Research On Technology Of Location For Single-phase Grounding Fault In Small Current Grounding System

In China, the range of distribution network is from 10 k V to 66 k V, and these networks generally use small current grounding power systems. The proportion of single-phase grounding fault is more than 70% of the faults in distribution network. At present, workers still switch and patrol artificially to locate the fault point in many places. It costs a large quantity of manpower and resource. So, the effective method of fault line selection and fault location is meaningful for distribution network automation technology.Firstly, the paper summarized the existing method of fault line selection and fault location, and illustrated the characteristics of steady status and characteristics of transient status after single-phase grounding fault occurred in small current grounding power systems. The feasibility of characteristic information being extracted from transient signal is confirmed. And then, different transient characteristics with different angles were compared. So the theoretical basis was prepared for method of fault line selection and fault location.Secondly, to solve the problem of transient characteristics of single-phase grounding fault occurred near the zero-crossing point of phase voltage was different from other conditions, fault angle was regarded as fault condition. Fault angle was examined firstly, and then according to different fault angles with different spectral characteristics, calculation was carried on with purpose. It effectively simplifies the calculation and improves the reliability of the method. According to the analysis above, based on the transient zero-sequence current, the signal within one power frequency would be transformed by db8 wavelet. Wavelet coefficient in corresponding scale was used to calculate the wavelet energy, and wavelet energy in corresponding scale is the criterion for the fault line selection. Matlab/Simulink module was used as the simulation platform. After the change of the parameters, such as the fault resistance, the fault angle and the compensation degree, all of the simulation experiments proved out that the results of this line selection method were correct.Finally, wavelet neural network was used for fault location because of its capability of nonlinearity fitting. Conjunction type of wavelet neural network consisted of loose structure and compact structure was used for fault location in small current grounding power systems. Wavelet energy of transient zero-sequence current of fault line within one power frequency in each scale was chose as characteristic quantity for fault location, and fault distance was chose as output quantity. Base on the fault line had been selected in simulation module, sample set for study training was established and reasonably simplified. Parameters in network were ascertained and process of study training was optimized, so that vibration would be avoided, training was sped up, and network was simplified. Simulation experiments proved out that relative errors of this method were small, it could realize function of the fault location effectively.