Sub Station Design

8/3/2019 Sub Station Design

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SIEMENS

PRESENTATION

ONSUBSTATION DESIGN

By

Yuvaraj Patil

I&S/WR


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SUBSTATION DESIGN

WHAT IS THERE IN SUBSTATION DESIGNING ??

SLD

EQUIPMENT LAYOUT

BUSBAR ARRANGEMENTFAULT LEVEL

TYPE OF CONSTRUCTION

CREEPAGE AND CLEARANCE

GROUNDING & LIGHTNING PROTECTION

SAFETY INTERLOCKSOTHERS, e.g. LIGHTING AND CIVIL


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SUBSTATION DESIGN CRITERIA

FOLLOWING STUDIES ARE PERFORMED TO ESTABLISH THE

DESIGN CRITERIA FOR A SUBSTATION

1. LOAD FLOW STUDIES :

- To determine the current carrying requirements of new s/s.- To determine the continuous and Emergency rating of

equipment

2. S.C.CALCULATION :

- To permit the equipment to without damage, severe thermaland mechanical stresses of S.C. currents.

- To provide adequate interrupting capability in CBs, strength

in post insulators

- Setting of protective relays


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SUBSTATION DESIGN CRITERIA

3. TRANSIENT STABILITY STUDY :

Following factors affects the Stability of System.

- Severity ofFault

- Speed with which fault is cleared

- Ties between the Machine and the System after the fault are

cleared ( Which may weaken the system by operating more

than one line due to not operation of primary relaying )

4. TRANSIENT OVER VOLTAGE STUDY :

- It is required to protect the equipments from Lightning Stroke

and Switching Transient.

-*-


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SUBSTATION ARRANGEMENT ASPECTS

1. System Security :

- The ideal s/s is one where each circuit is controlled byseparate CB with facility for replacement of bus bar OR CB inthe event of fault or during maintenance.

- Double Bus Bar system with Double CB arrangement is ideal.

2. Operational Flexibility :

- For efficient loading of Generators it is necessary to controlMVA and MVAR loading under all condition

3. Simplicity of Protection Arrangement :

- Where greater no of CB has to be tripped during faultcondition, protection arrangement becomes more complex.

JERP is best example of complex Protection !!


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SUBSTATION ARRANGEMENT ASPECTS

4. Ability to Limit the S.C. Levels :

- Any arrangement which incorporates means of providing a S/S

into Two separate sections is suitable to Limit S.C levels.

5. Maintenance Facilities :

- Arrangement shall be suitable for the Planned or Emergency

Maintenance .

6. Ease of Extension ::

- To add new bays there shall be space and expansion facilities.

7. Site Considerations :

- Where the area is limited, simple arrangement with least no of

CBs.


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Considerations for Choice of Busbar Arrangement

A number of factors are to be considered while finalizing the Layout

and Switching arrangements of S/S.

Importance of Substation

Reliability

Redundancy

Economics and availability of finance

Availability of Space and Right Of Way for approaching

lines

Future Expansion


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LineIsolator

Bus

Bus-Isolator

Circuit-breaker

Earthing-switch

Protection-zone,busbar

Protection-zone,line/trafo

Line 2Line 1

Single Bus System- Primary Components,

Protection Zone

Current

Transformer

PotentialTransformer

Bus-EarthingSwitch

Bus-PotentialTransformer

Wave

Trap

LineIsolator

Earthing-switch

Wave

Trap

Surgearrester

Transformer


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Main & Transfer Bus ArrangementMain Bus

x

Transfer Bus coupler

A Transfer Bus Coupler & All feeders need one additional isolator.

