Analysis of the Entire Process Characteristics of Single Phase-to-ground Faults in Flexible Grounded Distribution Networks
To further clarify the characteristics of single phase-to-ground faults under flexible grounding methods and provide theoretical basis for the research of new grounding protection principles,an equivalent circuit covering the entire process of ground faults in flexible grounded distribution network is established.The amplitude and phase characteristics of typical fault electrical quantities at various detection points,variation patterns in different stages are analyzed.Compared with situation before the neutral point grounding resistance is applied,under different fault conditions,the current fault point always increases,and the system zero sequence voltage and zero sequence current of healthy lines always decrease.However,the zero sequence current of fault line increases firstly and then decreases with the increasing of the fault point grounding resistance.This is not entirely consistent with the original intention of implementing flexible grounding methods,which explains the reason why the traditional small-resistance zero-sequence overcurrent protection commonly used in the field is not as effective as expected.Both digital simulation and on-site manual experiments have verified the correctness of the conclusions drawn in this paper.
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