Wavelet Analysis For Single-phase Fault Line Selection In Small Current Grounding System

Fault detection in distribution network is being a worldwide knotty point for a long time. In this paper, a new method of fault detection is presented based on the deeply studying of phase-to-ground fault transient conditions and the multiband analysis technology.In this method, wavelet packet with the advantage of time-frequency zoom is used to decompose each line's post-fault transient current with proper bandwidth. In view of maximum energy, the characteristic band, in which the transient capacity current is most concentrative and the feature of fault is most explicit, is adaptively taken out for each line. Based on the principle that the fault line's phase of transient capacity current are different from normal line's, the fault-line will be found out by contrasting polarity of each line's wavelet packet decomposition coefficient in all characteristic bands.To eliminate the dead zone of fault detection, which appears when the fault is occurring with phase voltage near to zero, there is a creative method proposed in this paper, which use wavelet with signal reconstruction arithmetic to analysis the reconstructive signals of direct current and fundamental current in each line's zero sequence current. Based on the concept that there would be lots of transient inductance direct current contained in zero sequence current of fault line in this fault condition, the energy ratio of these two reconstructive signals in fault line is different from which in normal line, then the faulty line would be find out.Lots of ATP and SIMULINK simulations show firstly that the proposed method can choose the fault line more exactly and reliably, for the fault features can be utilized more sufficiently by performing fault detection in...