For cost and safety, the outdoor substations are installed for voltages above
Right Answer is:
Indoor substation: Generally, this substation is used for voltage up to 11 kV. However, when the atmosphere is polluted with impurities, this substation is also erected up to 33 kV. All items of the equipment are installed indoors for economic reasons. The indoor substation consists of either an enclosed or open compartments or chambers in which the main equipment of the substation is installed.
Outdoor substation: It is used for voltages above 33 kV. Due to high voltages, the clearance between conductors and the space required for switches, circuit breakers, and other types of equipment is very large and the indoor substations are not suitable economically.