A Novel Adaptive Zero-sequence Current Protection for Low Resistance Grounding System

When a complex multi-line single-phase grounding fault (SPGF) occurs in low resistance grounding system, zero-sequence currents in the faulty feeders would suffer a significant decrease compared to the situation when a single-line SPGF occurs, which will reduce the sensitivity of zero-sequence current relay and may cause the relay tripping failure in severe cases. Therefore, fault analysis for multi-line SPGF was carried out in this paper firstly, and then some important rules were revealed. On this basis, a novel adaptive zero-sequence current protection scheme was proposed, by which the zero-sequence current in multi-line SPGF can be compensated to its value in a single-line SPGF according to the bus voltage in real-time. At last, the proposed protection was verified by a 10kV distribution network established in PSCAD/EMTDC. Simulation results indicate that the proposed protection scheme is not only still applicable to single-line SPGF, but also can detect a multi-line grounding fault effectively, thereby improve the performance of zero-sequence current protection in complex grounding fault.