SUBSTATION OVER VIEW

Presented byT . Sai Krishna14G25A0217Ascet-Gudur

Guide:Mr.G.Venkateswarlu,M.Tech.

A Station is a subsidiary station of an electricity generation, transmission,& distribution system where voltage is transformed to high to low or the reverse using transformers.

A substation generally have switching, protection, & control equipment & one or more transformers

Classification based on voltage levels, e.g. : A.C. Substation : EHV, HV, MV, LV; HVDC Substation.

Classification based on Outdoor or Indoor : Outdoor substation is under open sky. Indoor substation is inside a building.

Classification based on configuration, e.g. : Conventional air insulated outdoor substation orSF6 Gas Insulated Substation (GIS)Composite substations having combination of

the above two

Primary Substations receive power from EHV lines at 400KV, 220KV, 132KV and transform the voltage to 66KV, 33KV or 22KV (22KV is uncommon) to suit the local requirements in respect of both load and distance of ultimate consumers. These are also referred to ‘EHV’ Substations.

Secondary Substations receive power at 66/33KV which is stepped down usually to 11KV.

Distribution Substations receive power at 11KV, 6.6 KV and step down to a volt suitable for LV distribution purposes, normally at 415 volts

Outdoor Switchyard Incoming LinesOutgoing LinesBus barTransformersBus post insulator & string insulatorsSubstation Equipment such as Circuit-

beakers, Isolators, Earthing Switches, Surge Arresters, CTs, VTs, Neutral Grounding equipment.

Station Earthing system comprising ground mat, risers, auxiliary mat, earthing strips, earthing spikes & earth electrodes.

Overhead earth wire shielding against lightening strokes.

Galvanised steel structures for towers, gantries, equipment supports.

PLCC equipment including line trap, tuning unit, coupling capacitor, etc.

Power cablesControl cables for protection and controlRoads, Railway track, cable trenchesStation illumination system

Vented / Flooded Lead Acid batteries

Sealed maintenance free batteries/Valve Regulated Lead Acid

Nickel Cadmium (Ni-cd) batteries

VOLTAGE LEVEL MINIMUM GROUND CLEARANCE

less than 66kV 6.1m

66kV - 110kV 6.4m

110kV - 165kV 6.7m

greater than 165kV 7.0m

Major power station= 0.5 Ohm.

Major Sub-stations= 1.0 OhmMinor Sub-station = 2 OhmNeutral Bushing. =2 OhmService connection = 4 OhmMedium Voltage Network =2

OhmL.T.Lightening Arrestor= 4

OhmL.T.Pole= 5 OhmH.T.Pole =10 OhmTower =20-30 Ohm

Type Voltage

EXTRA LOW VOLTAGE

Up to 50V AC/DC

LOW VOLTAGE 50-1000V AC/DC

MEDIUM VOLTAGE ABOVE 1000V AC/DC UPTO 6.6KV AC

HIGH VOLTAGE ABOVE 6.6KV AC TO 33 KV AC

EXTRA HIGH VOLTAGE

ABOVE 33KV AC TO 400 KV AC

ULTRA HIGH VOLTAGE

ABOVE 400 KV AC TO 765 KV AC

The following steps, when put into practice, will ensure a reliable, safe and trouble-free substation grounding system:

Size conductors for anticipated faultsUse the right connectionsGround rod selectionSoil preparationGrounding using building foundations Grounding the substation fence Special attention to operating points Surge arrestors must be grounded properly Grounding of cable trays Temporary grounding of normally energized parts 

Laying direct in ground In pipes, Closed or Open ducts, Cable trays and On surface of wall

Fire fighting systemD.G. SetOil purification system