13.8-kV Selective High-Resistance Grounding System for a Geothermal Generating Plant—A Case Study

The 13.8-kV selective high-resistance grounding (HRG) systems for bus-connected generators are nonexistent due to two reasons: One is that the stray capacitance current of the system can be high (> 10-12 A), and the other is that the sensitivity and selectivity of the ground-fault devices to detect low levels of ground-fault currents are required. This paper describes the relay types, sensors, settings on protective relays, and flow of currents for various fault locations in a 13.8-kV system and demonstrates how a selective HRG has been implemented. To the authors´ knowledge, there is no HRG selective system at 13.8 kV.