sub stations-air insulated substations

SUB-STATIONS

INTRODUCTION

The assembly of apparatus used to change some characteristic(e.g. Voltage, a.c to d.c, frequency, power factor etc) of electric supply is called a sub-station

SITE SELECTION …..

• It should be located at the centre of gravity of load

• It should be easily operated and maintained

• It should provide safe and reliable arrangement

• It should involve minimum capital cost

CLASSIFICATION OF SUB-STATIONS

Sub-stations

Service requirement

Constructionalfeatures

ACCORDING TO SERVICE REQUIREMENT

Transformer sub stations : these are used to change the voltage levels of supply

switching sub stations: they simply perfome switching operations of power lines

Power factor sub stations: they improve the power factor of the system by using synchronous condensers

Frequency sub stations: those sub stations which change supply frequency

Converting sub stations: those sub stations which change a.c. power to d.c. power

Industrial sub stations: those sub stations which supply power to industries

Substations are classified as……..

TRANSFORMER SUB-STATIONSTransformer substations are classified into 4 types these are……..

step up substation: the generation voltage is stepped up to high voltage

Primary grid substation: here the voltage level is step down to 66kv from 220kv for secondary transmission

Secondary substation: the voltage level is further step down to 11kv and these substations are generally outdoor type

Distribution substation: the electric power from 11kv lines is delivered to distribution substation. These are generally located near consumer localities…

ACCORDING TO CONSTRUCTIONAL FEATURES

According to constructional features, the sub stations are classified as:

Indoor sub station: these substations can be installed for voltages up to 11kv

Outdoor sub station: for voltages beyond 66kv these type of sub stations can be installed

Underground sub stations: in thickly populated areas, the space available is less so we install these type of substations

Pole mounted substations: this is an outdoor substation with equipment installed overhead on h-pole or 4 pole structure

INDOOR SUBSTATION…..

BLOCK DIAGRAM>>>>>>

pole mounted substationIt is a schematic view of pole mounted substation……

POLE MOUNTED SUBSTATION……

UNDERGROUND SUBSTATION……While designing a underground sub station the following points are to be followed:

the size of substation should be minimum

There should be reasonable access for both equipment

There should be provision for emergency lights and protection against fire

There should be good ventilation

the transformers,switches,fuses should be air cooled to avoid bringing oil into premises

Schematic view………

SYMBOLS FOR EQUIPMENT IN SUB STATIONS

EQUIPMENT IN A TRANSFORMER SUB STATION

BUS BARS: various incoming and out going circuits are connected to bus bars.busbars receive power from incoming circuits and deliver power to out going circuits.

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Electric substations are the part of power systems and used for transferring power from generating points to load centres.some of important components are…

INSULATORS: insulators serve two purposes 1) they support conductors(busbars) 2) confine the current to the conductors most commonly used material for manufacture of insulators is porcelain.

ISOLATING SWITCHES: in sub stations it is often desired to disconnect a part of system for general maintenance and repairs. this is accomplished by an isolating switch or isolators.

Circuit breaker: circuit breaker is used for switching during normal and abnormal conditions. it is used to interrupt short circuit currents .there are many types of circuit breakers.. 1) air blast circuit breaker. 2) oil circuit breaker 3) sf6 circuit breaker

power transformers: these are used to step down or step up a.c. voltages and to transfer electrical power from one voltage level to another.

Current transformers: current transformer in essentially a step up transformer which steps down the current to a known ratio.

voltage transformer: it is essentially a step down transformer and steps down the voltage to a known ratio.

metering and indicating instruments: there are several metering and indicating instruments installed in a sub station to maintain watch over the circuit quantities.

in addition to these there may be following equipment in a substation. 1) fuses 2) carrier current equipment 3) sub station auxiliary supplies

BUS BAR ARRANGEMENTS IN A SUBSTATION

Single bus bar system…

Duplicate bus bar system…..

Key diagram of 66/11kv substation

Key diagram of 11/440v indoor substation

GAS INSULATED SUBSTATION

INTRODUCTION…

Gas Insulated substations use sulphur hexa fluoride(SF6) gas which has superior dielectric properties. Gas insulated substations are used where there is space for providing the substation is expensive in large cities and towns

TYPES OF GAS INSULATED SUBSTATIONSGas insulated substations are classified according

to the type of configurations as………..

isolated phase module

3-phase common modules

hybrid modules

Compact modules

Highly integrated systems

Isolated-phase module

The individual circuit elements such as a pole of a circuit breaker, a single pole isolator, one phase assembly of a current transformer etc..are connected together forms an isolated phase GIS module.

THREE PHASE COMMON MODULE

In this type of module a three phase bay is assembled using the desired number of three phase elements. This reduces the total number of enclosures to one third.

HYBRID MODULES

It is the combination of isolated phase and three phase common elements is used to achieve an optimal solution. Hybrid GIS technology has gained popularity, specially in the medium and low voltage range

COMPACT MODULE

Compact GIS systems are essentially three phase common systems in which the elements such as three phase circuit breaker, current transformer etc…. Are placed

HIGHLY INTEGRATED SYSTEM

These are used in outdoor substations .highly integrated substations are ready to install substations.

SINGLE LINE DIAGRAM

BUS BARS

The high voltage conductor made up of copper or aluminum is centrally placed in a tabular metal enclosure. In isolated phase GIS ,coaxial bus bar are common

Constructional aspects of GIS……..

The main parts of GIS are…….

gas circuit seals and gaskets disconnectors earth switchCircuit breakerCurrent transformerPlug in jointsEnclosureExpansion joints

Gas circuit : gas circuit has to maintain the dual purpose (i.e. arc interruption and insulation). Gas circuit should maintain the pressure throughout its life period so there should be no leakages

SEALS AND GASKETS : seals and gaskets are used to capture the SF6 gas lekages.these are manufactured with nitrile rubber and viton. These serves sealing purpose

Disconnectors…..Disconnectors or isolators are used for electrical isolation of circuit parts.They are slow acting and operating at off load.Disconnectors must be carefully designed and tested to be able to break small charging current without generating too higher over voltage.

Circuit Breakers…….

Circuit breaker is a metal clad and uses SF6 gas for the purpose of insulation and fault interruption. The circuit breaker is directly connected to either current transformers or isolators

Earthing switch……

fast earth switch: these are used to protect the circuit connected current transformer, voltage transformer

Maintenance earth switch: these are used for grounding the high voltage conductors during maintenance

PLUG IN JOINTS: these are designed in such a way that they can carry rated full load current uninterruptedly and can carry heavy transient currents types of plug in joints areStatic jointsQuasi static joints

MAINTENANCE AND INSTALLATION

S.NO 145KV 170KV 245KV

1 Bay width (m)

1.5 2.0 2.0

2 Bay depth 3.3 3.35 3.4

3 Bay height 3.2 3.4 3.4

4 Floor area(sq.m)

4.95 6.7 6.8

5 Volume 15.84 22.78 23.12

6 Weight 3800 5000 5700

Advantages of GIS….

GIS have no risk for fire and explosion due to leakage of oil.They generate no noise and have no radio interference.The maintainence of GIS is free.It offers solutions, -Industrial areas where space and pollution problems . -Mountain areas where ice and snow are major problems.

Disadvantages of GIS…….

Gas insulations tend to be much more expensive than air insulated installations with the same ratings.Care should be taken that no dust particles enter into the live compartments which results in flash over.When fault occurs internally the diagnosis of the fault and rectifying takes very long time.

COMPARISON OF AIR INSULATED SUBSTATIONS AND GAS INSULATED SUBSTATIONS

THANK YOU..