| Lightning strike is the main type of fault that causes the transmission line to trip-out.The lightning protection of the transmission line depends on the perfect lightning risk assessment system.At present,the main indicator for evaluating the risk of lightning damage on transmission lines is the lightning trip-out rate.Therefore,accurately calculating the lightning trip rate is of great significance for the safe and stable operation of transmission lines.Lightning parameters are important basic parameters in the calculation of lightning tripout rate of transmission lines,including ground flash density,lightning current amplitude probability density function and lightning current waveform.With the completion of Chinese lightning location system,the statistical work of lightning parameters has gradually started.At present,some achievements have been made,but there are still some problems in statistical accuracy and rationality.In view of the deficiencies of related research,this paper takes lightning parameters as the research object,and studies how to improve the accuracy of lightning trip-out rate.The main contents are as follows:Firstly,the rationality of using the grid method to calculate the ground flash density of the transmission line corridors is analyzed.It is pointed out that the statistical results of the grid method may have a large difference in the ground flash density of adjacent towers.Aiming at this problem,a statistical method based on the statistical ground flash density according to span and the statistical ground flash density according to the tower is proposed to calculate the ground flash density of a certain transmission line.The statistical results show that the ground flash density according to the tower statistics and the span statistics shows a continuous change mode,and there is no possibility that the difference in flash density between adjacent towers is large.Secondly,based on the data of the lightning location system of Hainan Power Grid,the two methods of parameter estimation and non-parametric kernel density estimation are used to fit the lightning current amplitude probability density function.The fitting results show that the generalized extremum distribution has the smallest root mean square error in the distribution model of all parameter estimates,and the fitting root mean square error of the nonparametric kernel density estimation is smaller than the fitting result of the parameter estimation,but the probability density function is more complicated.The back flashover tripout rate and the shielding failure trip-out rate of the typical tower are calculated by using the different lightning current amplitude probability density function.The calculation results show that the lower the voltage level,the greater the influence of the lightning current amplitude probability density function on the lightning trip-out rate.Finally,the mathematical models of the three commonly used lightning current waveforms are compared to obtain a conclusion that the Heidler wave waveform is closer to the typical negative first-time lightning current waveform.The genetic algorithm is used to solve the problem of parameter estimation of Heidler wave.The calculation results show that the Heidler wave parameter estimation result obtained by genetic algorithm is basically consistent with the calculation result of F.Heidler's graphic method.From the theoretical and simulation aspects,the influence of various parameters of Heidler wave on the lightning withstand level of transmission lines is analyzed.The theoretical analysis shows that the steepness of the lightning current head has a direct impact on the lightning back flash withstand level,but has little effect on the lightning shielding failure withstand level.The simulation results show that with the increase of the time constant of the wave head,the lightning back flash withstand level gradually increases.With the increase of the lightning current steepness factor,the lightning back flash withstand level gradually decreases. |
PDF Full Text Request