scope:

Description of Driving Event:

A 500 HP service air compressor stayed engaged after a stop command was issued from the central control dispatcher after a test run. The motor came to an abrupt halt and started to burn, causing extensive damage. The primary damage occurred to the compressor motor as the coils were burned. Damage also occurred to the starter in the form of blown fuses and burned contacts.

The cause of the mishap was a direct result of an inadvertently bent follower arm on the starter. When the central control dispatcher commanded the control circuitry off, the DC field was turned off but the starter stayed engaged. The angle of the bent follower arm allowed it to fall behind the walking beam assembly preventing the starter from disengaging. The running of the motor out of synchronism without field exitation caused overheating of the cage windings to the point where the motor started to burn.