Single-phase Ground Fault Location For Hybrid Lines In Distribution Network Based On EWT And Duration Coefficient

With the expansion of the scale of urban distribution lines in my country,a large number of cable lines have been put into use in order to beautify the environment and improve the space utilization rate,which has gradually increased the structure of overhead line-cable hybrid lines in the distribution network.Due to the complicated geographical environment and the high probability of fault occurrence along the hybrid lines of the distribution network,most of the faults are single-phase ground faults.Therefore,it is of great significance to study the method of single-phase grounding fault location for hybrid lines of distribution network to improve the speed of accident maintenance and ensure the reliability of power supply.This paper proposes a fault location method based on EWT and duration coefficient to achieve accurate distance measurement,and provides ideas and methods for solving the problem of single-phase ground faults on hybrid lines.For the problem that the existing hybrid line traveling wave fault location principle is easily affected by the unsynchronized time difference of the detection points,a principle of traveling wave fault location for the hybrid line in the distribution network that eliminates the unsynchronized time difference is studied.Firstly,the propagation law of the modulus traveling wave when the single-phase ground fault occurs in the hybrid line of the distribution network is analyzed.In the case of known fault sections,the distance formulas of the zero mode and line mode wave speed difference of the fault points reaching the detection points at both ends are derived to construct the duration coefficient of the corresponding section.Then the fault distance is expressed as the relationship between the duration coefficient and the length of each line.Through theoretical analysis,it is proved that the fault location principle proposed in this paper eliminates the effect of asynchronous time difference on fault location results.In order to solve the problem of weak single-phase ground fault characteristics and difficult to calibrate the transient traveling wave head accurately,a method combining empirical wavelet transform and symmetric differential energy operator was constructed to detect and calibrate the fault transient voltage traveling wave line mode and zero mode component wave head.The EWT-SDEO traveling wave detection method was used to obtain the normalized energy spectrum waveforms of each modulus of the voltage traveling wave.The moment of the first mutation point in the energy spectrum can be calibrated as the moment when the initial traveling wave head of the fault reaches the measuring end.The simulation compares the detection effect of this traveling wave detection method with the traditional Hilbert-Huang transform traveling wave detection method,and verifies the advantages of this method.A fault location method based on EWT and duration coefficient is constructed,that is,the time when the fault traveling wave reaches the detection point is detected by EWT-SDEO,and the corresponding time domain information is brought into the fault location principle mentioned in this paper to complete the fault location.By building a simulation model in ATP-EMTP to simulate single-phase ground faults in different situations,and using MATLAB to process the data,the effectiveness and adaptability of fault location methods based on EWT and duration coefficients are verified.