Transformers do not automatically switch on. They are always energized unless there is an internal fault on the transformer and then a crew will come open some air switches to isolate it from the system and then it can be investigated. There are a thing called autotransformers but that’s referring to the transformer changing taps and adjusting its voltage according to support the load at any given time. Every air switch in the sub must be operated by a person. Nothing switches in or off automatically except for the opening of the breakers under a fault condition. All breakers can be remotely controlled via SCADA but that’s another topic. Substation maintenance includes: doing maintenance on the breaker itself...testing the condition of the insulating medium of the breaker (oil, gas, etc), checking the contact wear of the breaker, measuring resistance across the closed contacts of each phase, doing power factor tests on all the PTs, doing the same tests on capacitor banks and regulators if the sub has them, there may be more but it’s 4 am where I am right now. That’s for planned maintenance. If any condition arises which is noticed by SCADA then a crew will come out and do perform a megger or TTR test and replace whatever needs to be replaced. That’s the basic jist of maintenance, each utility may be different but they all do circuit breaker maintenance. There are different bus configurations that allow any one circuit breaker to be de-energized for maintenance/repairs/replacement or whatever without losing the load for the line that breaker is tied into. Double breaker double bus, breaker and a half, aux bus, ring bus, etc. you can look up these terms to see more about them if you want. The load can be switched through various different subs and switch yards in emergency or planned outages if need be like in a big storm or whatever. The system operator who sits in an office and has a view of the overall system and control of the whole system can see how everything is tied together and if a line goes out in an emergency can still find a way to supply load to the customer via a different substation. The system operator has remote control of every breaker via SCADA (supervisory control and data acquisition, basically remote control over everything, and can see the power flowing through each sub, different alarms associated with each sub, etc). In my utility we build the subs and do upgrades which is my favorite part..:replacing breakers, PTs, regulators, hanging bus, etc basically anything that needs to be replaced. Or just building an entire sub from the ground up. Each utility may be different in that aspect. I hope I answered some of your questions let me know if I missed anything