A novel protection scheme for two-phase faults in power distribution system with neutral ungrounded

A novel protection scheme for two-phase faults in power distribution system with neutral ungrounded is presented. The feasibility of tripping single-phase circuit when a phase-to-phase or two-phase-to-ground fault occurs is studied with induction motor loads as the focus. The presention first theoretically analyses the effect of an induction motor run with one phase cut off. Then a real power distribution system model with 110 kV, 35 kV and 6 kV voltage levels is built in the time-domain simulation program PSCAD/EMTDC. Three feasibility criteria are proposed for motors in continuous operation with single-phase opened. Finally, the novel protection scheme is testified in simulation with protection time and reclosing time as variables respectively. The results verify that the scheme is feasible and that the power supply reliability is improved.