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STUDY OF 440KV ISOLATORS A MINI PROJECT REPORT

Submitted to Jawaharlal Nehru Technological University, Hyderabad

in partial fulfillment of the requirement

for the award of the degree of

BACHELOR OF TECHNOLOGY

By

1.G.DURGA SANTOSH (09N75A0201)

2.R.SURESH KUMAR REDDY (08N71A0222)

3.SESHU.K.R (09N75A0203)

4.V.SANDEEP (08N71A0230)

Under the esteemed guidance of

Internal Guide External Guide

SAKTHI SREEDEVI.S M.MANOHAR

Department of Electrical and Electronics Engineering

D.R.K. INSTITUTE OF SCIENCE AND TECHNOLOGY

Bowrampet (v),Via Air Force Academy, Hyderabad-43.

2011-2012

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Department of Electrical and Electronics Engineering

D.R.K. INSTITUTE OF SCIENCE AND TECHNOLOGY

Bowrampet (v), via Air Force Academy, Hyderabad-43

CERTIFICATE

This is to certify that the mini project work entitled “STUDY OF 440KV ISOLATORS” submitted to Jawaharlal Nehru Technological University, Hyderabad in partial fullfillment of the requirements for the award of degree of BACHELOR OF TECHNOLOGY in the Dept. of ELECTRICAL AND ELECTRONICS ENGINEERING during the academic year 2011-12 is bonafied work by

1. G.DURGA SANTOSH (09N75A0201)

2. R.SURESH KUMAR REDDY (08N71A0222)

3. SESHU.K.R (09N75A0203)

4.V.SANDEEP (08N71A0230)

This work has been carried out under the guidance of

Sri. D. SRINIVASULU SAKTHI SREEDEVI.S

Associate Professor & HOD Assistant Professor

Dept. of Electrical&Electronics engg. Internal Guide,

D.R.K Inst. of Science and Tech. D.R.K Inst. of Science and Tech,

Bowrampet-500043. Bowrampet-500043.

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ACKNOWLEDGEMENTS

With great pleasure, we want to take this opportunity to express our heart-felt gratitude to all the people who helped in making this mini-project a grand success.

We are indebted to SIEMENS Ltd. (Hyderabad works) for giving us this opportunity to do this project. We express our deep sense of gratitude to Mr. M. Manohar (HR) and Mr.D. Satish (HR) for their constant support during the entire period of this mini-project.

We also like to thank Mr. G. Ravi Kumar (Manager – Manufacturing), Mr. G.Srinivas (Grad. Trainee –Manufaturing), for taking us through the production process of isolators.

We would like to express our happiness to Mr. Gopal Panigrahy (Manager – Quality), Mr. Ravi Chandra (Graduate Trainee – Quality) for their constant encouragement and support that they extended throughout our project.

We profoundly thank our HOD, of Electrical and Electronics Engineering, Mr.D.SRINIVASULU and Smt.SAKTHI SREEDEVI.S, Asst.Professor & Internal Guide, for their cooperation during our mini-project.

G.Durga Santosh – 09N75A0201

R.Suresh Kumar Reddy – 08N71A0222

Seshu.k.r – 09N75A0203

V.Sandeep – 08N71A0230

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ABSTRACT

Dis-connector or Isolator switch is used to make sure that an

electrical circuit can be completely de-energized for service or

maintenance, such switches are often found in electrical

distribution and industrial applications, where machinery must

have its source of driving power removed for adjustment or

repair. High-voltage isolation switches are used in electrical

substation to allow isolation of apparatus such as circuit

breaker, transformers and transmission lines for maintenance.

Isolators come in many shapes and sizes. Different types of

isolators are used based on the operating voltage of a power

system, current rating of the system, kind of sub-station, type of

operation used, amount of insulation required. Some of the

isolators are centre-break disconnectors, double-side break

disconnectors, knee type disconnectors, pantograph and semi-

pantograph disconnectors, vertical break disconnectors. The

isolators are tested for proper functioning of the device. In this

study project, a detailed and in-depth analysis of a 440KV (HV)

isolator is carried out. Their types, design, operation,

production, testing of isolator are considered.

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CONTENTS

1. INTRODUCTION.……..……………………..…..…..13

1.1. Scope ……………………………………..….…..….13

1.2. Definition.…………………………………….……...13

1.3. Functionality………………………………..……….13

1.4. Importance ...…………………………..……………14

1.5. Types of disconnectors…….………………………..14

2. TYPES AND RATINGS.…………………...…..…….16

2.1. Types………………………………………………....17

2.2. Ratings ...…………………………………………….18

3. DESIGN AND OPERATION ………….……..……..21

3.1. Introduction ………………………………………...21

3.2. Design Criteria …………………………….……….21

3.3. Design and Operation of Disconnectors ...…………26

3.3.1. Design & Operation of HCB Disconnector...……. .26

3.3.3. Design & Operation of Double Break Dis…………32

3.3.4. Design & Operation of Pantograph Dis…………... 39

3.4. Earth Switch ..……………………………………….39

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4. CONSTRUCTION AND ASSEMBLY …………..…40

4.1. Introduction …………………………………………40

4.2.Construction & Assembly of HCB Disconnector……..42

4.3. Construction and Assembly of DBR Disconnector....46

4.4. Construction and Assembly of PG Disconnector…….50

5. OPERATING MECHANISM AND TESTING….....53

5.1. Introduction………………………………………….53

5.2. Types of Operating Mechanism……………………...53

5.2.1. Manual Operating System without Gear …………..53

5.2.2. Manual Operating System with Gear ……………...54

5.2.3. Motor Operating System …………………………..54

5.3. Testing ……………………………………………….58

6. CONCLUSION..……………………………………...62

BIBLIOGRAPHY ..……………………………………...63

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LIST OF FIGURES

SNO FIG NO DESCRIPTION PG NO

1 1.1 H.C.B 14

2. 1.2 D.B.R 14

3. 1.3 P.G 14

4. 1.4 Substation Layout 15

5. 3.1 Aluminium contact 22

6. 3.2 Copper contact 22

7. 3.3 HCB DISCONNECTOR 26

8. 3.4 Parts of HCB 26

9. 3.5 Operation of HCB 28

10. 3.6 Skeleton view of HCB 28

11. 3.7 DBR Disconnector 29

12. 3.8 Operation of DBR 31

13. 3.9 Skeleton view of DBR 32

14. 3.10 PG Disconnector 33

15. 3.11 Parts of PG 34

16. 3.13 Gear Box of PG 35

17. 3.14 Operation of PG 37

18. 3.15 Structural diagram of PG 38

19. 3.16 Earth switch 39

20. 5.1 MOM box 55

21. 5.2 Circuit diagram of MOM box 56

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LIST OF TABLES

SNO TABLE DESCRIPTION PG NO

1. 2.1 Standard voltage ratings 19

2. 3.1 Voltage ratings 22

3. 3.2 HCB Operating limits 28

4. 3.3 Dimensions and ratings of HCB 29

5. 3.4 Dimensions and ratings of DBR 32

6. 3.5 Operating values of PG 38

Disconnector

7. 3.6 Dimensions and ratings 38 of PG disconnector

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1. INTRODUCTION

1.1 SCOPE:

This report applies to 440KV high voltage disconnectors

which operate at 50Hz frequency and used only for outdoor installation.

