Seattle City Light is trying to determine the cause of a fire Wednesday at a power substation near Seattle Center that left 325 customers without power, including the Monorail.

The fire started shortly after 10 a.m. inside a capacitor bank at Seattle City Light’s Broad Street Substation, at Sixth Avenue and Harrison Street, according to Seattle Fire Department spokesman Kyle Moore. The fire sent a thick plume of black smoke roiling through the air.

A capacitor bank uses mineral oil and is a sort of battery that helps electrical volts disperse evenly, said Moore and a spokesman for City Light.

Because the capacitor at the Broad Street substation had 26,000 volts of electricity running through it and the fire was contained, firefighters determined that the safest course of action was to let the fire burn out on its own, Moore said.

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There were no injuries reported, but 325 customers in the Seattle Center area lost power for a short time, City Light’s Peter Clarke said.

Seattle Center spokeswoman Deborah Daoust said lights flickered momentarily and a few people lost documents on their computers, but that was the worst of it.

She said Seattle Center has a backup power supply. The Space Needle and EMP Museum also have backup power sources, or generators.

The Monorail, Daoust said, was shut down, but was running again a few hours later.

Clarke said later Wednesday that the capacitor had not cooled down enough for investigators to determine the cause.

Seattle Times staff reporter Jennifer Sullivan contributed to this story.Christine Clarridge can be reached at or 206-464-8983.