This “operation” sounds like a book on my Kindle - “Gridlock”. A terrorist/assassin used a rifle to take out some insulators as a small substation in North Dakota. This was the first attack to take out the entire grid. He wanted to make this first attack serious, so he waited until a lineman came to climb up and do his work, then he shot and killed him. Then, bad guy went away.
It appears some think this California Power Station is a dress rehearsal for “much larger assault on US grid.” Well, that is the way it started in this book.
That would be an extreme psychological multiplier in such a prolonged attack. If the repair crews could not be freely dispatched to damaged locations for fear of snipers waiting for them when they arrive, then it would grind repair work to a halt. A simple cut pole in the middle of a field would turn into a potential kill zone for a utility crew that came to fix it. The attackers would own the night.