It also discusses the various types which can be implemented in the sub-

stations operation at this high voltage.

1.2 DEFINITION:

An Isolator or a Disconnector is a device employed in switchyard

to isolate the required section from the supply point. And it is also used

to divert this power flow from one section to another section. The names

‘isolator’ and ‘disconnector’ are used inter-changeably.

It is used to make sure that an electrical circuit can be

completely de-energized for service or maintenance. Such switches are

often found in electrical distribution and industrial applications, where

machinery must have its source of driving power removed for adjustment

or repair. High-voltage isolation switches are used in electrical

substations to allow isolation of apparatus such as circuit breakers,

transformers and transmission lines for maintenance.

1.3 FUNCTIONALITY:

• All Disconnectors are used to switch-in or switch-out only on no-load

conditions.

• A Disconnector is to carry rated current flowing through the system.

• It should also be capable of carrying the fault current in case of a

fault occurring in the power system, which may be for a short time like

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one second or three seconds as per the switchyard fault current

calculations.

1.4 IMPORTANCE:

In the modern period, the switchyards are going for unmanned

stations and with the advent of digital relays, the systems are totally

computerized. All the operations are being carried out away from the

switchyard through remote operation controls, SCADA systems etc.

1.5 TYPES OF DISCONNECTORS:

1) Horizontal centre break

Fig 1.1 horizontal centre break

2) Double Break disconnector

Fig 1.2 Double break disconnector

3) Pantograph Disconnector

Fig 1.3 Pantograph disconnector

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Fig 1.4 420KV Sub-station layout

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2. TYPES AND RATINGS

2.1 TYPES

2.1.1 Introduction:

The function of disconnectors in high voltage power systems, is

to provide electrical and visible isolation of one part of the system. The

isolation generally takes two forms:

1. Isolation related to normal day-to-day operation of the power system.

For example, shunt reactors required only during light load periods are

switched out using circuit breakers and then isolated by disconnectors

during peak load periods.

2. Isolation related to repair or maintenance on transmission lines or

station equipment such as transformers, circuit breakers and so on.

In the latter regard, the disconnectors are a major contributor to

personnel safety. In any power system safety practices require a so-

called guaranteed point of isolation with a visible break. And a

disconnector mechanically locked in the open position meets this

requirement.

If the disconnector is motor-operated, then the electrical circuit of

the operator is also visibly isolated by means of a knife switch or a

removable fuse link.

To serve the purpose of isolation, disconnectors are required

to have a greater voltage withstand capability across the open gap than

to ground. The purpose of this is to ensure that surge voltages originating

in the power system or due to lightning activity will more likely

cause flashover to ground than across the open gap. At system voltages of

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245 kV and below, this requirement adds at least 10% above the line to

ground voltage withstand capability. At system voltages of 300 kV and

above the requirement is stated as a bias voltage test, (i.e.) an AC

voltage applied to one side of the disconnector and a switching or

lightning surge applied to the other.

High voltage disconnectors come in a variety of types and

mounting arrangements. The most commonly found are given below

• Horizontal Centre Break Disconnector

• Double Break Disconnector

• Pantograph Disconnector

2.1.2 Horizontal Centre Break Disconnector:

The horizontal Centre Break Disconnector is also a simple

design of two post insulators which rotate and join the two

conducting parts. Centre Break disconnectors are used in outdoor high

voltage sub-stations. The disconnector is designed to operate under

severe cold conditions.

2.1.3 Double-Break Disconnector:

The Double Break Disconnector is a variation of the centre

break isolator. It has three columns of post insulators and the centre

post is movable and the remaining two are fixed. The movable

contact rotates and closes the fixed contacts. It is also used in

outdoor high voltage Sub-stations.

2.1.4 Pantograph Disconnector:

The Pantograph Disconnector is a divided support single

column disconnector with vertical isolating distance. It is used in

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outdoor high voltage Sub-stations. This type of disconnector permits

the design of modern switchgear installations with minimum-space

requirement.

2.2 RATINGS

The common ratings used for disconnectors, including their

operating devices and auxiliary equipment, are given below

• Rated Voltage (Ur)

• Rated Insulation level

• Rated frequency (fr)

• Rated normal current (Ir)

• Rated short-time withstand current(Ik)

• Rated peak withstand current (Ip)

• Rated duration of short circuit (tk)

• Rated supply voltage of closing and opening devices and of auxiliary

circuits (Ur)

• Rated supply frequency of closing and opening devices and of auxiliary

circuits

2.2.1 Rated voltage(Ur):

The rated voltage indicates the upper limit of the highest voltage

of systems for which the disconnector is intended. Standard values of rated

voltages are given below:

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Range 1(for rated voltages of ≤ 245kv)

Range 2(for rated voltage >

245kv)

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

300 KV – 362 KV – 420 KV – 550 KV –

800 KV

Table 2.1 Standard voltage ratings

2.2.2 Rated Insulation Level

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 over voltage patterns. The choice should be

made considering the degree of exposure to fast-front and slow-front

over-Voltages, the type of neutral earthing of the system and the type of

over-voltage limiting devices.

2.2.3 Rated frequency (fr)

The standard values of the rated frequency are 16.66 Hz, 25 Hz,

50 Hz and 60 Hz.

2.2.4 Rated normal current (Ir)

The rated normal current of disconnectors is the r.m.s. value

of the current which disconnectors shall be able to carry continuously

under specified conditions of use and behaviour.

2.2.5 Rated short-time withstand current (Ik)

The r.m.s. value of the current which the disconnector can carry in the closed position during a specified short time under prescribed conditions of use and behaviour.

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2.2.6 Rated peak withstand current(Ip)

The peak current associated with the first major loop of the

rated short-time withstand current which disconnectors can carry in

the closed position under prescribed conditions of use and behaviour.

2.2.7 Rated duration of short circuit (tk)

The interval of time for which a disconnector can carry, in the

closed position, a current equal to its rated short-time withstand current.

2.2.8 Rated supply voltage of closing and opening devices

and of auxiliary and control circuits (Ur):

The supply voltage of closing and opening devices and

auxiliary and control circuits is understood to mean the voltage

measured at the circuit terminals of the apparatus itself during its

operation, of opening and closing of the contacts.

The supply system is preferably referenced to earth (i.e. not

completely floating) in order to avoid the accumulation of dangerous

static voltages. The location of the earthing point is defined as a good

practice. It should be noted that normal operation of equipment is

assured when the supply voltage is within the tolerances.

2.2.9 Rated supply frequency of closing and opening devices

and of auxiliary circuits:

The standard values of rated supply frequency are DC, 50 Hz and

60 Hz.

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3.DESIGN AND OPERATION

3.1 Introduction

This chapter discusses about the design criteria and

constructional features of each and every type of disconnector.

3.2 Design Criteria

To design a disconnector, a lot of standards, specifications,

limitations, conditions are discussed and adopted in the best possible

way. The various types of disconnectors, which were discussed in the

previous chapter, have evolved because of these factors. Some of these

factors are discussed below.

