‘Mistake’ caused downtown Seattle’s massive power outage

Officials with Seattle City Light have announced the cause of the massive power outage that plagued downtown Seattle last week.

After reviewing what happened, Seattle City Light CEO and General Manger Larry Weis said the outage was caused by “mistake” when engineers “overlooked” a potential problem while testing new equipment at the Massachusetts Substation.

“It is an operations mistake,” Weis said. “We apologize for it. It is a unique situation to how City Light’s system is set up.

“It was a unique situation that the engineers who set up the protocol overlooked,” he added.

In short, new equipment was being tested at the Massachusetts station. Engineers took the primary breakers that could be affected during the tests into account but overlooked the backup breakers. When those breakers were affected during testing, it knocked out power to the station as well as the Union Street Substation.

“This cut power coming from two high-voltage transmission lines providing power to the Union Substation,” Weis said.

“Everything operated as it was supposed to do,” he said. “In the process in setting this up, they did overlook this relay scheme in the system.”

The power outage put 60 percent of downtown Seattle in the dark on the morning of Wednesday, May 25. It caused traffic disruptions when traffic lights went out, darkened homes and offices and trapped people in elevators.

No City Light personnel will be fired or disciplined over the incident, Weis said. Seattle City Light is reviewing its testing procedures in the wake of the outage.

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