Well, hypothetically for theoretical, academic discussion if you're engaging in an fictitious insurgency;
It depends on the base, some have their own generating facilities…while others rely on the commercial external grid. All bases have ancillary means of power, such as generators/solar arrays, ect…and this is the military we're talking about here, operating without a stable and readily available power source is apart of their capabilities.
Extensive and robust. Non-nuke generating facilities are generally contract security trained to DoE standards…Nuke generating facilities are guard by DoE-NNSA personnel…all personnel regardless of facility are armed, trained, and have lethal RoE.
In industrial areas, of course at night, using something like high tensile steel cable thrown across lines of larger transformers, causing arc and burnout. Use a tool like a modified pole pike, peavey, hookaroon, or pick to puncture the oil and coolant drums of the transformers, and leave behind anti-vehicular devices such as caltrops or spike strips to disable any responding vehicles, be it local administrative enforcement or repair personnel. Silence is the key.
You can't and won't. Modern railroad utilizes CBTC/CTC (Communication-Based Train Control/Centralized Traffic Control) both utilize a frequency over the rail line to transmit data. Every segment of rail is electrified with a low-volt system, the moment a section of track was damaged they'd know. Also, any stretch of rail that is going to have an impact if damaged/removed will also be heavily traveled, with a train passing every hour to every half-hour…nowhere enough time to preform any kind of covert track sabotage. Also, during contingency operations sections of track become US Government property strictly for government/military use as outlined in STRACNET.
Where and how deep are underground lines/pipes place for supplying water and electrical energy to the enemy?
Water is not generally piped any great distance, it's normally drawn from a reservoir or tower into a treatment plant at a nearby urban area, it's piping is also heavily decentralized after it leaves the treatment plant…much of it redundant to serve as ancillary aqueducts in the event of a pipe burst or sheer.
You can't and won't. It would require an extremely large amount of explosives to do any significant damage to a tower. It would also require to be detonated using an analog remote detonator because the lines themselves would interfere with any wireless remote detonator. Tackling substations, switching stations, and transformers is far easier, requires less resources, can be done covertly, and all by an individual.