3.2.1 Operating Conditions

• Ambient Temperature and Humidity

• Icing Conditions

• Wind Loads

• Seismic factor

• Altitude

• Induced electromagnetic disturbances

• Pollution factors (corrosive environment)

3.2.2 Application / Installation

The disconnectors can be installed in two ways

1. Outdoor Installation

2. Indoor Installation

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3.2.3 Current Path / Main Contacts Design:

The current path and the main contacts are designed using two metals.

They are

1. Copper

2. Aluminium

The metal used is dependent on many factors ranging from cost of the

disconnector to current rating and safety standards. The current path

design specifications are given by the user or customer.

Fig 3.1 Aluminium contact Fig 3.2 Copper contact

3.2.4 Types of mounting

Depending on the site layout, the mounting arrangement of the

disconnectors is classified utilize the available space in the switchyard or

substation to the best proximity. The different types of mounting are

• Upright (normal / staggered / series)

• Beam mounting / Gantry mounting / High-level mounting

• Vertical / Wall mounting

• Under Hung

• Pole mounting

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3.2.5 Voltage Rating

As per the high voltage switch gear products standards, and the

voltage ratings are categorized into two ranges

Range 1(for rated voltage ≤ 245kv) Range 2(for rated voltage > 245kv):

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

300 KV – 362 KV – 420 KV – 550 KV – 800 KV

Table 3.1 Voltage Ratings

3.2.6 Current Ratings

• Rated normal current(Ir)

The rated normal current of main contacts is the R.M.S. value of

the current which the disconnector shall be able to carry continuously

under specified conditions of use and behaviour.

• Temperature rise:

The temperature rise of any part of the disconnector at an ambient

air temperature shall not exceed the temperature-rise limits .

3.2.7 Short Time Current Rating

• Rated short time withstand current(Ik)

The R.M.S. value of the current which the disconnector can carry

in the closed position during a specified short time under prescribed

conditions of use and behaviour.

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• Rated Peak withstand current(Ip)

The peak current associated with the first major loop of the rated

short-time withstand current which disconnector can carry in the closed

position under prescribed conditions of use and behaviour.

• Rated Duration of short circuit(tk)

The interval of time for which the disconnector can carry a current

equals to its rated short time withstand current in the closed position. The

standard value of rated duration of short circuit is 1sec or 3secs.

3.2.8 Number of poles

The design of a disconnector is also dependent on the number of

poles used. The design may be implemented in the following ways.

• Single pole/one pole disconnector

• Double pole disconnector

• Triple pole disconnector

Though the 3-pole disconnector (required for 3-phase system)

design is standard in practice, in some cases like neutral earthing, single

pole/double pole disconnectors are also used.

3.2.9 Number of associated Earth switches

The disconnectors are equipped with earth switches to discharge

residual voltage, surge currents to the earth. Sometimes, due to many

factors like cost, space etc, earth switches are not at all used. Therefore,

the disconnectors could be

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• Without earth switch

• With one earth switch

• With two earth switches

3.2.10 Mode of Operation

The disconnectors/earthing switches can be operated with two

types of drive mechanisms depending on the requirements.

• Motor operated:

The motor coupled with a 2-stage reduction Worm-Spur gear to

increase the output torque. Motor can be a 3-phase 220/380/400/415/440

Volts AC, 50/60 Hz supply or DC 110/125/220 V supply depending on the

requirements.

• Manual operated

Handle operation: simply one lever is used to operate the equipment.

Crank handle operation with reduction gear mechanism.

3.2.11 Ganging Method

Ganging is said to be implemented when two or more

disconnectors are mounted side by side in a series of connected wall

boxes. It means that a group of disconnectors can be moved or controlled

by a single operating box. The disconnectors can be ganged in two ways:

• Mechanical Ganging

• Electrical Ganging

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3.3 Design and Operation of Disconnectors:

3.3.1 Design of HCB disconnector:

The horizontal Centre Break Disconnector is also a simple design of two

post insulators which rotate and join the two conducting parts. In this type

of disconnector, there are two moving contacts which are placed above

two separate rotating posts of sufficient insulation level and the contact

making/breaking will be done at the centre and hence the name

Horizontal Centre Break Disconnector. Horizontal Centre Break

disconnectors are majorly used in outdoor highvoltage sub-stations.

Fig 3.3 Horizontal Centre Break Disconnector

The various parts of a HCB are indicated in the diagram.

(1) Base Frame

(2) The operating mechanism

(3) Two rotatable seated supporting insulators

(4) The current path arms

(5) The rotating Unit. Fig.3.4 parts of HCB

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The support insulators are mounted on the mounting plate and

support both current path halves (finger and contact side) with the rotary

heads and high-tension terminals. This version offers freedom of

arrangement, since the high tension terminal can be turned within 360

degrees. Thus, the installation of a pipe connection or the straining of a

connection cable is possible from any direction.

The current path consists of a welded aluminium structure with a

minimum of terminal points and therefore no appreciable change of the

contact resistance over many years occurs. Disconnectors for a rated

voltage of 170 kV and above are equipped with an interlocking device,

consisting of a catch hook and an interlocking bolt which prevents the two

halves from separating in longitudinal direction in case of high short

circuit currents.

The optionally available earthing unit consists of a hinged type-

earthing switch fixed at the base frame. When in the open position, the

tubular arm is located along the base frame. In closed position the earthing

switch contact attached to the current path comes to rest between the

contact fingers of the earthing switch, which can be mounted either on the

contact side or the finger side or on both sides of the disconnector. The

universal design permits the earthing switch to be attached at site and it

can be retrofitted without any difficulty. All components are protected

against atmospheric influences; the steel parts liable to rusting being hot

galvanized.

3.3.1.2 Operating Principle

Disconnector and earthing switch are operated separately. The

design of the operating mechanism of the disconnector and earthing switch

is such that a dead centre position is passed through shortly before the end

positions are reached. Due to that, incidental opening or closing of the

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units due to external influences (e.g. short-circuits, storm, earthquake) is

impossible. The energy is transmitted from the operating mechanism of the

disconnector to a rotary pedestal.

The diagonal rods connect all rotary pedestals of each pole which

ensures simultaneous operation. The live part is very simple in its design

and motion as shown in fig 3.8. From the open position, the arms (1) and

(2) rotate together, synchronized by their linkage bar (3) to join in the

middle of the pole, and to close the main contact (4). (5) represents HV

terminals.

Fig 3.5 Operation Fig 3.6 Skeleton view of HCB

3.3.1.3 Technical Data and Dimensions

VOLTAGE

(KV)

CURRENT

(AMPS)

STC (KA RMS/1 or

3SECS)

MOVING BLADE

DESIGN

12 to 420KV 400 – 3150 A 12.5 - 40 Copper(12-245KV)

Al (12-420KV)

Table 3.2 HCB Operating limits

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Voltage (KV)

Current (amps)

Short time current(KA RMS 1/3 sec)

Dimensions A B C D

440 2000- 3150

40 4460 4100 3320 3650

Table.3.3 Dimensions and Ratings of HCB

3.3.2 Design of Double Break Disconnector (DBR)

The horizontal double-break disconnector consists of three poles.

