It doesn’t happen all that often, but when it does, it’s not pretty.
Edvard at the Electric Engineering Portal gives us the breakdown of substation fires:
There are a wide range of types and causes of the fires that can occur in substations. The types of fires depend on the equipment and systems used in the stations. Fires involving dc valves, outdoor or indoor oil-insulated equipment, oil-insulated cable, hydrogen-cooled synchronous condensers, or PCB-insulated equipment are usually well documented, and these types of equipment are easily recognized as a fire hazard. There are a number of other substation-specific types of fires that are not as well documented.
Edvard, as usual, provides an excellent synopsis of the hazards that befit an electrical substation. Please read the whole thing.