Implementation of a New Algorithm to Detect Turn-to-Turn Faults in Shunt Reactors and Identify the Faulted Phase

Detection of the turn-to-turn fault in shunt reactors has been a challenging task for P&C engineers. This is because turn-to-turn faults create very small changes in the currents and voltages that the relay measures, where existing methods don't have enough sensitivity to detect such faults. Undetected failure will result in loss of the entire reactor phase. Recently, a new algorithm, allowing for much better sensitivity, was proposed providing a reliable way to detect turn-to-turn faults and reliably identify the faulted phases [3]. The new algorithm makes use of the negative sequence and the positive sequence voltage and current measurements to develop a differential scheme to sensitively detect shunt reactor internal faults. With the advantage of expanded programming capabilities in modern relays, Xcel Energy was able to program this algorithm and successfully test it by playing back records captured during several shunt reactor failure events. The new algorithm was able to identify the turn-to-turn faults and the faulted phases simultaneously, for all the events indicating the superiority of this algorithm over the existing techniques. The algorithm remained stable for several cases of shunt reactor energization and external faults. The algorithm has been deployed in the field for evaluation. This paper will present Xcel Energy's approach to achieve better shunt reactor protection utilizing this algorithm and share their findings.