The February 4, 2014 article by Rebecca Smith "Assault on California Power Station Raises Alarm on Potential for Terrorism (April Sniper Attack Knocked Out Substation, Raises Concern for Country's Power Grid)" fromThe Wall Street Journal further discusses the April 16, 2013 attack on a California energy substation. The article is unfortunately behind the WSJ paywall. However, a February 5, 2014 article titled "Attack on a California Transformer Could Have Been Dress Rehearsal for Terror Attack on Power Grid" at The Washington Free Beacon had a summary.
They quote Jon Wllinghoff, former FERC chair saying it was “the most significant incident of domestic terrorism involving the grid that has ever occurred (in the U.S.)” Another interesting quote: “This wasn’t an incident where Billy-Bob and Joe decided, after a few brewskis, to come in and shoot up a substation,” Mark Johnson, retired vice president of transmission for PG&E, told the utility security conference, according to a video of his presentation. “This was an event that was well thought out, well planned and they targeted certain components.”
It will be interesting to continue to track this and other events.
UPDATE 6 Feb 4:30pm EST - Here's the link to the WSJ Video (3:15 length).