Reserch For The Characteritics And Line Selection Of Single Phase Grounding Fault In Medium Voltage Network

One of the main grounding modes in distribution network is neutral point via arcsuppression coil grounding, it helps to improve the reliability of power supply, but thedifficulty of fault detection is increased due to its small fault current. In neutral point via arcsuppression coil grounding system, the problem of single phase grounding fault line selectionis an important research topic in power system protection, and its also is a tough problem.The model of instantaneous sequence network when single phase grounding fault occursin neutral point via arc suppression coil grounding grid is built to research the transienttransition process of single phase grounding fault characteristic quantity. Instantaneoussequence network model can describe both transient and steady-state process in the singlephase grounding fault. Analyzing the model can obtain the mathematical expression and itsvariation of some characteristic quantities such as zero-sequence voltage, real part ofinstantaneous positive sequence current, imaginary part of instantaneous positive sequencecurrent and grounding current, it provides a theoretical basis for the study of single phase faultline selection.In order to verify the correctness of the obtained characteristic expression andcharacteristic of law a simulation model is built through MATLAB, on which differentgrounding resistance, fault closing angle, fault line and arc suppression coil compensationmethod are simulated. Through a large number of simulations can be found the real part ofinstantaneous positive sequence has a great difference between the fault and non-fault branch,it is not obvious between the non-fault branches, and this feature is independent of influenceof various factors.According to the characteristic of instantaneous fault characteristic quantity which obtained in theory analysis and simulation, using correlation analysis method to analyze thesimilarity of characteristic quantity in fault and non-fault phase, so as to achieve the purposeof single phase fault line selection. Using the transient value of the real part instantaneouspositive current which is obtained in the first cycle after single phase grounding faultcorrelation analysis. Through constructed the correlation matrix, significantly relativedifference, line selection vector and range to represent the difference of the instantaneous realpart positive sequence current between fault and non-fault line, and then electing the faultbranch.