Transient Current's Energy Spectrum-Based Faulty Type Identification Method In EHV Lines

With the rapid development of power industry and the improvement of large power grid, extra high voltage transmission lines (EHV) have became an important part of large-scale power system. In order to avoid system stability being destroyed when power grid fault occurs, relaying protection should operate properly according to various fault type. Thus, the accuracy and rapidity of relaying protection have become more and more important.Wavelet Transform in Time-Frequency at the same time the nature of a good localization, it is a powerful tool for Analysis of transient signal. So wavelet theory in power system is widely used as Power Quality, Protective Relaying, Transient Analysis, High-voltage Discharge. Original signal Wavelet Transform's maximum norm corresponding to the signal singularity,and wavelet coefficient includes energy Time-Frequency localized information, so Wavelet Theory provide a powerful mathematical tool for research on transient component under power system fault state(transmission line fault state power system oscillation state etc).Transient Protection fast response to fault, will not be affected by Transition Resistance, System Oscillation, Current Transformer Saturation. Transient signal includes a large amount of information which reflect the nature of the power system failures, current's energy in different frequency is different, it provides the basis for fault analysis. System will produce high-frequency transient current transient current signal from the fault lines of positive and negative directions when the event of the failure of transmission lines. Transient high-frequency signals are sampled after the formation of features as the original data. After the wavelet transform available to high-frequency discrete wavelet transform coefficient that reflects the original signal high-frequency details of the energy coefficient. Coefficients of the details have been the norm to deal with the current energy equivalent norm. Its characteristics as a criterion of fault type. In this paper, pre-and post-fault transient signal are transformed by using db3 wavelet, and identification criterion is constructed according to wavelet energy spectrum data. Then, a transient current's energy spectrum-based faulty type identification method in EHV lines is presented. 500kV power transmission line model in Matlab platform is constructed to test the proposed method under different transmission line fault types and different initial conditions. Simulation results show that the proposed method is effective. Sub-stations should be pre-processing system in real-time pre-processing and fault data uploaded to the control center. This will help to reduce transmission congestion event channel to improve the efficiency of fault diagnosis. Its transmission line distance protection of great significance Oscillation and fault current waveform has a large peak as well, however,oscillation and fault have their own characteristics,so their currents are different in various frequency bands. Wavelet coefficient's maximum norm could reflect specific frequency domain transient component changes, so power system fault and the oscillation can be identified by wavelet coefficient's maximum norm. Simulation tests show that the identification method is feasible.