The invention, which relates to the technical field of
circuit protection, provides a single-phase ground fault diagnosis method on various conditions of a cable, an
overhead line, and a parallel-
serial line. The method comprises: step a, an opening
delta zero-sequence
voltage at a PT
secondary side is monitored; step b, whether a zero-sequence
voltage occurs is determined; step c, whether the frequency of the zero-sequence
voltage is a
power frequency is determined; is not, a
signal is sent out to respond to a moving element of a
resonance elimination device; step d, three-phase voltage
monitoring data are read; if voltage of one phase or voltages of two phases is / are normal-phase voltages and the voltages of other phases are zero, a PT primary side line-breaking fault is determined; step e, a single-phase ground switch that can be turned on or off normally can be put between a neutral point of the PT and the ground, so that a grounding switch trips and is closed rapidly; and step f, whether the opening
delta voltage exists is determined; if so, a single-phase ground fault is determined; and if not, fundamental-frequency
ferromagnetic resonance is determined. According to the multi-parameter rapid switch fault determination method, the method can be realized simply and reliably; and a fault loop can be disconnected rapidly by using a quick switch, so that accident extending can be avoided.