Method Study On Fault Line Selection In Small Current Neutral Grounded System

The probability of single-phase ground fault is about80%in all fault ofdistribution network. With the increase of power system scale and cable-line mixing line,the phase-to-ground fault current shows an increasing tendency, which could bringabout arc over-voltage and affect the safety of system and equipments. In order toovercome the above-mentioned weakness as well and reduce phase-to-ground faultcurrent and guarantee the reliability of power supply, the neutral point of mostdistribution network in china grounds through arc extinction coil. But because ofcompensation of arc extinguishing coil, the signal which is the criterion of line selectionbecomes fuzzy, and is affected by unbalance current transformer significantly. Thegrounding method will cause failure of partial line selection device, the fault lineselection device for correct operation is facing more and more challenges. The fault linelocation of the distribution system is very difficult in a long time, by the reason of thesize of the steady-state component, the length of line, detuning degrees of compensationgrid, the phase of the fault etc.To this point, the paper makes a thorough research on the theory of line selection atboth home and abroad, and some difficult problems are pointed out. Shortcoming andadvantage of various kinds of line selection theory are discussed. The paper focuses onand simulates the principle of wavelet analysis, correlation analysis, transient zerosequence energy for the most part, and brings up some improved steps to transient zerosequence energy.And the method that uses the variation of transient energy before andafter the tuning is firstly put forward in this paper to be aimed at automatic trackingcompensation system. After analyzing the steady and transient characteristics ofdistribution network when the single-phase grounding fault happens, the paper bringsup a line selection method using extenics which combines the characteristics oftransient zero sequence energy and correlation coefficient of wavelet packetdecomposition,also this method combines reclosing technique.The simulation model ofneutral earthing via arc extinguishing coil system was created by use of MATLAB.Experiments which simulates through different fault line, fault close angle, transitionresistance and fault location, show the validity and rationality of this method.