A Single-phase Fault Line Selection Method For Resonant Grounded System Based On Transient Information

The neutral Non-effectively grounded system is widely used in China's distribution network,which includes neutral-ungrounded system and resonant grounded system.The neutral Non-effectively grounded system can supply power with high reliability.When single-phase ground fault occurs,the line voltage keeps symmetrical,which means the fault has no effect on power supply.With the development of the city,the scale of the distribution network becomes bigger and the system capacitive current becomes bigger.Big capacitive current means that a grounding arc may come out easily.To put out the arc,resonant grounded system is widely used.However,there are a lot of problems about resonant grounded system fault line detection.The line detection accuracy of some applied methods is still low.To improve the accuracy is of great importance for the security of power system.This paper first introduces the existing resonant grounded system single phase fault line selection methods,points out the existing problems at the same time.Then analyzes the characteristics of single phase to ground fault in resonant grounded system,especially the influence of fault switching angle on transient capacitance current and decaying DC component.To solve the problem of low accuracy of fault line detection in resonant grounded system,especially in small switching angle conditions,a new fault line detection method is proposed in this paper.The new method takes advantage of Hilbert transform and ensemble empirical mode decomposition method in the aspect of signal time-frequency analysis.The new method collects the zero sequence voltage of the system,the zero sequence current of each line and the current of the arc suppression coil.By computing the transient signal energy of each line,primary result comes out.And by comparing the energy of transient capacitance current with that of decaying DC component,the signal with higher energy is used for final fault line detection adaptively.The simulation results prove that the new method has high fault line detection accuracy no matter fault switching angle,fault location or fault resistance.The problem of low acuracy of fault line detection in small switching angle occations can then be solved.