Did You Really Test That Interlock?

A chemical manufacturing facility installed a new substation to provide a second electrical source to 480 V equipment that was critical to site operations, such as steam boilers. The new substation used 27 kV gas insulated switchgear to help reduce the size of the new substation. During checkout of the gas insulated switchgear, a SF6 low-pressure switch circuit was found to not function properly. Both the low-pressure alarm and the circuit breaker trip due to low-low-pressure did not work. Troubleshooting of the problem identified the control circuit wiring from the switchgear manufacturer was not correct so the circuit could not operate properly. Field commissioning by the switchgear manufacturer did not identify the miswiring. This paper discusses how this defect went unidentified and provides some suggested steps to help prevent this issue.