In Thermax Project we are using this arrangement

Transfer Bus

x

Line 1

LineIsolator

Earthing-switch

WaveTrap

Surgearrester

TransferIsolator

x

Line 2

LineIsolator

Earthing-switch

WaveTrap

Surgearrester

Transfer

Isolator

x

Line 3

Line

Isolator

Earthing-

switch

Wave

Trap

Surgearrester

TransferIsolator

CT CT CT CT


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Ring or Mesh SystemLine 1

Line 2

Transformer 1 Transformer 2


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Bus-disconnect

Circuit-breaker

CT

VT

Line-disconnect

Earthing switch

Bus Section-isolatorBus BBus A

Surge arrester

Earthing switch

Single Bus with sectionaliser System- Primary

Components,

Over-lapping Protection Zone

Bus PT 1 Bus PT 2

To improve Reliability bus section isolator/CB is introduced


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Bus-Isolators

Circuit-breaker

CT

Bus I

Bus II

Bus-coupler

Double Main Bus System

or Main & Reserve Bus system

LineIsolator

Earthing-switch

Transformer

LineIsolator

Earthing-switch

WaveTrap

Surgearrester

Line 1

Earthing-switch

WaveTrap

Surgearrester

Line 2

Bus-PT -I

Bus-PT -II

Bus-Earthing-I, II


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Bus-Isolators

Circuit-breaker

CT

Bus I

Bus II

Bus-coupler

Double Main & Transfer Bus

Arrangement (DMT)

LineIsolator

Earthing-switch

WaveTrap

Surgearrester

Line 1

Bus-PT -I

Bus-PT -II

Bus-Earthing-I, II

Earthing-switch

WaveTrap

Surgearrester

Line 2

TransferBus-coupler

TransferIsolator

Almost all PGCIL 220kV substations use this arrangement


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Bus A

Bus B

Q0 41

Q0 42

Q0 11

Q0 13

Q0 12

For future use

Bushing

Bushing

One and a Half Breaker

Arrangement

Almost all PGCIL 765kv,400kV substations use this arrangement


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2000/1/1/1A

Core Likeline 417

Three Main & Transfer Bus Arrangement

Practiced in Europe, Germany


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245 kV Outdoor switchyard (AIS) Double busbars, classical layout

1 Bus I 3 Bus-disconnector 5 CT 7 Line-disconnector with built-on earthing switch

2 Bus II 4 Circuit-breaker 6 VT 8 Surge arrester

245kV Switchyard Layout

Almost all PGCIL 220kV substations use this arrangement


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SUBSTATION DESIGN CONSIDERATIONS

1. FAULT LEVEL :

Expressed as MVA or kA and duration of 1-3 Sec.

Depends on source impedance

All CBs are to be rated for fault level

Earth Switches for making fault level

- All Bus bars, bus supports to be designed to withstand forcesdue to S.C

2.SAFETY CLEARANCES :

3. STRUCTURE :

Why is it required ?

To support and install Buses, electrical equipment and terminatetransmission line conductors.

The structures may be of steel, RCC or wood

They need foundation according to soil condition at site


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Design of Structures are affected by :

- Phase clearance

- Ground clearance

- Length and weight of buses and other equipment.

Design Load on Girders shall include :

- Conductor tension

- Earth wire tension

- Weight of Insulators and Hardwares

- Erection load ( approx. 350 kg)

- Weigh of man & tools to work ( aprox. 200kg)- Wind load

- Impact load, if any during operation of equipment.

- Walkway if any.

( BSP Project we are providing the same)


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4. Recommended Standard Bay Widths :

a. 400kV feeder Bays - 27m

b. 400kV Transformer Bays - 20m ( per phase)

c. 220kV Feeder Bays - 17m

d. 110kV Feeder Bays - 10m

e. 110kV Transformer Bays - 10m

f. 66kV Bays - 8m

g. 22kV Bays - 3.8mh. 11kV Bays - 3.5m


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Normally adopted phase spacings are :

Sr. No. Voltage Level (kV) Spacing (m)

1 11/22 1.3

2 33 1.5

3 66 2.0 to 2.2

4

110 2

.4

to3

.0

5 220 4.5

6 400 7.0


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BUS DESIGN

Present day trend is to use Rigid bus rather than strain bus due to

can be constructed at lower profile.

are aesthetically pleasing.

corona level is lower.

1. Construction of Rigid Bus : Aluminum bus materials used for rigid bus may be of different

shapes.

They may be round tubing's, channels, angles or integral web

designs.

Round tubing used in all voltage levels.

Square/channel tubing is used only at lower voltages.

Angle bus used only at distribution voltages.

Integral web bus is structurally strong and is used for high current and

long spans generally at lower voltage.


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BUS DESIGN

Design considerations of Rigid Bus :

Bus must carry the expected maximum load current withoutexceeding the temp. limit .

The capacity of bus shall be checked for max. temp. under S.C.

conditions.Shall be designed to take vibration induced by the action of

50Hz current.

Shall be designed to take the vibration due to wind flowingacross the tubing.

It should withstand the S.C. force.

for HV and EHV S/S the diameter of bus should be checked forcorona discharge.

