Low-resistance grounding method for medium voltage power systems

The authors present the basics of ungrounded system and system charging current and review medium-voltage system neutral grounding. Parameters affecting the rating of neutral resistors for low-resistance grounding method are discussed as well as limitations of low-resistance grounding methods. An analysis is made of how system charging capacitance affects the choice of grounding method. It is concluded that a relatively higher magnitude of system charging current would require either low-resistance grounding or high-resistance grounding with trip rather than alarm. At medium voltage either a low-resistance or a high-resistance grounding method can be used, depending on the system configuration, the presence of directly connected motors/generators, and plant process needs.<>