Analysis of Ground Distance Protection Response on a Non-Bolted Fault at National Grid
The phase to ground fault is the most common fault type on transmission lines. The protection system shall work properly to identify and isolate faults quickly and minimize the impact on interrupting service to customers. Correct and rapid fault clearance and power outage minimization are of concern to utilities and regional Independent System Operator. Based on an 115kV disturbance investigation at National Grid, this paper presents an analysis of under-performance on a ground distance function of a line protective relay when a non-bolted ground fault occurred on the protected line. The modern microprocessor relays give user multiple choices to select the desired protection characteristics, such as MHO or QUOD shape for ground distance protection. How to properly take this advantage for the microprocessor relay could be a challenge for utility engineers. This paper also discusses and compares the performance/coverage of MHO and QUAD under different application scenarios.