CenterPoint Energy 12 kV network feeder ‘back feed’ protective relaying

In 2006 CenterPoint Energy experienced a substation 12 kV switchgear circuit breaker failure/fault. The substation protective relaying isolated the failed/faulted circuit breaker. However the 12 kV switchgear circuit breaker that failed was connected to a feeder that supplied a 480 V spot network system. The network protectors did not all operate in a timely manner and the resultant feeder `back feed´ into the substation 12 kV switchgear circuit breaker fault caused significant damage to the switchgear and 12 kV bus inside of the switchgear building. This paper reviews the sequence of events and resulting damage, investigation into the cause of the events, corrective actions including the implementation of a new substation based `back feed´ protective relaying scheme. This paper also reviews a 2012 fault in the 12 kV switchgear and performance of the new substation based `back feed´ protective relaying scheme. The paper concludes with a discussion of the background and equipment design, including protective relaying, of a project that is present under construction to replace the substation 12 kV conventional switchgear with GIS switchgear.