21-11-2012, 04:16 PM
132KV GRID SUB-STATION SITAPURA
132KV GRID SUB-STATION.docx (Size: 41.61 KB / Downloads: 61)
Definition of sub-station :-
“The assembly of apparatus used to change somecharacteristics (e.g. Voltage ac t o d c freq. p.f. etc) of electricsupply is called sub-station”
Introduction :-
The present day electrical power system is a.c. i.e. electricpower is generated, transmitted and distributed in the form ofAlternating current. The electric power is produce at the powerstation, which are located at favorable places, generally quiteaway from the consumers. It is delivered to the consumerthrough a large network of transmission and distribution. Atmany place in the line of power system, it may be desirable andnecessary to change some characteristic (e.g. Voltage, ac to dc,frequencyp.f. etc.) of electric supply. This is accomplished bysuitable apparatus called sub-station for example, generationvoltage (11KV or 6.6KV) at the power station is stepped up tohigh voltage (Say 132KV to 132KV) for transmission of electricpower. Similarly near the consumer’s localities, the voltage mayhave to be stepped down to utilization level. This job is againaccomplished by suitable apparatus called sub-station.
About the substation :-
The substation in 132kv sitapura.Rajasthan is one ofthe largest power grids in the state of Rajasthan and the northwestareaIndia.The most important of any substation is the grounding(Earthing System) of the instruments, transformers etc. used in
the substation for the safety of the operation personnel as well as
for proper system operation and performance of the protectivedevices.
An earthes system comprising of an earthing mat buried at asuitable depth below ground and supplemented with ground rodsat suitable points is provided in the substations. These ground theextra high voltage to the ground.As it is dangerous to us to gonear the instrument without proper earth. If the instruments arenot ground properly they may give a huge shock to anyone whowould stay near it and also it is dangerous for the costlyinstrument as they may get damaged by this high voltage.
Site Selection & Layout 132KV Substation :-
132KV Sub-Station forms an important link betweenTransmission network and Distribution network. It has a vitalinfluence of reliability of service. Apart from ensuring efficienttransmission and Distribution of power, the sub-station configurationshould be such that it enables easy maintenance of equipment andminimum interruptions in power supply. Sub-Station is constructedas near as possible to the load center. The voltage level of powertransmission is decided on the quantum of power to be transmitted tothe load center.
Selection of site :-
Main points to be considered while selecting the site for GridSub-Station are as follows:
i) The site chosen should be as near to the load center as possible.
ii) It should be easily approachable by road or rail for transportationofequipments.
iii) Land should be fairly leveled to minimize development cost.
iv) Source of water should be as near to the site as possible. This isbecause water is required for various construction activities(especially civil works), earthing and for drinking purposes etc.
v) The sub-station site should be as near to the town / city butshould be clear of public places, aerodromes, and Military /policeinstallations.
vi) The land should be have sufficient ground area to accommodatesubstationequipments, buildings, staff quarters, space for storageof material, such as store yards and store sheds etc. with roadsand space for future expansion.
vii) Set back distances from various roads such as National Highways,
State Highways should be observed as per the regulations in force.
viii) While selecting the land for the Substation preference to be
given to the Govt. land over private land.
ix) The land should not have water logging problem.
x) Far away from obstructions, to permit easy and safe approach
/termination of high voltage overhead transmission lines.
4.Equipment in a 132KV Sub-Station :-
The equipment required for a transformer Sub-Stationdepends upon the type of Sub-Station, Service requirement andthe degree of protection desired. 132KV EHV Sub-Station has thefollowing major equipments.
1) Bus-bar :-When a no. of lines operating at the same voltage have tobe directly connected electrically, bus-bar are used, it is made up ofcopper or aluminum bars (generally of rectangular X-Section) andoperate at constant voltage.
The bus is a line in which the incoming feeders come into and
get into the instruments for further step up or step down. The firstbus is used for putting the incoming feeders in LA single line.Theremaybe double line in the bus so that if any fault occurs in the onethe other can still have the current and the supply will not stop. Thetwo lines in the bus are separated by a little distance by a Conductorhaving a connector between them. This is so that one can work at atime and the other works only if the first is having any fault.
2) Insulators :-The insulator serves two purpose. They supportthe conductor (or bus bar) and confine the current to the
conductor. The most commonly used material for themanufactures of insulators is porcelain. There are several type ofinsulator (i.e. pine type, suspension type etc.) and there used in
Sub-Station will depend upon the service requirement.
3) Isolating Switches :-In Sub-Station, it is often desired todisconnect a part of the system for general maintenance and
repairs. This is accomplished by an isolating switch or isolator.An isolator is essentially a kniff Switch and is design to oftenopen a circuit under no load, in other words, isolator Switchesare operate only when the line is which they are connected carryonload. For example, consider that the isolator are connected onboth side of a cut breaker, if the isolators are to be opened, the
C.B. must be opened first.
4) Circuit breaker:-A circuit breaker is an equipment, whichcan open or close a circuit under normal as well as faultcondition. These circuit breaker breaks for a fault which can damageother instrument in the station. It is so designed that it can beoperated manually (or by remote control) under normalconditions and automatically under fault condition. There aremainly two types of circuit breakers used for any substations. Theyare (a) SF6 circuit breakers; (b) spring circuit breakers. For the latteroperation a relay wt. is used with a C.B. generally bulk oil C.B.are used for voltage upto 66 KV while for high voltage low oil &SF6 C.B. are used. For still higher voltage, air blast vacuum orSF6 cut breaker are used.The use of SF6 circuit breaker is mainly in the substationswhich are having high input kv input, say above 132kv and more. Thegas is put inside the circuit breaker by force ie under high pressure.When if the gas gets decreases there is a motor connected to thecircuit breaker. The motor starts operating if the gas went lower than20.8 bar. There is a meter connected to the breaker so that it canbemanually seen if the gas goes low. The circuit breaker uses the SF6gas to reduce the torque produce in it due to any fault in the line. The
circuit breaker has a direct link with the instruments in the station,when any fault occur alarm bell rings.