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Primary substation is generally
Indoor type
Outdoor type
Pole mounted type
Any of above
Outdoor type
Primary substations are large-scale installations that receive power from high-voltage transmission lines and step it down for regional distribution. Due to the high voltage levels (typically 66kV, 132kV, or higher) and the massive physical size of transformers, circuit breakers, and isolators, these are almost exclusively built as outdoor installations to ensure safety clearances and heat dissipation.
Primary substations are large-scale installations that receive power from high-voltage transmission lines and step it down for regional distribution. Due to the high voltage levels (typically 66kV, 132kV, or higher) and the massive physical size of transformers, circuit breakers, and isolators, these are almost exclusively built as outdoor installations to ensure safety clearances and heat dissipation.
VsтАЛ=VpтАЛ├ЧNpтАЛNsтАЛтАЛ тАФ Transformer transformation ratio for voltage step-down
P=3тАЛVLтАЛILтАЛcos╧Х тАФ Total power rating calculation for substation sizing
The principle relies on the insulation requirements of high-voltage equipment. Air serves as the primary insulating medium for the high-voltage busbars and conductors in outdoor substations, which is cost-effective and provides natural cooling for high-power transformers. In contrast, indoor substations are reserved for medium-to-high voltage urban applications (e.g., 11kV/33kV) where space is limited and environmental conditions must be controlled.
Primary substations handle transmission voltages (66kV-400kV).
Outdoor design allows for natural air cooling of large power transformers.
Significant electrical clearances are required to prevent flashover at high voltages.
Outdoor substations are more economical to build due to lack of enclosed building requirements.
Lower initial capital expenditure.
Easier maintenance access for large heavy-duty equipment.
Natural ventilation and cooling for high-power components.
Vulnerability to atmospheric conditions (lightning, humidity, pollution).
Requires significantly larger land area.
Higher risk of bird/animal-related outages.
Connecting transmission grid to regional distribution network.
Power stepping for heavy industrial complexes.
Interconnection points for national grid networks.
Indoor substations are usually Gas Insulated Substations (GIS) used in highly populated or polluted urban areas.
Pole-mounted substations are strictly for low-capacity distribution (typically up to 11kV/415V).
B is correct тАФ Primary substations utilize outdoor switchyards due to the massive clearance requirements of high-voltage transmission equipment.
Always remember: higher voltage level implies larger air clearance, directly correlating to a preference for outdoor substation layouts.