Fault Line Selection Approach In Resonant Grounded System Based On Integrated Waveform Relative Entropy

In china, the small current neutral grounding system is mainly used in distribution network, which includes the ungrounded system, the neutral point resistance grounding system and the neutral point arc suppression coil grounding system (also called resonant grounded system). When single-phase to earth fault occurs in resonant grounded system, due to the compensation effect of the arc suppression coil, the system fault current is weak, unstably arc and random factors etc, causing a great impact on the fault line selection. Compared with other grounding system, fault line selection of resonant grounded system has been a difficulty in distribution network, and further research about fault line selection method of resonant grounded system has important theoretical and practical significance.This study summarizes the fundamental and the advantage of the various fault line selection methods at home and abroad currently. On this basis, we analyses the steady and transient characteristics of single-phase to earth fault and the impact on system with high transition resistance. It has been obtained that the similarity of the transient zero-sequence current waveforms between fault line and un-fault line was lower than that between un-fault line through analysed zero-sequence network. This study presents a new fault line approach based on integrated waveform relative entropy. Firstly, we use the great time-frequency characteristics of HHT to determine the fault moment more accuracy, further on, make divided-interval in the timeline and the amplitude axis, and histograms-decomposing the fault zero-sequence current waveform. And then through the relative entropy which might reflect the different conditions, we calculate the relative entropy matrix which could reflect the polarity of transient zero-sequence current. Considering the similaity of the locality and integrity in transient zero-sequence current waveform, we define the amplitude matrix which reflects the transient zero-sequence current waveform amplitude information, combined with the relative entropy matrix structure, the integrated relative entropy matrix which reflects the comprehensive fault information. Finally, we use the fuzzy kernel clustering algorithm (KFCM) to distinguish the fault and non-fault lines which could avoid the threshold setting. Meanwhile, this study have done the research of the theory of the arc, selected the model of the arc and analysised the arc characteristics and arc-grounding fault under the premise of verifying the accuracy of the arc model.Simulation model of resonant grounded system is built by using ATP-EMTP. We verify the accuracy of fault line selection approach under the condition of different transition resistance, different fault initial phase angle, different fault lines, arc-grounding fault, two positions grounding, electromagnetic noise interference, disconnection fault, out-sync sampling and. different degrees of compensation A large number of simulation results show that the fault line selection approach offered by this study is accurate and reliable, it not only has high line selection margin, but also has a certain kind of engineering value.