CIRCUIT BREAKER FAILURE AT POWER PLANT
When: Mid May 2011
Where: The Asheville Power Station (Unit 1) near Arden, NC
This is a two-unit coal-fired plant with a combined power output of 392 Mw.
The following is information is from the plant manager.
At approximately 3:00 pm, a circuit breaker in a 4,160-volt bus failed. The unit was offline and
all workers are safe.
I&Cs (Instrument & Control) personnel were testing the 1D Soot Blowing Air Compressor
(SBAC) motor as part of a fuel flexibility project. The motor was bumped two times for rotation.
The I&C supervisor observed the motor bumps at the circuit breaker and thought that he saw a
double start during the last bump. After a discussion with an I&C worker, they decided to use a
spare circuit breaker to troubleshoot.
The I&C worker donned an arc-flash suit and racked a spare circuit breaker into the cubicle in
the ON position. The I&C supervisor entered the load center after the worker had racked in the
circuit breaker.
The worker removed his arc-flash protection. The supervisor and the worker then decided that
the worker would go to the local switch at the air compressor and change the position from OFF
to REMOTE for testing. The supervisor remained behind to observe.
While the worker walked to the local switch, an explosion occurred in the 1D SBAC motor circuit
breaker cubicle (see figures 1 and 2).
A full investigation and root cause analysis is underway.
Figure 1 - Accident Scene
Figure 2 - Close up of the blown-off cubicle door with top facing back towards the enclosure.