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Online criterion and identification of single-phase ground fault with high resistence in distribution network

Zhou Feng;Zhu Rui;Wang Chenguang;Wang Bingquan;Liu Jian;School of Electrical Engneering and Automation,Harbin University of Science and Technology;  
The high-impedance grounding fault of a distribution network in neutral ungrounded system occurs frequently.When the fault occurs,short-circuit current value is small,which caused unobvious fault characteristic and difficulty online identification.So it will be hard to notice the fault in initial stage and easily falls into a serious fault.Through studying the transient process of single-phase grounding fault,it is founded that the transient capacitive current of the fault will caused significant higher harmonics in zero-sequence voltage waveform.The above viewpoint was proved by the spectral analysis of the zero-sequence voltage after the single-phase high-impedance grounding fault happening in 10 k V distribution network's simulation.Thus,the higher harmonics can be used as high-impedance grounding fault online identification characteristic harmonics.In order to ensure the uniqueness of the characteristic harmonics,the simulated contrastive analysis of the zero-sequence voltage was compared between other fault types and sudden add-subtract load condition.For further exploration to the law that how the parameters of the fault affects the characteristic harmonic,the fault is simulated at different phase angles and different fault resistances.The results show that when the fault occurred at 90 ° phase angle of phase voltage,the amplitude of characteristic harmonic is maximum,ranked about 4% ~ 9% of the fundamental amplitude.And the amplitude decreases regularly while the fault resistance increasing.With obvious feature,the characteristic harmonic is qualified for the accurate singlephase high-impedance grounding fault identification.Thereby,the method provides a new idea for the research of device for the power distribution network fault identification.
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