Overcurrent protection device miscoordination issues that result in plant outages and costly down time

This paper discusses the phase and ground overcurrent protection of chemical facility electrical supply systems with emphasis on situations that can result in unnecessary shutdown of services. Ground overcurrent relay coordination with downstream fusing, the coordination of successive levels of protection with instantaneous devices, coordination of low voltage secondary devices with primary devices through delta-wye connected transformers, and coordinating successive levels of low voltage devices are emphasized. Examples show situations where electrical faults can result in unintended shutdown of services, and include solutions applied to result in a more selective overcurrent protection system.