Visit on substation Report

8/13/2019 Visit on substation Report

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Contents

1) Introduction1

2) Equipment details. 4

3)Padmanabah nagar sub-station (66/11 KV).6

4) Single line layout of the substation6

5) Earthing mat7

6) Lighting arrester.7

7) Isolators....8

8) SF6 circuit breaker.9

9) Transformer10

10) CTR fire protection system.12

11) Auxiliary transformer...13

12) Control room.13


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Introduction

Substation

The substation consists of the following essential equipments:

Incoming lines

Outgoing lines

Control room (control and protection panels)

Transformers (main power transformer and auxiliary transformer)

Circuit breaker, isolators, relay and metering panels

CTs, PTs, power cables and control cables

Station service equipment such as lighting arresters, auxiliary battery supply

Compressed air system

Station earthing system

Communication equipment such as carrier equipment telephone system etc

Classification of types of substation depends on various factors in which the major factor is

Based on voltage level:

A substation is named in accordance with its higher voltage level.

Example: a 66/11 KV A.C substation higher voltage level of 66 KV. Standard Indian voltages

Refer to normal power frequency phase to phase A.C voltages.

Types of substation for voltages more than 66 KV and above

Conventional outdoor:

Substations (open terminal air insulated type) in which busbars and live parts can be seen

with the naked eye.

Gas insulated metal enclosed substation:

Substation in which various equipments are with alluminium enclosures filled with gas for

internal insulation, such substations can be generally indoor.

Electrical substation has several indoor and outdoor equipment Each equipment has acertain functional requirements. The choice of the equipment depends on technical

considerations, rated voltage, rated MVA and the type of substation.


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Various Equipment Details:

Equipment Function Remarks

Bus bars Various incoming and

outgoing circuits are

connected to bus bars.

They receive power from

incoming circuits and deliver

power to the outgoing

circuits.

Flexible ACSR or all

alluminium stranded bus bars

supported from the two ends

by strain insulators.

Surge arrestor

(lightning arrestor)

Surge arrestors discharge

the over voltage surges to

earth and protect the

equipment insulation from

switching surges and

lightning surges. (The word

surge refers to impulse in

transmission and

distribution.)

Connected generally between

phase conductors and ground

Located as the first equipment

as seen from the incoming

over head line and also near

transformer terminals phase to

ground.

Isolators

(disconnecting switches)

To provide isolation from

the live parts for the

purpose of maintenance.

Located at each side of circuit

breaker.

Does not have any rating for

current breaking or currentmaking.

Earth switch Discharge the voltage on

the circuit to earth for

safety.

Mounted on the frame of the

isolators.

Located generally for each

incomer and each bus section.

Current transformer Stepping down the current

measurement ,protection

and control.

Protective CT

Measuring CT

Location decided by protective

zone measurement

requirements.Voltage transformer Stepping down voltage for

measurements, protection

and control.

Types

Electro magnetic

Capacitive VT (CVT)

Location on feeder side of

circuit breaker.


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OBSERVATION OF PART OF SUBSTATION

RAIN SHEDH

LIGHTNING ARRESTER

ARCING HORN

ISOLATOR

CABLE (XLPE)

SF6CIRCUITBREAKER

CT

AL.PIPES

LATTICS STRUCTURE POLE


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Padmanabah nagar sub-station (66/11 KV)

The 66/11 KV padmanabah nagar sub-station is located opposite one of the famous

landmarks of Bengaluru namely Devegowda (Indias former prime minister) petrolstation.The sub-station is one of the several 66/11 KV sub-station in Bengaluru. There are

total 40 nos. 66/11 KV sub-station in Bengaluru catering a load of 2000 MW which is 1/3rd

of power supply in Bengaluru. There are 10 nos. of 220/66 KV sub-station in Bengaluru.

Bengaluru follows a ring structure around the city which is one of its kind in India from which

several 66/11 KV supply is taken, this ring structure terminates at the same point where it

started. All equipment and system is earthed properly through GI strips of 25X6 mm and

150X6 mm via earth electrode which in turn is connected to earth-mat.

The sub-station is having two 66 KV incoming supply. These two incoming supply is coming

from Subramanyapura- 1 & 2 sub-station through XLPE ( Cross Linked Polyi-Ethylene)

cables. These cables are 660sq.mm, 3-phase single core copper cable. These cables aredesigned according to required voltage, creapage and rain .At present the station bay (area

under an over head structure) is being extended to provide another 66 KV line to serve as

another alternate 66 KV source since both the present feeders are from the same station.

The present two incoming feeders are used alternatively (one at a time). The station peak

load is 24 mega watts and handle about 3,25000 units every day.

Single line diagram of 66 / 11 KV substation :


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Earthing Mat

The earth mat is designed after the procurement of land area. The land is excavated by 1m

deep. After the excavation the galvanized iron rods are laid in latitudinaly and longitudinally.

In this sub-station the earthing mat design is done by KPTCL using software. During

construction of the earth-mat charcoal and sand with water is added to lower the resistivity ofsoil. The dimension of GI material is 25X2 mm and 150X6 mm. The main criterion to design

the earth-mat is to find soil resistivity. The soil resistivity varies widely and depends on the

nature of soil. The main purpose of designing earthing system is to protect both human and

electrical system from electric hazards. Humans are very vulnerable to the effects of electric

currents. Even a current of 0.1 A is lethal at power frequency. The purpose of earthing is to

provide:-

To provide low impedance path to current.

