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SUBSTATION OVERVIEW
-B. Prasad
Chartered Engineer
[e-mail]

TYPE OF SUBSTATION
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 or
SF6 Gas Insulated Substation (GIS)
Composite substations having combination of the
above two

Classification based on application
Step Up Substation : Associated with generating station as
the generating voltage is low.
Primary Grid Substation : Created at suitable load centre
along Primary transmission lines.
Secondary Substation : Along Secondary Transmission Line.
Distribution Substation : Created where the transmission line
voltage is Step Down to supply voltage.
Bulk supply and industrial substation : Similar to distribution
sub-station but created separately for each consumer.
Mining Substation precaution for safety needed in the
operation of electric supply.
Mobile Substation: Temporary requirement

PROMARY/SECONDARY/DISTRIBUTION
SUBSTATION
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

SUBSTATION PARTS AND EQUIPMENTS
Outdoor Switchyard
Incoming Lines
Outgoing Lines
Bus bar
Transformers
Bus post insulator & string insulators
Substation Equipment such as Circuit-
beakers, Isolators, Earthing Switches, Surge
Arresters, CTs, VTs, Neutral Grounding
equipment.