Study On The Method Of Detecting Single-phase-to-ground Fault Line For Distribution Network

It is very important to choose a proper earth method to a certain level power system. By now, there are four methods of earth: neutral point un-earth, neutral point directly earth, neutral point earth with resistance, neutral earth with an arc suppression coil. Neutral ungrounded system and earthed system with an arc suppression coil are widely used in our Middle and Low Voltage distribution network. The single-phase to ground fault will happen most frequently in distribution network. Selecting the faulty line as soon as possible will have the vital significance to ensure the systematic normal operation.In the course of deeply studying of phase-to-ground fault transient conditions, we know: Series resonance process and parallel resonance process exist in line. If resonance happened, the resistance's character of detected point for the fault line is complex. Sometimes it is electric capacity nature, sometimes it is inductance nature. It is affected by the number of feeder, the length of each line, and so on. So the relation of the zero sequence current between fault line and normal line is complex.Based on the theory research and compared analysis, according to the favorable property of wavelet packet, this paper advanced to eliminate the band of resonance process and to decompose transient zero sequence current occurred in fault line on a proper bandwidth, so as to obtain zero sequence current in different frequency range. Then, to confirm the bandwidth with the most obvious fault signature based on the view of maximum energy. With the reference to the principle: there are some differences of the polarity of transient capacitive current between faulty line and normal line. When all lines have the same characteristic bandwidth, the faulty feeder can be achieved by comparing the polarity that the wavelet packet decompose transient zero sequence current on this characteristic band. When the characteristic bandwidth is inconsistent for all lines, the fault-line can be found out by this way: to select the characteristic band for each line in turn, contrast scope and polarity of zero sequence current for each line's in this characteristic bandwidth, then the conclusion can be obtained by synthetizing the foregoing comparing result. But, if the breakdown occurs nearby phase voltage zero, the transitionprocess is not obvious, then needs to reconstruct zero-sequence current for each line on the low frequency band, realizes the line selection by reconstruction signal.Lots of simulations show: the method of faulty feeder is given by this paper is less affected by the position of fault ,the time of fault and transition resistance and so on. The higher security and interference killing feature are achieved. It is suitable to neutral earth with an arc suppression coil and neutral ungrounded system. The method has important theory significance and certainpractical value. Figure 40 reference 56...