Research On Small Current Neutral Grounding System Based On Wavelet Packets And Comparation Of Energy

Neutral un-effectual grounded system are widely used in power distribution network in china. The single phase-to ground fault happens most frequently in distribution network. Due to the small fault current and unobvious fault features after single phase-to-ground fault, it easily leads to the wrong detection of the fault line. Especially for the arc suppression coil grounded system, the remnants current of the grounded point on fault line is very thin, and the phase is somehow changed, thus, it's more difficult to detect the fault line in Peterson-coil grounded system. The problem of fault line detection has been studied for years in our country and abroad , however, it still has not been solved perfectly, which has seriously blocked the development of reliability of power supply and automation lever of distribution network.Firstly, in this paper, the stable and transient features of single phase-to-ground fault in un-effectual grounded system are deeply researched and analyzed in theory, and combine with the theory wavelet packets, a new way is putted forward for detection of the fault line based on wavelet packets and the compare of energy. First parallel a medium resistance instantly with the arc suppression when the fault is happening to increase the transient characteristic, and then obtain all the energy of every line by integral operation to preparatory detect the possible line, in the end , on this base, decompose all the transient zero sequence currents in every line by separation based on nicer separate frequency characteristic of wavelet packets, detect the polarity and size of differential coefficient for every zero sequence current ,when the line which's polarity is contrary to others and it's size is maximum, then it can be detected truly that it is the fault line.The energy integral and the rising wavelet packets is combined in a creative way in this paper.It is testified by a great deal of examinations with simulation that this way can more efficiently use the transient information in the process of fault , it can overcome the failure in the identify of fault information because of disturbers and measure errors, it can greatly increase reliability of fault detection for line, it also doesn't influenced by transient resistance and the initial phase of fault and the compensatory size of neutral , it can surely and unfailingly detect the fault line in every stated instance ,so this way has wide applied foreground and good applied worth.