It seems like an awful lot of trouble to take a substation down.
Must be really difficult to hurt the equipment.
I would say it was more of a real world test to see what equipment the ammo could penetrate/break, and how the equipment would react. How fast the oil drains out and the like. Like a cat playing with a mouse to hone its ability to attack.
Taking into account the likely persuasion of the people doing it I would say they probably used AK47s with steel core AP ammo. Or they may have even used a variety of ammo to see which was most effective.
And the other thing I would say they are keeping an eye on is how long it took the company to affect the repairs. Like how much work the company had to do to repair equipment, and how long, or if they had to replace it outright depending on the damage.
I would also speculate that they intentionally damaged some equipment more than other equipment, or in different ways to see how much damage they had to do to make the repairs take as long as possible, or make repairs impossible.