Best Practices for Implementing High-Resistance Grounding in Mine Power Systems

The proper implementation of high-resistance grounding of mine power systems reduces personnel hazards by limiting ground fault current and permits selective detection and clearing of faults. As described in IEEE Std. 142, high-resistance grounding employs a neutral resistor of high ohmic value, with the value of the resistor selected to limit the neutral ground resistor current to a magnitude equal to, or slightly greater than, the total capacitance charging current. Research has shown that the zero-sequence resistance of high-voltage mine distribution systems can be considerably larger than the magnitude of the system capacitive reactance, thereby violating the definition of high-resistance grounding. This paper outlines procedures for the proper sizing of the neutral grounding resistor (NGR) considering system capacitance. This paper begins with a discussion of problems associated with distributed capacitance in high-voltage high-resistance-grounded mine power systems. Subsequently, procedures for determining system capacitance, sizing the NGR, and establishing relay pickup settings are given. These procedures are straightforward to apply and require no computer modeling for implementation. Numerical examples applied to a high-voltage longwall utilization system and an underground mine distribution system are provided.