The bus support system must be capable to to take weight oftubing, damping material, wind on tubing, S.C. force calculated.


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BUS DESIGN

2. Design considerations of Strain Bus :

Widely used in most of the station due to ease of construction.

Even in station where Rigid bus is predominant, some spans willbe invariably of strain bus construction.

The design followed is based on simple sag-tensioncalculations.

The down drops from strain bus appear as a concentrated load.

Depending on length and weight of dropper, tension on bus willvary considerably.

Where bundled conductors are used in strain bus, the type of

spacer may have an influence on resulting tension. If rigid spacers are used, then during S.C., the two conductors

will attempt to draw together and cause increases tension onstrain bus


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ACCESSORIES REQUIRED FORBUS CONSTRUCTION

RIGID BUS :

1. BPI

2. Aluminium Tubular pipes for bus

3. Welding Sleeves of equivalent dia for Al Bus.

4. BPI clamp for fixing tubular pipe to the insulator5. Inter connector for Al tube to strain Bus

6. Corona bells for the free ends of right bus.

STRAIN BUS :

1. Insulator strings2. ACSR conductor of right choice

3. Hardware fittings for tension points.

4. Arcing horns

5. Corona rings


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ACCESSORIES REQUIRED FORBUS CONSTRUCTION

6. Sag compensating spring.

7. Suspension clamps with accessories for jumper connection

points.

8. Rigid or flexible spacers ( For bundle conductor bus)

9. Parallel Groove clamps (PG Clamps) suitable for the ACSR forjumper and dropper connections.

10. Tee Clamps for droppers. (With suitable sizes).

11. Clamp to connect droppers, jumpers and interconnections to

the equipment and on BPI


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SUBSTATION EARTHING

Purpose :

In ungrounded system, it will be inherently coupledcapacitively to the earth th system capacitance. During groundfault, the charging current will rise to 3 times the Zerosequence current, develops high value of voltage.

so earthing is required to

1. Limit the transient overvoltages caused by restricting the

ground current.2. Safety to the personnel working in the maintenance.

3. Fast and selective clearing of ground fault to limit the damageto the equipment.


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SUBSTATION EARTHING

Following steps are involved in Design of Earthing System.

1. Soil investigation.

2. Determination of maximum ground current

3. Preliminary designing of grounding system

4. Calculation of resistance of grounding system

5. Calculation of maximum grid potential rise.

6. Calculation of step and touch voltages.

7. Correction of preliminary design.

A continuous earth conductor is placed around the

perimeter of yard to enclose as much ground as possible toavoid current concentration.

Within the grid conductors are laid in parallel lines and atuniform spacing along the rows of structure and equipment.


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SUBSTATION EARTHING

The earthing material should have

High conductivity

Low underground corrosion

GI material is used for earthing and size of conductor should be

such that

It has thermal stability to flow the ground fault current

It should last at least for 50 years without causing break in the

ground circuit due to corrosion

It should be mechanically strong.


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INSTRUMENT TRANSFORMER

Instrument Transformers are used to provide the exact

proportion of the high voltage and current within the substation

at a level suitable for metering, relaying and control.

Voltage Transformers :

VT may be of Electromagnetic or Capacitor type.When high level of accuracy is required then Electromagnetic

type is used.

All voltage transformers are required to comply with one of the

classes in Table 8.1.


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VOLTAGE TRANSFORMER

For protection purposes, accuracy of voltage measurement

may be important during fault conditions, as the system voltage

might be reduced by the fault to a low value. Voltage

transformers for such types of service must comply with the

extended range of requirements set out in table 8.2


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VOLTAGE TRANSFORMER

Voltage Factors :

The value Vfin Table 8.2 is an upper limit of operating voltage,expressed in per unit of rated voltage. This is important for correct relayoperation and operation under unbalanced fault conditions onunearthed or impedance earthed systems,. Voltage factors, with the

permissible duration of the maximum voltage, are given in Table 8.3.


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VOLTAGE TRANSFORMER

Protection of Voltage Transformers

o Voltage Transformers can be protected by H.R.C. fuses on the

primary side for voltages up to 66kV. Fuses do not usually have

a sufficient interrupting capacity for use with higher voltages.

o In some cases protection on the primary is omitted. The

secondary of a Voltage Transformer should always be protected

by fuses or a miniature circuit breaker (MCB).


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CURRENT TRANSFORMER

CURRENT TRANSFORMER

The current transformers may be either of bushing type or wound

type.

