11-TRANSMISSION-SUBSTATION.pdf

7/24/2019 11-TRANSMISSION-SUBSTATION.pdf

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Sub-station

The assembly of apparatus used to change

some characteristic ( e.g. voltage , ac to dc,

frequency, pf, etc) of electric supply.

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Sub-station

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Laying out a substation

1. It should be located at a proper site. As muchas possible, it should be located at the loadcenter.

2. It should provide safe and reliablearrangement. For safety, consideration mustbe given to the maintenance of regulationclearances, facilities for carrying out repairsand maintenance, abnormal occurrencessuch as possibility of explosion etc.

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3. It should be easily operated and

maintained.

4. It should have a low initial cost

and low operational and

maintenance costs.

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Laying out a substation


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Classification of Sub-station

According to service

equipment According to constructional

features

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According to service equipment - called to asubstation to change voltage level or improvepower factor or convert ac to dc power

1. Transformer sub-stations2. Switching sub-station

3. Power factor correction sub-station

4. Frequency changer sub-stations

5. Converting sub-stations

6. Industrial sub-stations

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Transformer sub-stations

Change the

voltage level

of electricsupply

Transformers

are the maincomponent

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Switching sub-stations

Voltages are

not changed

Simply

performs the

switching

operations of

power lines

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Power factor correction

sub-stations Improve the power factor

of the system

Generally located at thereceiving end of the lines

Generally usessynchronous condensers

as the power factorimprovement equipment

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Frequency changer

sub-stations Change the

supply

frequency

Uses VFTs or

VFDs

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Industrial sub-stations

Specialized substations supplying to specific

industrial requirements

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According to constructional features

1. Indoor sub-stations

2. Outdoor sub-stations

3. Underground sub-station

4. Pole-mounted sub-station

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Indoor sub-stations

For voltages of

66kV

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Outdoor sub-stations

For voltages beyond66kV

For high voltages, the

clearances betweenconductors and thespace required forequipment becomeslarge that it is noteconomical to install

the equipmentindoor.

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Underground sub-stations

Used for:

highly populated

areas when space available

for equipment andbuilding is limited

when cost of land ishigh.

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Underground sub-stations

While laying out an underground sub-station, thefollowing points must be kept in view:

1. The size of the station should be as minimum aspossible.

2. There should be reasonable access for both equipmentand personnel.

3. There should be a provision for emergency lighting andprotection against fire.

4. There should be good ventilation.

5. There should be provision for remote indication ofexcessive rise in temperature.

6. The transformers, switches, and fuses should be aircooled to avoid bringing oil into the premises.

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Pole-mounted sub-stations

This is an outdoorsubstation withequipment installed

overhead on H-poleor 4-pole structure.

The cheapest formof sub-stations forvoltages not

exceeding 11kV ( or33 kV in somecases)

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The following points may be notedabout pole mounted sub-stations:

1. There should be periodical check up ofthe dielectric strength of oil in thetransformer and oil circuit breakers.

2. In case of repair of transformer or oil

circuit breakers, gang isolator should beopen and the circuit breaker should beisolated.

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Pole-mounted sub-stations


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Transformer sub-stations

Classifications

1. Step-up sub-station

2. Primary grid sub-station

3. Secondary sub-station

4. Distribution sub-station

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Step-up sub-stations

The generation voltage (13.8 kV to 24 kV) is

stepped up to high voltage (115 to 500 kV).

Outdoor type

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Primary grid sub-stations

Here, electric power is received by the

primary grid sub-station which reduces the

voltage level to 66kV to 115kV for secondary

transmission.

Generally of outdoor type

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Secondary sub-stations

Here, the voltage is further stepped

down to 4.16kV to 34.5kV. The lines

run along the important road sides ofthe city.

Generally of out-door type

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Distribution sub-stations

The electric power from 4.16kV to34.5kV lines is delivered to distributionsub-stations.

Located near the consumers localitiesand step down the voltage to 230V, 3-phase, 4-wire for supplying to theconsumers.

Majority of distribution sub-stations arepole-mounted type

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Equipment in a Transformer sub-station

1. Bus-bars

2. Insulators

3. Isolating switch

4. Circuit breaker5. Power transformers

6. Instrument transformers

7. Metering and indicating instruments

8. Others

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Documents

11-TRANSMISSION-SUBSTATION.pdf