| SR. NO | PARTICULAR | OUTDOOR SUBSTATION | INDOOR SUBSTATION |
| 1 | Space Required | More | Less |
| 2 | Time Required For Erection | Less | More |
| 3 | Future Extension | Easy | Difficult |
| 4 | Fault Location | Easier Because The Equipment Is In The Full View | Difficult Because The Equipment Is Enclosed |
| 5 | Capital Cost | Low | High |
| 6 | Operation | Difficult | Easier |
| 7 | Possibility Of Fault Escalation | Less Because Greater Clearances Can Be Provided | More |
| 8 | Figure |  |
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From the above comparison, it is clear that each type has its own advantages and disadvantages.
However, comparative economics (i.e. annual cost of operation) is the most powerful factor influencing the choice between indoor and outdoor sub-stations. The greater cost of indoor sub-station prohibits its use. But sometimes non-economic factors (e.g. public safety) exert considerable influence in choosing indoor sub-station. In general, most of the sub-stations are of outdoor type and the indoor sub-stations are erected only where outdoor construction is impracticable or prohibited by the local laws.
Reference:
“Power system” by V.K. Mehta