A universal solution to the detection of high impedance earth faults – the ultimate retrofit

Reliable detection of high impedance earth faults on MV networks continues to be a major challenge on distribution networks worldwide. Conductors down on high resistance surfaces present person safety risk issues and increasingly, an elevated risk o f wildfire ignition. There is an absence of reliable solutions for the detection of such earth faults. There is no universal solution that works satisfactorily regardless of the system neutral treatment in use, for both 3-wire and 4-wire construction and for any load connection (three phase, phase-phase and phase-neutral). Any potential solution needs to be readily retrofittable to legacy installations to supplement or replace existing earth fault protection networks. The innovation outlined in this paper i s a completely new earth fault protection relay platform. It applies well established fundamental frequency detection algorithms, a new augmentation of the fault inception transient detection approach plus a novel signal comparison algorithm. For maximum ease of retrofitting to existing networks, standalone relays per feeder are employed (rather than centralised), with a clip-on CT option to avoid breaking into existing CT secondary wiring. Sensitivity of at least 5 kΩ, up to in excess of 10 kΩ (depending on accuracy of instrument transducers used), have been achieved.