Islanding detection based on asymmetric tripping of feeder circuit breaker in ungrounded power distribution system

An islanding detection method in ungrounded power distribution system based on single-phase operating mechanisms of the circuit breaker (CB) is proposed in this paper. When CB opens three phase circuits to form an island, one phase circuit is opened firstly and the other two phase circuits are opened secondly after certain duration. During the period when only one phase circuit is opened, negative sequence voltage with certain duration is obtained at DG side because of the asymmetric operation of the system. After all three phase circuits are opened, the voltage variation direction of the two phases that are secondly disconnected from the grid follows the voltage variation direction of the firstly disconnected phase. Based on the above voltage characteristics, an islanding detection scheme is proposed to identify genuine islanding from system disturbances. The performance of the proposed scheme is tested in PSCAD/EMTDC using a 10 kV distribution network with synchronous DG interconnection. Simulation results demonstrate the proposed method is effective and reliable to detect islanding formation.