Each pole consists of a frame, two supporting insulators at each end and

one rotating insulator in the centre, on which the main blade is mounted.

The contact making/breaking will be done at two ends simultaneously and

hence the name Double Break Disconnector.

Fig 3.7 Double Break Disconnector

3.3.2.1 Basic Constructional Features

The load-carrying constructional element of the disconnector is a

sectional-steel base frame. The middle one of the three insulators is fixed

on a common base frame and mounted on the rotary pedestal protected

against atmospheric influences and running on maintenance-free

assembled ball bearings. The middle insulator bears aluminium current

path.

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The main contacts of current path are made of silver-plated copper

profiles and the contact head is equipped with silver plated fingers. When

the disconnector is closing, the middle insulator rotates 70° until the main

contacts touch each other.

During final phase of closing the current path makes a rotation

round the longitudinal axis. This movement gives the best connection of

main contacts and makes it possible to break an ice coating.

The main contacts of the disconnector in closed and opened

position are locked via a dead centre system. The HV terminals are made

according to IEC standards. The current path consists of a welded

aluminium structure with a minimum of terminal points and therefore no

appreciable change of the contact resistance over many years occurs.

The optionally available earthing unit consists of a hinged type-

earthing switch fixed at the base frame. When in the open position, the

tubular arm is located along the base frame. In closed position the earthing

switch contact attached to the head of current path comes to rest between

the contact fingers of the earthing switch, which can be mounted on both

sides of the disconnector. The universal design permits the earthing switch

to be attached at site and it can be retrofitted without any difficulty.

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3.3.2.2 Operating Principle

The double break disconnector is

formed by three poles, operated

simultaneously either by a single operating

mechanism and mechanical linkages between

the poles or by one mechanism for each pole.

The base frame supports two

insulators and a rotating insulating rod (drive

insulator), which supports and operates the

arm.

The live part is very simple in its

design and motion. From the open position,

the arm (1) rotates to enter directly the fixed

contacts (2) at the ends of the disconnector. Fig 3.8 Operation of DBR

3.3.2.3 Technical data and specifications

The operating specifications of a double break disconnector are given

below.

VOLTAGE

(KV)

CURRENT

(AMPS)

STC (KA RMS/1 or 3SECS)

MOVING BLADE

DESIGN

12 to 420KV

400 – 3150 A

12.5 - 40

Copper(12-245KV)

Al (12-420KV)

Table No. 3.3 Operating Limits

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The dimensional or structural

view of a DBR disconnector is

shown in fig. 3.12. The different

dimensions of a DBR

disconnector for different voltage

ratings are given the table in the

next page.

Fig 3.9 skeleton view of DBR

Voltage (KV)

Current (amps)

Short time current(KA RMS 1/3 sec)

Dimensions

A

B

C

D

440 2000-3150 40 4510 4800 4000 3650

Table:3.4 Dimensions and rating of DBR

3.3.3 Design of Pantograph Disconnector

The Pantograph Disconnector is a divided support single column

disconnector with vertical isolating distance used in outdoor high voltage

Sub-stations. This type of disconnectors permits the design of modern

switchgear installations with minimum-space requirement.

In this type of disconnector, the fixed contact is connected to the

top bus and the moving contact is connected to the lower bus. With

pantograph principle the vertical reaching contacts of the moving contact

will make / break the circuit and hence the name Pantograph. Unlike other

disconnectors this will have different support arrangements for fixed

contact and moving contact separately.

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Fig 3.10 Pantograph Disconnector

The pantograph disconnector helps reach higher bus-bars and

transfers the electrical energy to another set of bus-bars which are at a

lower height. This is particularly helpful because wires cannot be hanged

to connect two bus-bars at different levels. So a pantograph being a rigid

structure which can withstand heavy winds, earthquakes etc. It has arms

which are placed in cross-hair shape. They stretch out to reach the bus-

bars.

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3.3.3.1 Basic Constructional features:

Fig 3.11 Parts of Pantograph Disconnector

The stable frame carries the constructional element of the disconnector. It

is mounted to the foundation by means of four studs (3) and supports the

support insulator (4) with intermediate piece (6), gear box (7), and the

pantograph (8), as well as the pivot bearing

(9) with the rotary insulator (5) and, if

available, the built-in earthing switch (10)

with its pivot bearing (12). The top

intermediate piece (6) is arranged between

the support insulator (4) and the gearbox (7)

with the pantograph (8). It serves as

mounting point for the bottom conductor. Fig 3.12 Turning Mechanism

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Adaptation of the top intermediate piece to the respective installation

needs (e.g. equipment with 2 or 4 cable pulleys for straining of the cable

bus bars), helps to reduce the number of structural elements and thus the

work involved in mounting. In the case of disconnectors witch built-on

earthing switches, the earthing switch contact is attached to the top

intermediate piece.

The pantograph has the welded

aluminium construction and together

with the cast aluminium gearbox

forms a mechanical unit.

The construction guarantees the

highest possible degree of mechanical

stability and reliable current transfer

especially in case of the short circuit.

Bolt connections are generally

avoided so that operating reliability is

not impaired with time due to the

bolts working loose or by corrosion in

the joint.

Fig 3.13 housing (gear box)

To balance the weight of the pantograph, the gearbox is mounted a

counterbalance spring. Because gearbox is closed on all sides the installed

components are protected against atmospheric influences, contamination

and animals (e.g. birds, snakes) as well as their nests. On all four sides are

provided flat terminals offering universal connection possibilities. The

entire transmission system has a simple mechanical design.

All gearbox and pantograph bearings are permanently lubricated

and thus maintenance-free. Disconnectors for high short-circuit currents

36

are equipped with a damper. This damper is mounted between the

pantographs joints and is to damp the vibrations caused by the short-circuit

current in the pantograph.

The suspended contact is situated above the disconnector on the

overhead line and is grasped with a high pressure, when the pantograph is

in closed position. Current is transferred through the pantograph joints by

tapered roller contacts and further through the gearbox. These connections

have been proven correct for many years operation under extreme

conditions in wet and cold climate, and their operating durability is

considerably higher than that of the still widely used multi-strand

conductors which are more susceptible to corrosion because of their large

surface area.

3.3.3.2 Operating Principle:

All disconnectors are supplied with manual operating mechanism

or motor-operated mechanism depending on the requirement and sub-

station layout. Each pole of the disconnectors and earthing switches is

actuated by a separate operating mechanism. The base plate supports the

insulator on which the upper frame is bolted. The rotating insulating rod

(driving insulator), which operates the moving contact is directly

connected to the operating mechanism. The torque from the motor of

operating mechanism is transmitted through the operating shaft and rotary

insulator to the top bearing in the gearbox and from there to both

pantograph arms by means of operating rods.

From the open position, the insulating rod (1) rotates to move the

arms through the geared system inside the upper frame (2). The lower

arms (3) raise together and close the jaws of the upper arms (4) on the

fixed contact bar (5). After having reached the final closed position, the

37

moving part is locked by a dead-point passing, preventing any accidental

opening. The flat HV terminals (6) are made according to IEC standards.

