Research on the Fault Characteristic in Non-effectively Grounding Distribution Network with a Single-Phase-to-Earth Fault Based on Hilbert-Huang Transform

According to the obvious transient characteristics at the beginning of the fault in the non-effectively grounding distribution system, a new method, based on Hilbert-Huang transform(HHT), is proposed to extract the non-power frequency transient current from the zero-sequence current in distribution networks with a single-phase-to-earth fault. HHT is used to get the amplitude and phase angle of the zero-sequence current at the beginning of the fault. The non-power frequency currents, which have obvious characteristics, are calculated when power frequency currents are extracted from the zero-sequence currents. A neutral non-effectual grounding distribution network model is established with the Matlab/Simulink and simulated in many cases. The simulation results suggest that the non-power frequency current of the fault line, extracted with HHT, have a contrary polarity as the currents of the non-fault lines and have a more amplitude than each of the other non-fault lines at the one tenth of the wave period time after the fault occurs. Moreover, the non-power frequency current keeps the same transient characteristics when the different short circuit time, arc resistance, fault distance or the compensation rate is changed. Thus, it can be used to rapidly select and protect the fault line with the single-phase to ground fault in distribute network.