To ensure living beings in the vicinity of sub-station are not expose to unsafe

potentials.

To retain system voltages at reasonable limits.

To provide an alternating path for induced currents there by minimize electric

noise.

Lightening Arrester

The lightening or surge arresters (L.A) used in the sub-station is rod gap type. These are

used for the protection of power system

equipments. The surge arrester used here is of

45 KV. The XLPE cable coming from

Subramanyapura sub-station terminates here

through L&T-type clamps. The surge arresters

are mounted on the platform which is earthed by

GI strip and through the earthed electrode it is

connected to earthing-mat.

The XLPE cables terminating on these arresters

are earthed by another single core cable on to

the GI strip. The conductor used from LAs to

line bus is ACSR wolf conductor. The working

Formula to find the rating of surge arrestor is:-

Rating :( 66/3) = 38 KV


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Isolators

The isolator is 66 KV incoming line Gang Operating Switch (GOS). The main purpose of the

isolator is to carry out maintenance work after line clearance. The isolators are mounted on

the lattice structures and are earthed by GI strips to earth electrode which in turn is

connected to earthing mat. The first line isolators are always provided with the earth orgrounding switch. This grounding switch is provided to carry out maintenance work.

Whenever there is any work required to carry out in the system we put operate the earth

switch so that the whole system will be at ground potential. This earth switch is provided in

both of the sub-stations i.e padmanabah and Subramanyapura. In some isolators there is

mechanical interlocking provided so that the earth switch cannot be operated when the

system is in line. If this is done than the whole system will be at high risk and havoc is

created. There are two types of isolator:-

Single Break Isolator:

This isolator is used where the line current is less than 200 A.

Double Break Isolator:

This isolator is used when the line current is more than 200 A. The isolators are always

designed on fault current.


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SF6 Circuit Breaker

The 66 KV SF6 circuit breaker comes after the isolator. In this breaker SF6 (Sulphur

Hexafluoride) gas is used. In this breaker the arc quenching is done by SF6 gas whereas the

air is used for tripping and spring loading purpose. SF6 gas is considered to be very good

arc quenching property. The pressure maintained in SF6 cylinder is 6 kg/cm2

and in aircylinder is 15 kg/cm2. There is one compressor installed inside the breaker cabin whenever

the pressure of air drops below 15 kg/cm2 it starts automatically. There are two types of SF6

breaker:-

Single break

This is used for 66 and above. In this the female contact is fixed and male contact is

movable and is non-electric conductor.

Double break

This is used for 220 KV and above. In this the live part is kept at ground potential.

The tripping time in this breaker is 10-20 ms and charging time is 100 ms. The top mostpart used for connection and central portion hold conductor called interrupter. The

pressure inside interrupter is around 6kg/cm2.There are two DC coils present one is for

tripping and other is for back protection (in case the first one fails to operate). One of the

several advantages of using SF6 is that the loss of gas is very minimum and it can go

upto 2 years without stopping.

Some of the safety features of this breaker are as follows:-

a) DC failure safety (breaker trips itself whenever dc fails and fails to obey any command.

b) Air pressure below 12 kg/cm2 cylinder automatically starts.

c) Interrupter is designed at 6 kg/cm2.

d) Tripping and charging is done by quick action

spring.


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Transformer

There are two one of 16\20MVA and another of 31.5 MVA Dyn11 vector group 66/11kv class

transformers. Feeding supply through double circuit of ring main

Observation

Transformer rating 16/20 MVA (66/11 KV)19/31.5 MVA(66/11 KV)

Vector group DYn11

Cooling system16 MVAONAN TYPE20 MVAONAF TYPE

Bushing Oil impregnated condenser bushing (66 KV)

Cooling fans 4 nos

Conservator tank2 nos

For active partFor OLTC

On load tap changer MR type33 rev = 1 tap

Breather Silica gel breather

Protection of Transformer

The type of a protective gear for a Transformer depends upon several factors such as:

Type of Transformer

Size of Transformer

One of the Common Protection is Buchholz Protection

Buchholz Protection

Buchholz Relay is installed between the Transformer and the Conservator tank and is used

to give warning in case of less severe internal faults in oil immersed Transformer and to

disconnect the Transformer from the main supply in case of severe Internal faults. It is

practically used on all oil immersed Transformer having rating more than 750kva.It is used in

conjunction with some form of electrically operated protective gears because it provides

protection against Transformer Internal faults and does not respond to external bushing or

cable connection faults.


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CTR Fire Protection system

Transformer is also protected from fire during any abnormal fault condition. Well adequate

clearance is maintained between the two transformers in the substation.

Main equipment used for this is the water emulsified fire extinguisher which takes care of theabnormal conditions. During these fault conditions CTR has equipment which does not allow

the oil passage from the top portion of the conservator tank when it senses any abnormal

temperature difference.

Various monitoring conditions employed in CTR fire protection scheme

Differential relay trip

Pressure relief valve tripBuchholz Protection

Fire detector trip

Transformer trip

Line fault differential trip

Line fault PRV

Lamp test


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Auxiliary transformer

Back up transformer is also maintained in the substation through which supply is fed to the

control panel equipments and for lighting purpose.

Specifications of the auxiliary transformer: 410/55-0-55 V/ 500 VA

Control room

Monitoring of the entire substation can made from the control room. In this all the preliminary

actions for the improvement or for any fault clearing conditions can be monitored.

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