PG&E Corp. says it will build opaque fences around critical transmission substations, including at the Metcalf substation that was heavily damaged by gunmen firing from outside a chain-link fence last year. The San Francisco-based utility, which serves Northern California, is also staffing important locations overnight. The company had eliminated some nighttime shifts after it built a power-system control center in Vacaville, Calif., in 2009. PG&E and other utilities announced new safety measures after The Wall Street Journal reported last week that the attack on the Metcalf transmission substation raised concerns about the vulnerability of the electric grid to physical sabotage. Jon Wellinghoff, the former chairman of the Federal Energy Regulatory Commission, called the incident an act of terrorism. The attack on the Metcalf substation, south of San Jose, Calif., began after 1 a.m. April 16 by gunmen who took out 17 of the 20 giant transformers that funnel power […]