GRAND COULEE — A jolt from electrically charged water knocked some of the concrete facing off Grand Coulee Dam’s left powerhouse.
No one was injured in the Oct. 23 incident, which didn’t damage powerlines, generators or transformers, according to the U.S. Bureau of Reclamation.
A fault occurred when the Generator 8 penstock was being refilled with water to return the unit to service after maintenance.
A penstock is a pipe that carries water to the unit. As it refilled, air and water were forced out of a vent valve on the face of the dam.
The water hit a nearby energized powerline, causing electricity to inadvertently flow from the line to the vent valve. The resulting jolt of electricity blew a small amount of concrete facing off the dam.
The bureau is performing an analysis to prevent similar events in the future.
The left powerhouse is one of four that house the dam’s 33 generators.
In June, a fire and explosion damaged the right powerhouse. The problem happened when a circuit breaker failed to trip after an electrical fault. No one was injured, but one of the generators was off line for repairs for several weeks.