During making or breaking, before reaching its final position the

operating lever in the gearbox travels through a dead centre position, thus

preventing the pantograph arms of the

disconnector from opening and closing

incidentally.

The contact strips on the

pantograph arms during making

operation travel through a wide reach

angle and that guarantees reliable

grasping of the suspended contact even

if its position changes considerably

due to the influence of adverse

weather conditions (e.g. strong wind).

Fig 3.14 operation of pantograph

The high contact pressure in closed position does not only assure reliable

current transfer but also reduces contact wear. Due to the scissors’ action

when making and breaking the forces acting on the contacts of the

disconnector are concentrated on a single point so that even thick layers of

ice can be easily broken and removed

The design of the disconnector prevents formation of ice block

between the pantograph and gearbox. The corona protection fittings

attached to the pantograph arms also serve as a catching device in case of

vertical movement of the suspended contact and thus preventing the

suspended contact from slipping out of the pantograph arms.

38

3.3.3.3 Technical Data and Dimensions

The operating values of a pantograph disconnector are given below:

VOLTAGE

(KV)

CURRENT

(AMPS)

STC (KA RMS/1 or

3SECS)

MOVING LADE

DESIGN

123 to

420KV

1600 –

3150A

31.5 - 40 Al (12-420KV)

Table 3.5. Operating Values of Pantograph Disconnector

The basic structural drawing of a

pantograph disconnector is shown in fig.

3.15.

The dimensions of pantograph

disconnector for various voltage ratings

is shown in table 3.6 below.

Fig 3.15 Structural Diagram of PG

Rated

voltage

(kv)

Rated

current

(amps)

Short time

current (KA

RMS 1/3 sec)

Dimensions (mm)

A

B

C

D

E

440KV 2000-

3150

40 2760 4738 3650 3150 15600

Table 3.6 Dimensions and Rating of PG disconnector

39

3.4 Earth Switch:

The use of earthing switches ensures absolute de-energisation of

high-voltage components in a circuit or switchgear. The earth switches can

be built as stand-alone or can be attached on other disconnectors.

According to the requirements, built-on earthing switches can be arranged

laterally or in inboard arrangement with respect to the position of the main

current path of the disconnector as needed. Some earthing switches are

designed for switching induced inductive and capacitive currents.

Fig 3.16 Earth Switch

40

4. CONSTRUCTION AND ASSEMBLY

4.1 Introduction

Disconnector is a device used in the transmission and grid

substations for the purpose of disconnecting the power source either for

maintenance purpose or for bus transfer. Disconnector functions as

continuous current carrying device to the other connected equipments such

as Circuit Breaker, CT's, PT's etc from the main busbar in each of the bay

in a sub-station. These are used primarily for the isolating of equipment

and sectionalizing electric circuit or even portion of main feeders for

special purposes, such as testing and maintenance. Generally these devices

are not rated to make or break load.

4.1.1 Major Parts of Disconnectors

• Main-contacts/current path assembly

The disconnectors are provided with current carrying contacts

which are designed and tested for rated currents. The entire contact surface

is silver plated. The design of contacts is such that they are self-aligning

and self-cleaning during the operation.

The material can be either copper/aluminium. To maintain the

constant pressure, springs are used in the design. However these springs do

not carry current and do not loose their characteristics due to heating

effects.

• Base frame/base channel assembly

Each pole of the disconnector shall be provided with a complete

fabrication and galvanized steel base provided with holes and designed for

41

mounting on a supporting structure. The base frame also consists of the

rotating stool base guided by bearings/bushings to mount the insulators.

• Insulators

The insulator unit / stack is designed for sufficient insulation level

and according to the rating of the disconnector. They are installed over the

base frame to support the main contact assembly.

• Operating mechanisms (motor drive / manual drive)

The operating mechanism is used for close / open operation of the

disconnector / earth switch from the ground level. The equipment can be

provided with motor or manual operating mechanism boxes. The down

operating pipe, top operating mechanism (TOM), push pipes are the

mechanical linkages employed in the design to transfer the motion from

the drive mechanism to main contacts.

• Earth switch

The disconnector can also be provided with its associated earth

switch. The earth switch can be placed only on one side of the

disconnector terminals called as with one earth switch, both sides of the

disconnector terminals called as with two earth switches and for some

disconnectors the earth switch need not be provided based on its

application. Independent operating mechanism will be provided for the

operation of earth switch.

The earth switch alone without the association of disconnector is

also required in some cases as bus-earth switch / maintenance earthing

switch.

42

4.2 Construction and Assembly of Horizontal Centre

Break Disconnector

The constructional features of a horizontal centre break disconnector are

explained below.

• Hamper Assembly

• Support Insulator

• Disconnector Base

• Inter Stack Coupling Pipes

• Phase Coupling Pipes

• Support Structure

• Operating Mechanism

• Interlocks

4.2.1 Hamper assembly

The Hamper assembly consists of two moving arms called the

male and female arms, each mounted onto the top of the rotating support

insulators. The arms are made out of tubular or channel sections of

aluminium alloy depending on the current and voltage ratings of the

disconnectors. The male copper contact and female copper contact fingers

are silver plated and mounted onto the arms.

The male and female hamper assemblies are connected to the

terminal stem by using multiple, flexible copper strips for the safe transfer

of current from the moving arm to the fixed terminal stem of the

43

disconnector. The copper flexible is bolted firmly at one end to the rotating

arm and at the other end of the terminal stem.

The contact between the male and female contact is a line contact

and the contacts provided are of the reverse loop type. Each contact finger

is provided with a contact spring which, ensures that the required pressure

of approximately nine kgs. per pair of fingers is maintained.

The terminal stem onto which the terminal connector is fixed is

made of aluminium alloy for 420kV, 2500A disconnectors & 245kV,

2500A disconnectors; and of copper for all 245kV and below

Disconnectors up to 2000A. For 3150A rated disconnectors, only copper

terminal stems are used, and wherever the copper terminals are provided

the terminals are tin plated for connection to aluminium alloy terminal

connectors. Contact corona rings are provided at the male and female

hampers wherever necessary.

4.2.2 Support Insulators

The support insulators in the case of the centre break

disconnectors are used to support metallic hampers of the disconnectors

and to rotate through 90 degrees to open and close the disconnectors, to

provide necessary insulation between live parts and ground. Insulator

corona rings are provided on the insulators wherever necessary.

4.2.3 Disconnector Base

Disconnector base is made out of welded assembly. The base

consists of two flanges at either ends for mounting the support insulators.

These flanges are provided with the necessary holes at the required pitch

circle diameter to match the holes provided on the base flange of the

insulator.

44

The flanges are welded on the bearing shaft and are assembled

with two numbers taper roller bearings, Ball bearings with Al casting.

These taper roller bearings are seated one on the top and one on the bottom

of the base assembly and these ensure free and smooth movement of

disconnector arms. Bearing covers are provided to ensure that water and

dust do not enter the bearings. Provision is made at the two ends of the

bases to mount earth switches if required. Provision is also made on the

base for mounting the mechanical constructional interlock between

disconnector and earth switch wherever required.