CT should be selected with a rating 25% greater than the max

current that is likely to flow during normal operation.Protective CT should have high saturation factor.

The secondary circuit must not be interrupted while the primary

winding is energized. The induced secondary e.m.f. under these

circumstances will be high enough to present a danger to life and

insulation.Protection class current transformers must retain a reasonable

accuracy up to the largest relevant current. This value is known

as the accuracy limit current

The ratio of the accuracy limit current to the rated current is

known as the 'accuracy limit factor


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CURRENT TRANSFORMER

The accuracy class of protection current transformers is shown in Table

Class PS Current Transformers

The classification of Table 5 is only used for overcurrent protection

PS commonly used with unit protection schemes

Knee point is a key factor in the PS class CT


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POWER TRANSFORMER

RATINGS :

Transformer ratings shall be such that the transformer can

deliver its rated current under steady loading conditions without

exceeding the limits of temperature-rise specified in IS : 2026 (

Part II ) - 1977* assuming that the applied voltage is equal to therated voltage and that the supply is at rated frequency.

SERVICE CONDITIONS :

Transformers complying with IS-2026 are suitable for operation

continuously at their ratings, provided the temperature of thecooling air or water does not exceed any of the reference

ambient temperatures specified


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POWER TRANSFORMER

kVA Ratings:

kVA ratings for three-phase transformers are given in below table

For single-phase transformers intended for use in three-phase

banks, the kVA ratings are one-third of the values in Table 2.


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POWER TRANSFORMER

Operation at Other than Rated Voltage :

- A transformer built in accordance with IS-2026 may beoperated at its rated kVA at any voltage within +/- 10 percent ofthe rated voltage of that particular tap.

- The transformer shall be capable of delivering rated current ata voltage equal to 105 percent of the rated voltage.

Operation at Rated Frequency :

The frequency for A transformer built in accordance with IS-2026 standard shall be 50 Hz with tolerance of +/- 3 percent.

Temp Rise:

The transformer shall confirm to the requirements oftemperature rise specified in IS : 2026 (Part II)


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POWER TRANSFORMER

Insulation Levels :

The insulation levels shall be in accordance with IS : 2026 (Part

III)- 19777.

Terminal markings, tappings and Connections :

The terminal markings, tapings and connections shall be in

accordance with IS : 2026 ( Part IV )-1977

Requirement with regards to Ability to withstand S.C.

Transformers shall be designed and constructed to withstand

without damage the thermal and dynamic effects of external

short circuit under the conditions specified in IS:2026.


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POWER TRANSFORMER

CRITERIA FOR SELECTION OF POWER TRANSFORMERS

( ABOVE 1600kVA)Ratings :

o The secondary no-load voltage should be specified 5percent more than the nominal voltage to compensate the

transformer regulation partly.o For transformers requiring to be operated in parallel, the voltage

ratio should be selected in accordance with guidelines given inIS : 10028 ( Part 2 )-1981*.

Taps :

o On-load tap changers on HV side should be specified,

wherever required.o The total number of taps should be 16 in steps of 1.25 percent..

Off-circuit taps, when specified, should be in the range of 2.5percent and +/- 5 percent provided on the HV side.


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POWER TRANSFORMER

Connection Symbol :

o The preferred connections for two winding transformers up

to 66 kV high voltage ( HV ) side rating are delta/star ( Dyn ) and

star/star ( YNyn ). For higher voltages, connections star/star

(YNyn) or star/delta ( YNd ) may be preferred.o The selection of connection group should be made taking into

consideration the requirements of parallel operation with other

transformers

Impedance :

o The transformer impedance is decided taking into Considerationthe secondary fault levels and the voltage dip.

o typical impedance values are given IS : 2026 ( Part 1 )-19777.


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POWER TRANSFORMER

Termination Arrangement :

o Primary and secondary terminals may be bare bushings,

cable boxes or bus trunking depending upon the method of

installation.o It is preferable to specify disconnecting chamber between

transformer terminals and cable box to facilitate disconnection of

transformer.


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OTHER DEVICES AND EQUIPMENTS

Due to the time constraint following devices/equipments

are not covered in detail !!!

Circuit Breakers

Isolator and earth Switch

LABattery and battery Charger

ACDB

DCDB

AHU for Control room

Control & Relay Panel


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SIEMENS

THANK YOU

For your Patience !

Sub Station Design

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