Considerations for ground fault protection in medium-voltage industrial and cogeneration systems

Several aspects are presented of system grounding and the limitations of some systems with respect to applying ground fault protection to industrial distribution networks. Relays cannot prevent damage by themselves, nor can they be applied to compensate for design deficiencies. It is pointed out that there is no one absolute solution to system grounding and/or protection, but judgment can be exercised by considering some of the major phenomena described herein. The typical methods for grounding of medium-voltage neutral systems (high resistance, low resistance, and ungrounded) as well as methods used to detect the presence of ground faults are reviewed. Also, the effects of charging current and how the ground fault protection method could affect conductor railings are analyzed