Calculation Method And Its Application Of Induced Lightning Overvoltage Considering Frequency-Dependent And Non-Uniform Parameters

Lightning accident caused by induction lightning accounts for the vast majority of lightning accidents.In order to improve the safety and reliability of distribution lines and provide valuable reference for lightning protection design,supported by the Fundamental Research Funds for the Central Universities project "Field-Circuit Coupling Problem Hybrid Modeling Method and Simulation Technology"(Grant No 2017MS100).The calculation method of induced lightning overvoltage for overhead distribution lines considering line frequency-dependent and non-uniform parameters is studied.The main research achievements are presented as follows:1.This paper derived a numerical solution method which only takes the voltage along the transmission line as the solution variable and proposed a single variable finite-element time-domain method(FETD)for solving improved telegraph equation of the field-to-line coupling model on the basis of Agrawal field-to-line coupling model.For the typical three-phase overhead distribution lines,the lightning induced voltages on three kinds of line structure which are vertical arrangement,horizontal arrangement and the one with ground line are calculated respectively.Then the accuracy of the method is verified by comparing it with the calculation results of the bivariate FETD method.Furthermore,the efficiency of the method is illustrated by computational complexity analysis,which shows the advantage of the method relative to the bivariate FETD method.2.Based on the non-uniform multi-conductor transmission line theory and Agrawal field-to-line coupling model,this paper derived a single variable finite-element time-domain method for solving improved telegraph equation of the non-uniform multi-conductor transmission line.Then the accuracy of the method is verified by comparing with the calculation results of the bivariate FETD method.For the typical 35 KV overhead distribution lines,the lightning induced voltages which consider the conductor sag are calculated under the condition of different ground conductivity and lightning distance,and the influence mechanism of sag on lightning induced voltage is also analyzed.The results show that the peak value oflightning induced voltage at any point along the three-phase overhead line is reduced after considering sag.Therefore,the effect of sag should be taken into account in the accurate calculation of lightning induced voltage of overhead lines.Furthermore,by comparing the influence of sag ? corona and ground line on lightning induced voltage,the necessity of considering sag of conductor is further explained.The theory and calculation method can be used in actual lightning protection design of overhead distribution lines.3.The calculation of lightning induced voltage considering metal oxide arrester(MOA)is realized.The calculation results show that MOA can not only limit the local phase lightning induction voltage,but also reduce the other phase lightning induction voltage in the two configurations of 35 kV overhead lines.Compared with the phase lightning induced voltage with MOA,the reduction range of phase lightning induced voltage is 71.95%-89.06%,and that of other phases is12.67%-31.16%.Finally,by calculating and comparing the lightning trip-out rates under three different configurations,it is concluded that MOA installed on the highest phase line can provide the best protection.