The base is provided with mounting arrangement at two points for

fixing the disconnector base with the supporting structure. Earthing pad /

earthing studs are provided at two points at the extreme ends of the base

for connecting to the sub-station earthing system.

4.2.4 Inter Stack Coupling Pipes

Inter stack coupling pipes are provided to couple the two columns

on the same phase of disconnector so as to ensure simultaneous rotation of

the two poles columns driven by the common operating mechanism. The

coupling pipes are linked to the base flange on which the insulator is

mounted by metallic pin to ensure easy assembly / dismantling at site.

Normally the inter pole coupling pipes are assembled on to the base and

set at factory prior to dispatch from works.

4.2.5 Phase Coupling Pipes

Inter Phase coupling pipes are provided to couple the three phases

of the Disconnector and operate all the three phases from a common

operating mechanism in the case of Mechanically Ganged three pole

Disconnectors. These are not required in the case of single pole

Disconnectors where each pole is operated by its own operating

45

mechanism. The coupling pipes are linked to one base flange on each

phase of the three pole disconnector. These are dispatched loose and are to

be assembled at site. Provision is available to do minor adjustments in

length of the coupling pipe to suit site conditions.

4.2.6 Support Structure

Wherever specified, support structure of tubular types for 400kV

disconnector with necessary foundation bolts can be supplied. Plates are

welded on to this tubular support structure fabricated out of welded sheet

steel for 400kV Disconnectors for mounting the operating mechanism

boxes, the operating mechanisms of the disconnectors / earth switches are

mounted on to the structure on plates provided, being bolted with the

angles that are provided on the mechanism box. The height of this support

structure can be varied to accommodate the bus height as required by the

sub-station layout and system.

4.2.7 Operating mechanism

Motor Operating mechanism or manual Operating Mechanisms

are used.

4.2.8 Interlocks

A Mechanical constructional interlock between the disconnector

and earth switch is used to ensure that the Earth Switch can be closed only

when the Disconnector is in the open position and vive versa. An electro-

mechanical bolt coil type interlock is used in each motor operating

mechanism for interlocking between manual and motor operation of

Disconnector / Earth switch. This ensures that the motor circuit is cut off

when the manual operation is under progress. In some cases, only

electrical bolt coils are provided as interlocks solely controlled by

electrical circuits.

46

4.3 Construction and Assembly of Double Break

Disconnector

• Rotating Hamper Assembly

• Fixed Contact Assemblies

• Support Insulators

• Disconnector Base

• Inter Phase Coupling Pipes

• Support Structure

• Operating Mechanism

• Interlocks

4.3.1 Rotating Hamper Assembly

The rotating hamper assembly consists of a tubular section of

aluminium alloy of adequate cross-section clamped at the centre point. It

rotates through 110 º for the closing /opening operation of the

disconnector. The size of the aluminium alloy tube and its thickness is

selected based on the continuous and short time current carrying capacity

of the required disconnector. Silver plated copper contacts are fixed on to

this rotating aluminium alloy blade at either ends.

Double Break Disconnectors are of a special design, having a turn

and twist feature. In this design, the disconnector blade first moves in the

horizontal plane until it touches a stopper on the fixed contact, then the

tubular blade itself rotates giving a twisting motion. Only during this

twisting movement, the contacts mounted on the moving blade actually

make contact with the fingers on the fixed contact assembly. This rotating

47

motion of the blades ensures that adequate contact pressure is built up

between the fixed and moving contacts for carrying the rated currents.

This design also has a further advantage that during the closing

operation of the disconnector, the actual current carrying surfaces do not

come into the contact till the twisting motion occurs, thereby ensuring that

there will not be any damage to the surfaces of the contacts during the

closing of disconnector. The contacts are of the self wiping nature and

clean the contact surfaces while closing and opening of Disconnector.

This type of contact arrangement is called the pressure relieving reverse

loop type.

The moving aluminium alloy blades are clamped onto the turn and

twist mechanism which is housed in an aluminium housing for 420kV and

245kV Disconnectors. The turn and twist mechanism flange is then

mounted on to top flange of the centre insulator of each pole.

4.3.2 Fixed Contact Assemblies

Each pole of the Disconnector consists of two fixed contact

assemblies. The fixed contact assembly consists of a housing onto which

the silver plated copper contact fingers are mounted. Each contact finger is

provided with a compression spring to ensure that the required contact

pressure is maintained. The fixed contact assembly also consists of a

terminal pad. The terminal connector is fixed onto this terminal pad on

four holes provided thereon.

4.3.3 Support Insulators

The Double Break Disconnector consists of three stacks of support

insulators per pole or 9 stacks per 3 pole disconnector. Out of the three

insulators per pole, the outer two insulators are stationary and centre

insulator rotates through 110 degrees for closing / opening of the

48

Disconnector. Due to this reason, this type of Disconnector is also referred

to as the Double Break Centre post Rotating type disconnector.

The fixed contact assemblies are mounted on top of the outer

stacks of insulator which are stationary and the turn and twist mechanism

along with the rotating hamper assembly is mounted on the centre stack of

insulator.

The function of the outer stack of insulator is to keep the fixed

contacts rigid, provide the necessary creepage distance and the insulation

between the live parts and ground. The function of the center stack of the

insulator is to rotate though 110° and provide the necessary creepage

distance and also the insulation between line parts and ground.

4.3.4 Disconnector Base

Disconnector base is made of welded assembly. The base consists

of three flanges, two at either ends or one at the centre for mounting the

support insulators. These flanges are provided with the necessary holes at

the required pitch circle diameter to match with the holes provided on the

insulator base flange. The two end flanges are welded on to the base of the

disconnector adaptors. The center flange is welded to the bearing shaft.

The bearing shaft is assembled with two numbers taper roller bearings,

aluminium bearing housing. These bearings are seated one on top and

another on bottom of the base assembly and these ensure smooth and free

movement of the Centre rotating post of the disconnectors. Bearing caps

are provided to ensure that water and dust do not enter the bearings.

Provision is made on the base for mounting the mechanical constructional

interlock between disconnector and earth switch wherever required. The

base is provided with mounting arrangements at four / eight points for

fixing the disconnector base the supporting structure. Earthing pad /

49

earthing studs are provided at two points at the extreme ends of the base

for connecting to the sub-station earthing systems.

4.3.5 Inter Phase Coupling Pipes

Inter Phase coupling pipes are provided to couple the three phases

of the Disconnector and operate all the three phases from a common

operating mechanism in the case of Mechanically-Ganged three pole

Disconnectors. These are not required in the case of single pole

Disconnectors where each pole is operated by its own operating

mechanism. The coupling pipes are linked to one base flange on each

phase of the three pole disconnector.

4.3.6 Support Structure

Wherever required, support structure of tubular types for 400kV

disconnector with necessary foundation are used. Plates are welded on to

this tubular support structure fabricated out of welded sheet steel for

400kV Disconnectors for mounting the operating mechanism boxes, the

operating mechanisms of the disconnectors / earth switches are mounted

on to the structure on plates provided, being bolted with the angles, that

are provided on the mechanism box. The height of this support structure

can be varied to accommodate the bus height as required by the sub-station

layout and system.

