The Analysis Of Transient Mechanism In Single Phase Grounding Fault

The study of fault transient characteristics of single phase earth fault is very important for neutral grounding modes and the related technologies in distribution network. Previous study mainly concentrated on transient signals based fault detection, as to the researches and conclusions on the transient mechanism is very limited. The scanty transient mechanism is described as the charge-discharge of distributed capacitance of lines, it is rough and untested. And it only reflected the partial transient resonance process, it is inaccurate and incomplete.A high precision fault model based on distributed parameters feeder including both sides of fault point was established in this paper. On the basis of analyzing phase-frequency characteristics of detecting impedance, the LC resonance mechanism of single phase earth fault transient in non-solidly earthed network was proposed. Transient process can be described as the superposition of series resonances in single line, series resonances between line-mode and zero-mode networks, parallel resonances between two sides of fault point within the same modulus, parallel resonances between different sound feeders within the same modulus. The LC resonance mechanism proposed in this paper can be used to analysis all resonance mechanism and energy exchange law in whole frequency domain.Transient current produced by series resonance between line-mode and zero-mode network contains clear fault location information, it can provide the basis for fault detection technology.Changes of parameters in the distribution network may produce new conditions or change previous resonance conditions even eradicate partial resonances. Specific to the main resonance process which shares the largest energy in whole frequency domain and can reflect basic characteristics of transient process, the influence of the distribution network parameter changes are analyzed. Among them, the longest line length and upstream length of fault point have a greater influence on the main resonance frequency.In view of the traditional capacitance charging and discharging mechanism, charge and discharge model of single phase system and three phase system model are established in this paper. It can concluded that main resonance component of charge and discharge model of single phase can not correspond to each resonance components of the entire network model, charge and discharge model of three phase system can not completely separated charging process and discharging process because of three phase coupling effect. The irrationality of tranditional capacitance charging and discharging mechanism is preliminary verified.The reasonability and correctness of transient LC resonance mechanism, change law of transient main resonance frequency with changes of distribution network parameters and the irrationality of tranditional capacitance charging and discharging mechanism are verified by program calculation and simulation.The achievements of this paper contribute to grasp the transient mechanism of single phase earth fault overall and accurately. They not only provide theoretical basis for the development of fault detection and protection, overvoltage protection, ground compensation and the selection of neutral grounding mode of distribution network, but also provide basic for the research on related technologies in smart distribution network.