Study On Zinc Oxide Arrester With Gap In EMU

During the operation of EMU,the explosion accident of zinc oxide arrester occurs frequently,which seriously affects the safe and reliable operation of the train.Through investigation,it is found that the long-term harmonic overvoltage of OCS is the main cause of lightning arrester failure.Therefore,this dissertation proposes a solution of adding gap structure and current limiting resistance to the original gapless zinc oxide arrester,so as to reduce the leakage current flowing through the arrester body under harmonic overvoltage,so as to reduce the temperature rise of the arrester under harmonic overvoltage,and then reduce the probability of thermal collapse failure of the arrester.Taking EMU arrester as the research object,this dissertation first designs the structure of series gap arrester(series gap GMOA,Gap Metal Oxide Arrester)and gap arrester with parallel resistance(parallel resistance GMOA),and establishes the arrester circuit model and overvoltage simulation model.Through theoretical simulation,the protection characteristics of gapless arrester,series gap GMOA and parallel resistance GMOA under operating overvoltage and standard impulse current are compared and studied.The results show that under the switching overvoltage of the circuit breaker,the amplitude of the cut-off overvoltage generated by the series gap GMOA during the gap action can reach about 142 k V,and it is difficult to reduce the cut-off overvoltage by improving the gap structure;The cut-off voltage of parallel resistance GMOA is significantly lower than that of series gap GMOA during gap action,and its cut-off overvoltage decreases with the number of current limiting valves or the decrease of current limiting linear resistance.Considering that the current limiting resistance is too small to effectively limit the leakage current flowing through the zinc oxide valve of the main body of the arrester under harmonic overvoltage,through comprehensive analysis,it is concluded that when the number of zinc oxide current limiting resistors in the parallel resistance GMOA is 2 or the current limiting linear resistance is 1～2MΩ,it is better.The comparative study shows that under the standard impulse current,the steep wave,lightning and operating impulse residual voltage of gapless arrester and gapless arrester are 114.93 k V,105.00 k V and 83.99 k V respectively,the 1m A power frequency reference voltage of gapless arrester is 42.30 k V,and the 1m A power frequency reference voltage corresponding to GMOA with two zinc oxide current limiting resistors and 1.5MΩ linear current limiting resistors is increased to 48.90 k V and 44.60 k V respectively.Secondly,based on the variation law of the electrical characteristic parameters of the arrester obtained from the experiment,the electrothermal model of the arrester is established to study the leakage current and temperature rise of the arrester under harmonic voltage.The electrical characteristics of zinc oxide resistor are experimentally studied,and the variation laws of its conductivity and volt ampere characteristics under different voltages and frequencies are obtained.On this basis,the circuit model of arrester under harmonic voltage is studied,and the electrothermal model of arrester is established by COMSOL multi physical field simulation software,The leakage current and temperature rise of gapless arrester and parallel resistance GMOA under different amplitude power frequency voltage and harmonic voltage are studied.The results show that the leakage current and temperature rise of gapless arrester increase significantly with the increase of voltage amplitude and frequency.Using parallel resistance GMOA can effectively limit the leakage current and temperature rise of arrester under harmonic overvoltage,and the limiting effect of GMOA with linear resistance is more obvious.When the effective value of voltage is 34 k V and the harmonic frequency is 2050 Hz,the temperature rise of gapless arrester is 44.5℃,the temperature rise of zinc oxide parallel resistance GMOA is 37.7℃,while the temperature rise of linear parallel resistance GMOA is only 32℃.Finally,considering the protection and withstand characteristics of the gap arrester,the optimal design scheme of the gap arrester is given through theoretical analysis and research.The partial voltage characteristics of the optimized arrester gap under the working conditions of power frequency voltage rise,harmonic overvoltage and power frequency superimposed harmonic are experimentally studied,and the partial voltage ratio and leakage current under different working conditions are obtained.Compared with the leakage current under harmonic overvoltage obtained by simulation,the effectiveness of the optimized design scheme of arrester with gap to improve the withstand characteristics of arrester body under harmonic overvoltage is verified.