Unit 2 at Diablo Canyon nuclear power plant returned to full power Tuesday after the unit unexpectedly shut down July 10 when an electrical disturbance occurred in equipment that supports moving power to the states electric grid.
An investigation into the shutdown determined the electrical disturbance was a result of a flashover event on a lightning arrestor located on the non-nuclear side of the plant, Pacific Gas and Electric Co. said in a news release.
The flashover occurred during routine maintenance that involved pressure washing, known as hot washing, of electrical insulators near the lightning arrestor. Upon sensing the disturbance, the unit performed as designed and automatically went off line to protect equipment. Unit 1 was unaffected and continued to generate power.
Following the successful repair of the lightning arrestor, Unit 2 began providing electricity to the state's power grid on July 14, and safely transitioned to 100 percent power Tuesday morning.