4.3.7 Operating Mechanism

Motor Operating mechanism or manual Operating Mechanisms are used.

4.3.8 Interlocks

A mechanical constructional interlock between the disconnector

and earth switch has been provided to ensure that the Earth Switch can be

closed only when the Disconnector is in the open position and vive versa.

50

An electro-mechanical castle key type interlock is used in each

motor operating mechanism for interlocking between manual and motor

operation of Disconnector / Earth switch. This ensures that the motor

circuit is cut off when the manual operation is under progress. In some

cases, only electrical bolt coils are provided as interlocks solely controlled

by electrical circuits.

4.4 Construction and Assembly of Pantograph Disconnector

• Trapeze contact

• Scissor Assembly

• Main Frame Assembly

• Support Insulator

• Operating Rod Insulator

• Support Structure

• Operating Mechanism

• Interlocks

4.4.1 Trapeze Contact

The trapeze contact consists of a silver plated copper tube

suspended by adjustable dropper rods, quadruple or twin spacers, which

are connected to upper quadruple or twin ACSR conductor bus. The

complete assembly of sets of spacers, two Aluminium dropper rods and

one silver plated copper tube totally form the Trapeze contact of

Pantograph Disconnector.

51

4.4.2 Scissor Assembly

The scissor assembly contains the four point contacts of silver

plated copper which makes contact with the suspended copper tube of this

trapeze assembly. The copper contacts are mounted on the Aluminium

alloy extrusions assembled in the form of a scissor. Current transfer

contacts are provided at the joints to ensure smooth transfer of current

from one moving part to the adjacent part. The scissor arms on one side

have counter balance springs to ensure smooth operations. Current transfer

contact consists of a male copper contact on one side and female contact

finger assembly on the opposite side. Corona rings are provided on the

scissor assembly at the upper contact point and also at the joints in the

scissor assembly.

4.4.3 Main Frame Assembly

Main Frame assembly consists of the main frame of the

Pantograph Disconnector on which the pantograph scissor are mounted.

This assembly also has the terminal pad at either end for connecting the

terminal connectors. The terminal pad is a plate of aluminium alloy with

four holes drilled on it for fixing the terminal connector. The main frame

assembly also has the base plate for mounting it on top of the solid core

support insulator. It also houses the bell Crank and levers connected to the

down operating rod insulator for the operation of the Disconnector.

4.4.4 Support Insulator

The support insulator is a soil core insulator which is primarily

used to support the metallic pole of the Pantograph Disconnector and also

to provide the required insulation between the live parts and ground. An

insulator corona ring is provided on top of the insulator. The lower portion

of the support Insulator is mounted on to the support structure column.

52

4.4.5 Operating Rod Insulator

While the support insulator explained earlier gives the necessary

rigid support for the metallic part (main frame assembly and scissors), the

operating rod insulator is used primarily for operating the pantograph

scissors and for providing insulation for the person operating the

Pantograph. The upper end of the insulator is connected to a bell crank for

operating the disconnector and the lower end is connected to the operating

mechanism through a down operating pipe.

4.4.6 Support Structure

Wherever required, support structure of tubular types with

necessary foundation bolts can be used. Plates are welded on to this

tubular support structure fabricated out of welded sheet steel for mounting

the operating mechanism boxes. Operating mechanism is mounted on to

the structure on three plates being bolted with three angles provided on the

mechanism box.The height of this support structure can be varied to

accommodate the height of Upper and Lower bus heights as required by

the sub-station layout and system.

4.4.7 Operating mechanism

Motor Operating mechanism or manual Operating Mechanisms

are used.

4.4.8 Interlocks

A Mechanical constructional interlock between the Main and

earth switch is used. An electro-mechanical castle key type interlock

between Disconnector and earth switch where earth switch is specified.

Electro mechanical castle Key Interlock is used in between electrical and

manual operation in motor operating mechanism.

53

5. OPERATING MECHANISM AND TESTING

5.1 Introduction

We have seen in earlier chapters that a disconnector is used to

open a circuit and disconnect a sub-station from main power supply. It is

achieved by using a proper operating mechanism to help it move from

close to open or vice-versa. The operating mechanism is installed in a box

of the main disconnector main blade which is connected by means of a

operating down pipe.

Without a properly functioning operating mechanism, a

disconnector cannot disconnect a circuit and it would be a drastic failure

and it will be deemed a big failure. So, the operating mechanism is the

heart of a disconnector. The disconnectors functionality depends on the

operating mechanism.

5.2 Types of operating mechanisms

The Disconnectors and Earthing switches are operated with the following

Operating Mechanisms:

• Manual operating mechanism

• Manual with gear mechanism

• Motor operating mechanism

5.2.1 Manual Operating Mechanism

The manual operating mechanism is provided with a handle to

operate the disconnector / earthing switch. Locking is done in both the

close and open conditions, i.e. to open a disconnector, a person has to go

to the operating mechanism box to manually open the disconnector.

54

Interlocking is done mechanically and auxiliary switches are used

for position indication and interlocking indication. This system is used for

lower voltage systems and is never used for a system of voltage rating

higher than 33KV.

5.2.2 Manual with gear operating mechanism

The manual with gear operating mechanism is provided with

worm and worm gear to achieve smooth operation and self locking of the

mechanism. This gear mechanism helps the operator so that a lesser

physical force is required to move the disconnector. Mechanical

interlocking mechanism is used. Auxiliary contacts for position indication

and interlocking with other equipments are housed in the operating

mechanism.

5.2.3 Motor Operated Mechanism (MOM)

This operating employs a motor to rotate or turn or move a

disconnector. The motor is placed inside the operating mechanism box.

Generally, a motor rotates at 1100 rpm. But a disconnector is

moved at 2 rpm. So in order to step down the rpm, we use a reduction gear

system. Therefore, the motor operating mechanism is provided with

double stage reduction gear system i.e. spur gears at first stage and worm

gear at second stage to achieve smooth operation and self locking of the

mechanism.

The gear can be operated by three phase AC Induction motors or

Permanent Magnet DC motors, though an induction motor is widely used.

Suitable thermal overload relays are provided to protect the motor from

overload.

55

Auxiliary contacts for position indication and interlocking with

other equipments are housed in the operating mechanism. If required make

before break (MBB) contacts can also be fitted with the auxiliary contact.

MBB is a type of contact arrangement of an electrical switch, which

ensures that when a switch transition happens, the new contact is always

made before the old one is broken.

FIG 5.1 MOTOR OPERATING MECHANISM(MOM) BOX

The figure 5.1 shows a typical MOM box. The various parts of MOM is

given below:

1. AC (Induction) motor or DC motor (permanent magnet)

2. Reduction Gear box

3. Auxiliary switch

4. Contactors

56

5. Terminals

6. Start and Stop buttons

7. Selector Switch

8. Castle key interlock

The operating mechanism box conforms to IP 55 standard which

makes it dust and water proof. There is provision for heat sensor and

heater to keep the temperature constant.

The figure 5.2 shows a circuit diagram of motor operating mechanism.

