopped waves (see IEC 60076-3).

b). Whether a stabilizing winding is required and, if so, the method of earthing.

c). Short-circuit impedance, or impedance range (see annex C). For multi-

winding transformers, any impedances that are specified for particular pairs of

windings (together with relevant reference ratings if percentage values are given).

d). Tolerances on voltage ratios and short-circuit impedances as left to agreement in table

1, or deviating from values given in the table.

e). Whether a generator transformer is to be connected to the generator directly or

through switchgear, and whether it will be subjected to load rejection conditions.

f). Whether a transformer is to be connected directly or by a short length of overhead line

to gas-insulated switchgear (GIS).

g). Altitude above sea-level, if in excess of 1 000 m (3 300 ft).

h). Special ambient temperature conditions or restrictions to circulation of cooling air.

i). Expected seismic activity at the installation site which requires special consideration.

j). Special installation space restrictions which may influence the insulation clearances

and terminal locations on the transformer.

k). Whether load current wave shape will be heavily distorted. Whether unbalanced three-

phase loading is anticipated. In both cases, details to be given.

l). Whether transformers will be subjected to frequent overcurrents, for example,

furnace transformers and traction feeding transformers.

m). Details of intended regular cyclic overloading other than covered by 4.2 (to enable the

rating of the transformer auxiliary equipment to be established).

n). Any other exceptional service conditions.

o). If a transformer has alternative winding connections, how they should be changed,

and which connection is required ex works.

p). Short-circuit characteristics of the connected systems (expressed as short-circuit

power or current, or system impedance data) and possible limitations affecting

the transformer design (see IEC 60076-5).

q). Whether sound-level measurement is to be carried out (see IEC 60551).

r). Vacuum withstand of the transformer tank and, possibly, the conservator, if a specific

value is required.

s). Any special tests not referred to above which may be required.

A.2 Parallel operation

If parallel operation with existing transformers is required, this shall be stated and the

following information on the existing transformers given:

a) Rated power.

b) Rated voltage ratio.

c) Voltage ratios corresponding to tappings other than the principal tapping.

d) Load loss at rated current on the principal tapping, corrected to the appropriate reference

temperature.

e) Short-circuit impedance on the principal tapping and at least on the extreme tappings, if

the tapping range of the tapped winding exceeds ±5 %.

f) Diagram of connections, or connection symbol, or both.

NOTE On multi-winding transformers, supplementary information will generally be

required.