Switch Problem Causes Outage

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Category: News

Created on Wednesday, 04 February 2015 15:37

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By Sentinel Staff

Sitka lost power for about 40 minutes this afternoon while the electric department was switching back to Blue Lake hydrogenerators after a maintenance project, Department Director Chris Brewton said.

“When we went to return normal service, and switch back to Blue Lake hydros, the diesel circuit breaker tripped,” he said. 

Electrical service to the whole town was out between 1:40 until 2:20 p.m.

Brewton explained that during the maintenance project the power was switched to one Green Lake turbine – providing 9 megawatts – and the city’s diesel turbine – providing 12 megawatts. The demand at the time was about 17 megawatts.

During the project, workers isolated a transformer in the Blue Lake substation in order to safely work on the de-energized equipment. When work was completed, workers closed the breaker to re-energize the transformer, Brewton said.

“That event appeared to cause the diesel generator turbine breaker to open,” Brewton said. “With the loss of 12 megawatts, that put our system into an under-frequency condition, and our distribution under-frequency protection opened the feeders.” Which means, he said, the power went out.

There was no apparent damage caused by the outage, and department workers are continuing to assess why the breaker opened during the switchover, Brewton said.

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