Research On The Identification Method Of Back Flashover And Shielding Failure Over-voltage In Transmission Lines

Domestic and international operating experience show that lightning strike is the main reason for the tripping of transmission lines.According to the different type of lightning strike,it can be divided into induction lightning strike and direct lightning strike,induction lightning strike can have a significant impact on transmission lines of 35 kV and below,but direct lightning strike has a major impact on transmission lines of 35 kV and above,as a result,direct lightning strike is the main target of the research on lightning protection.Depending on the different mechanism of lightning strike,direct lightning strike can be divided into back flashover and shielding failure,and their protective measures are not the same,back flashover is mainly related to the grounding resistance,and shielding failure is mainly connected with the protection angle of ground wire.In the aspect of lightning protection of transmission lines, although the protective measures have been taken,but the protective effect is not ideal,the main reason is that there is no corresponding protective measures against the specific type of lightning strike.So accurate identification of back flashover and shielding failure in transmission lines,and taking reasonable protective measures is of great significance to ensure the safe operation of power system.In order to realize the identification of back flashover and shielding failure over-voltage, firstly,in this paper,lightning current model,tower model,insulator string flashover model and transmission line model are selected,and simulation models of 110 kV and 750 kV transmission line are set up,a lot of back flashover and shielding failure over-voltage waveforms are obtained by simulation calculation,by means of analyzing the mechanism of back flashover and shielding failure,and comparing the waveforms of back flashover and shielding failure over-voltage,it is found that the back flashover and shielding failure over-voltage wave fronts are of different polarity,when back flashover over-voltage occurs, the wave front is of normal polarity,when shielding failure over-voltage occurs, the wave front is of negative polarity.Therefore,the use of the polarity of back flashover and shielding failure over-voltage wave fronts as recognition characteristics is proposed.In order to obtain the polarity of back flashover and shielding failure over-voltage wave front,in this paper, the quadratic b-spline wavelet is selected,and using static wavelet transform to obtain the multi-resolution decomposition of back flashover and shielding failure zero-module voltage and the modulus maxima of back flashover and shielding failure zero-module voltage wave front,when back flashover over-voltage occurs,the modulus maxima is of normal polarity,when shielding failure over-voltage occurs,the modulus maxima is of negative polarity.Finally,the identification criterion is constructed by the modulus maxima of zero-module voltage wave front and the maximum value of zero-module voltage, and the validity of the identification criterion is verified by the simulation calculation. Identification results show that the constructed identification criterion can accurately and effectively identify back flashover and shielding failure over-voltage.