FIG 5.2 CIRCUIT DIAGRAM OF MOM BOX

57

5.2.3.1 Ganging

Ganging is operating a set of disconnectors at the same time, i.e.

in a 3-phase disconnector system, the three disconnectors of three phases

are operated from the motor operating box.

In motor operated disconnectors, ganging is very common. Ganging can be

established in two ways.

• Mechanical Ganging

• Electrical Ganging

Mechanical Ganging:

All poles of the disconnector / earthing switch are coupled together

by means of mechanical linkages and one common operating mechanism

may be motor / manual is employed to operate the whole equipment. This

method of operation is called as mechanical ganging. The linkage device is

a tandem pipe.

Electrical Ganging:

In this case each pole of the disconnector / earth switch is

provided with independent motor operating mechanism. Out of which one

MOM will act like master control and the rest be follower controls. All the

poles of the switch can be operated simultaneously from the master control

cubicle. However, independent operation of each pole is also possible from

their respective motor operated mechanism (MOM) boxes, keeping the

gang selector switch in independent mode.

58

5.2.3.2 Interlocking

Interlocking is the mechanism which prevents the simultaneous operation

of earth switch and the disconnector switch. Similar to ganging, there are

two ways implement interlocking.

• Electrical Interlocking

• Mechanical Interlocking

Electrical Interlocking:

Electrical interlocking is done by connecting the auxiliary contacts

of various equipments in series to the control circuit of the present switch,

to enable the motor / manual operation only when all interlocking

requirements are fulfilling. To operate the disconnector manually, the

selector switch has to be set to manual position and then the solenoid

interlocking is disabled by a key interlock and then a crank handle is used

to operate the disconnector.

Mechanical Interlocking:

Mechanical interlocking is done by interdependent groove-cam

and projected shaft arrangement to block mal-operation of disconnector

and earthing switch simultaneously and also to have safety even in cases of

failure in electrical interlocking. Interlocking cams are fitted with TOM of

main switch and earth switch. Interlocking shaft/rod with threading on

both ends are given to allow the increase and decrease of rod length,

thereby allowing proper and 100% entry in the interlocking groove.

5.3 TESTING:

With so many electrical product safety standards currently in use

and many civil and legal actions pending in various courts around the

59

world, electrical safety testing is more critical than ever to ensure that all

products are safe before they reach the user. Fortunately, the majority of

manufacturers are fully aware of the hazards associated with electrical

equipment and the ramifications of non-compliance with relevant safety

standards or test house agreements.

Electrical safety tests can be roughly divided into two areas:

• Type tests or Conformance tests

• Routine Production tests or Routine tests

Those tests that are carried out during the approvals process by test

houses are known as type tests and those that are carried out at the end of

each production line by the manufacturer are known as routine production

tests.

For type tests, a product is subjected to tests and evaluations in

accordance with a specific product safety standard. For production tests, a

manufacturer can select a few tests, ensuring that each product is subjected

to those tests in accordance with its own procedures. Most manufacturers

choose four primary product safety tests to be routine at the end of the

production line. These include power frequency voltage test, main circuit

resistance, mechanical operation, and visual & dimensional check.

These tests are designed to ensure that the user does not get

electrocuted or otherwise hurt by operating a piece of equipment that has

hazardous voltages or high fault current as a result of electrical fault. This

chapter looks at the fundamentals behind each test and analyzes the

reasoning behind each test, as well as discussing appropriate limits and

equipment.

60

5.4 Type Tests

Conformance testing or type testing is testing to determine

whether a product or system meets some specified standard that has been

developed for efficiency or interoperability.

To aid in this, many test procedures and test setups have been

developed, either by the standard's maintainers or external organizations,

specifically for testing conformance to standards. Conformance testing is

often performed by external organizations, which is sometimes the

standards body itself, to give greater guarantees of compliance. Products

tested in such a manner are then advertised as being certified by that

external organization as complying with the standard. Service providers,

equipment manufacturers, and equipment suppliers rely on this data to

ensure Quality of Service (QoS) through this conformance process.

In electrical engineering, some countries and business

environments require that a product meet certain requirements before it

can be sold. Standards for electrical products written by standards

organizations such as IEEE, IEC, and IS, etc., have certain criteria that a

product must meet before compliance is recognized. In countries such as

Japan, China, Korea, and some parts of Europe, products cannot be sold

unless they are known to meet those requirements specified in the

standards.

Usually, manufacturers set their own requirements to ensure

product quality, sometimes with levels much higher than what the

governing bodies require. Failure levels are usually set depending on what

environment the product will be sold in. For instance, test on a product for

used in an industrial environment will not be as stringent as a product used

in a residential area. A failure can include insulation breakdown, arc

formation, and irregular behavior.

61

There are three main types of compliance test for electrical

services; emissions tests, immunity tests, and safety tests. Emissions tests

ensure that a product will not emit harmful interference by electromagnetic

radiation and/or electrical signals in communication systems. Immunity

tests ensure that a product is immune to common radio signals and

Electromagnetic interference (EMI) that will be found in its operating

environment, such as electromagnetic radiation from a local radio station

or interference from nearby products.

Safety tests ensure that a product will not create a safety risk from

situations such as a failed or shorted power supply, blocked cooling vent,

and power line voltage spikes and dips. A disconnector being an electrical

product is also subjected to many various compliance tests.

The various tests conducted are listed below

• Di-electric tests

- Power Frequency withstand voltage tests

- Lightning Impulse withstand voltage test

- Switching Impulse withstand voltage test

• Radio Interference Voltage test

• Corona inception and extinction test

• Measurement of resistance of main circuit

• Temperature rise test on main contacts

• Short time current and peak withstand current tests

• Mechanical Endurance & Terminal load test

• Verification for protection – IP 55 on ‘MOM/BOM’.

62

6. CONCLUSION

This study project discusses about High Voltage Disconnectors or simply

Disconnectors. Disconnectors are non-load switching devices which

disconnect a sub station from a power source for the sake of maintenance

and repair. When they are in closed position, they act as current carrying

devices and have to withstand heavy currents.

The project also covers the three types of disconnectors. They are

horizontal centre break disconnector, double-break disconnectors,

pantograph disconnector. The design, constructional features, assembly,

operation, testing of 440 kV disconnectors have been discussed in detail,

concentrating heavily on horizontal centre break disconnector, double

break disconnectors, and pantograph disconnectors which are widely used

in 440 kV power system.

During the course of this project, a deep insight into the types of

disconnectors are studied in detail and types of tests conducted on

disconnectors are mentioned.

We sincerely thank Siemens Ltd. (Hyderabad works) for giving us this

opportunity to do a mini-project in their company and we are proud to say

that we have found this industrial oriented mini-project was really useful

to get acquainted with various industrial processes, equipment involved in

manufacturing, different designs and testing techniques.

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BIBLIOGRAPHY

1. Power Systems by J.B. Gupta.

2. High Voltage Engineering Fundamentals 2nd edition by E. Kuffel,

W.S. Zaengl, J. Kuffel.

3. IEC 600694 Common specifications of High Voltage Switchgear

and Protection.

4. IEC 60060 – 1 High Voltage Dielectric Tests.

5. IEC 62271 – 102 High voltage alternating current circuit breakers.