STUDY OF 132/33KV SUBSTATION, MACHILIPATNAM

An industrial oriented mini project report submitted in partial fulfillment for the award of the

degree “BACHELOR OF TECHNOLOGY” in EEE by p.somasekhar(08mq1a0252) under the

esteemed guidance of

Department of E.E.E

SVIET

JNTUK

Acknowledgement

We wish to express our profound sense of gratitude to sri S.E,substation,gunadala for giving this wonderfull opportunity.

We grateful acknowledge the help&encouragement received from sri A.A.E,substation,machilipatnam for their valuable suggestions&cooperation in completing this work.

Our heartiest thanks to all faculty members especially sri A.A.E,substation,machilipatnam,who had guidedto complete project work.

Abstract

The main objective of substation is to distribute the electric energy generated in the generating plants.The other purpose of substation is to increase or decrease the voltage level to required range and then distributed.

The 132/33KV machilipatnam substation receives 132KV from pamarru&konikepudi.Now the receiving voltage is stepdown to 33KV by using station transformers&other equipments.Now 33KV is transmitted to challapalli,machilipatnam,sarada nagar&pedana.

List of symbols

Name symbols

1.Isolator

2.current transformer

3.Circuit breaker

4.station transformer

5.power transformer

6.potential transformer

List of figures

Index

Introduction to substation Layout of substation Major equipment in substation Protection of transformers Protection of feeders Batteries Earthing of substation Conclusion References

Introduction

Substation:

The assembly of apparatus used to change some characteristics(voltage AC to DC) of electric supply.

Machilipatnam Substation:

The 132/33KV machilipatnam sub station is located in gollapalem road,machilipatnam in an area of about 5 acres of land.It is capable of delivering 63 MW of power requirement of machilipatnam town&Krishna Dist. It consists of 2 No’s 132/33 KV power transformers, 3 No’s 132KV feeders,& 5 No’s 33KV feeders to meet the load of the machilipatnam, surrounding municipality& other rural villages.

Date of charging of substation:132KV on 17-12-1993.

Sources of supply:

The 132/33KV machilipatnam substation receives power from the 220KV SS,Gudivada via 132KV Pamarru-Machilipatnam double circuit line. The sub station is also connected to private generating station M/S RVK energy through 132KV Konikepudi single circuit feeder.

MAJOR EQUIPMENT IN SUB-STATION:

The equipment used in sub-stations are mainly depends upon the type of sub-station, service requirement and the degree of protection desired. However, in general, a sub-station has the following main equipments.

Circuit breakers

Current transformers

Potential transformers

Lightning arresters

Power transformers

Station transformers

isolator

Circuit breaker:

The purpose of C.B. is to open the circuit under fault conditions.

The C.B. used in 132kv substation is SF6 C.B

PARTICULARS OF C.B:

Make:ABB

Type:ELF SF2-1[r]

Voltage:145kv

Normal current:2000A

Mass:1750kg

CURRENT TRANSFORMER:

The purpose of C.T. is to step up the current to known ratio.

PARTICULARS OF C.T:

Make:ABB

Type: TMBRI 145

Voltage:145kv

Primary Normal current:600-300-150/1-1-1A

Mass:400kg

Burden:15VA

Adopted C.T. ratio:600/1A

POWER TRANSFORMERS:

These are used to increase or decrease the voltage level.

Power rating:31.5MVA

Voltage rating:132/33kv

ISOLATOR:

Isolator is knife switch & design of open a circuit under no-load condition PARTICULARS OF ISOLATOR:

Make:ELPRO international limited

Type:DBR

PARTICULARS OF POTENTIAL TRANSFORMER:

Make:Crompton Greaves

Type:VE OT:145-275-650WO[W-1169]

Voltage:145kv

Mass:365kg

Burden:500 VA

Station transformer:

The purpose of station transformer is to stepdown the voltage to 440v and it is used in substation

LIGHTING ARRESTER:

The purpose of L.A. is to protect the system from high voltages.Here 3 L.A. s are used in 3 phases.

System voltage:132kv&

rated voltage:120kv

PROTECTION OF TRANSFORMERS

Differential relay protection:

Differential protection is a very reliable method of protecting generators, transformers, buses, and transmission lines from the effects of internal faults.

In a differential protection scheme in the above figure, currents on both sides of the equipment are compared. The figure shows the connection only for one phase, but a similar connection is usually used in each phase of the protected equipment. Under normal conditions, or for a fault outside of the protected zone, current I1 is equal to current I2 . Therefore the currents in the current transformers secondaries are also equal, i.e. i1 = i2 and no current flows through the current relay. 

If a fault develops inside of the protected zone, currents I1 and I2 are no longer equal, therefore i1 and i2 are not equal and there is  a current flowing through the current relay.

Over current and earth fault protection:

 The over current protection is needed to protect the transformer from sustained overloads and short circuits. Induction type over current relays are used which in addition to providing overload protection acts as back up relays for protection of transformer winding fault.

The available 132/33KV,31.5 MVA power transformers are provided with over current& directional earth fault relays on both HV&LV sides

Bucholtz relay protection:

Buchholz relay is a gas- actuated relay installed in oil-immersed transformers for protection against all kind of faults. It is used to gives an alarm in case of slow developing faults or

incipient faults in the transformer and to disconnect the transformer from the supply in the event of severe internal faults

It is installed in the pipe between the conservator and main tank as shown in fig11 below. This relay is used in oil-immersed transformers of rating above 750 kVA.

OPERATION

The operation of buchholz relay is as follows:

i. In case of slow developing faults within the transformer, the heat due to the fault

causes decomposition of some transformer oil in the main tank. The products of decomposition mainly contain 70 % of hydrogen gas. The hydrogen gas being light tries to go into the conservator and in the process gets trapped in the upper part of the relay chamber. When a predetermined amount of gas gets accumulated, it exerts sufficient pressure on the float to cause

it to tilt and close the contacts of mercury switch attached to it. This completes the alarm circuit to sound an alarm.

ii. If serious fault occur in the transformer, an enormous amount of gas is generated in

the main tank. The oil in the main tank rushes towards the conservator via the buchholz relay and

in doing so it tilts the flap to close the contacts of mercury switch. This completes the trip circuit

to open the circuit breaker controlling the transformer.

PROTECTION OF FEEDERS

Feeders play an important role in substation for transmitting the voltage from substation to consumers. So we can protect the feeders from faults. Mainly there are two methods used in substation for protection of feeders. They are

1.Distance protection

2.Backup protection

Distance protection:

The numerical distance protection schemes provided have the feature of fault locator where as static/electro mechanical are not having fault locator feature. It will show the location of fault in Kilo meters in the event of fault on line. Also,these relays service values like

Voltage,current,power etc. Different displays available in relays are mentioned under the section “Reading of Relays”. Distance relay clears the faults in ZONE-I(i.e., 80% of line)instantly. Balance 20% of the line will be cleared in ZONE-II i.e., with time delay, generally after 300ms.

2.Back up protection:

Some times it is possible for breaker to fail to trip upon action of a protective relay. This may result in tripping of all the breakers feeding the fault& result in wide spread block outs. To prevent such major disturbances LBB relay is provided in all the 132KV feeder/PTr panels. When breaker fails to trip on operation of relay,after elapsing the preset time in LBB relay,m it will extend the trip signal to other breakers connected to that bus,thus limiting the fault to local area.

When this relay acts it is necessary to isolate the faulty breaker before normalcy is restored