BC Hydro 15 kV cable explosion

This investigation was prompted by a cable fault explosion inside a cable duct which housed a BC Hydro 15 kV underground standby feeder cable. The incident occurred in September 1998 at a housing complex in Vancouver, BC, Canada. Damage to the building vault was extensive and could very easily have resulted in severe injury or a fatality had anyone been in the immediate area of the vault. A failure analysis investigation revealed that the cause of the explosion was an accumulation of combustible gases which were decomposition products of the polymeric cable components which were liberated from the cable by a long duration high impedance fault. Several unusual circumstances had to occur concurrently to allow the explosive condition to develop. The events that led to the explosion are discussed in terms of the failure mechanism of the cable and the effects of reclosure arcing.