This was in the SWJ News round up today, but based on the video link it appears this attack took place in April. Based on the description of the attack it was not simple vandalism. It was likely conducted by an insider with a grudge, or an individual/group that received some professional level sabotage training. I'm surprised there not was more damage, but since there were no reported follow on attacks I'm guessing this was a grudge attack.

http://complex.foreignpolicy.com/pos...litary-assault

"Military-Style" Raid on California Power Station Spooks U.S.

"These were not amateurs taking potshots," Mark Johnson, a former vice president for transmission operations at PG&E, said last month at a conference on grid security held in Philadelphia. "My personal view is that this was a dress rehearsal" for future attacks.
He isn't correct about .22, but his point is still valid, and apparently he doesn't work for the government because he actually has a common sense recommendation.

A shooter "could get 200 yards away with a .22 rifle and take the whole thing out," Wellinghoff said last month at a conference sponsored by Bloomberg. His proposed defense: A metal sheet that would block the transformer from view. "If you can't see through the fence, you can't figure out where to shoot anymore," Wellinghoff said. Price tag? A "couple hundred bucks." A lot cheaper than the billions the administration has spent in the past four years beefing up cyber security of critical infrastructure in the United States and on government computer networks.