Ground Fault Protection Applications in Low Voltage Motor Control Systems for Process Industries

Continuous processes require motor control systems to maintain uptime in a variety of installed system types. New capabilities in low-voltage (LV) motor protective relays have enabled ground fault protection to be specially tuned for these process needs. This paper will examine several design alternatives for engineers considering site ground fault protection needs in low voltage motor control systems for commonly applied power system types including ungrounded, solidly grounded and resistance grounded). The importance of application in motor life, fault detection, motor failure examples due to ground fault and electrical safety will be considered. Typical methods of ground fault protection in LV motor control centers and common challenges for ground protection schemes including residual, zero sequence and high resistance ground (HRG) pulse detection systems to achieve fast fault detection and ground fault protection for LV motor control centers (MCCs) will be addressed. Finally, a case study involving an industrial project technology review and installation of a HRG pulse detection system for a newly installed LV MCC will be reviewed.