Method for judging single-phase grounding fault of low-current grounding system

The invention discloses a method for judging a single-phase grounding fault of a low-current grounding system. According to the method, bus zero-sequence voltage, interval three-phase current and zero-sequence current need to be accessed, and whether a grounding fault exists or not is judged according to the zero-sequence voltage; wavelet packet transformation is carried out on the transient three-phase current, the transient zero-sequence current and the transient zero-sequence voltage of the length of the data window of the previous cycle and the latter half cycle of the fault at the grounding occurrence moment; and the directions of the zero-sequence current and the phase current of the characteristic frequency band and the directions of the zero-sequence current and the zero-sequence voltage of the characteristic frequency band, which are obtained after conversion are comprehensively compared so as to identify the grounding fault. The method can be applied to a system of which the neutral point is not gro