Research On Characteristics Of Gas Discharge In Airflow Environment

Power system and high speed railway are national major needs.Power system is the basic guarantee of national energy supply,high speed railway shoulders the important task of national transportation.Their safe operation and rapid development are the strong guarantee for the sustained growth of national economy and the improvement of national comprehensive strength.The external insulation discharge for transmission line in the wind and sand environment is a problem that cannot be neglected with the cross-region and high-voltage operation of the UHV backbone network.In addition,the strong airflow(up to100 m/s)caused by high-speed train may be the key factor to induce the abnormal flashover of external insulation on the roof of the high speed train.In conclusion,gas discharge in airflow environment has become a key scientific problem that needs to be solved.At present,the characteristic and mechanism of gas discharge in airflow environment are not clear and the relevant theories are also lacking.Therefore,it is difficult to complete the calculation and analysis of gas discharge in airflow environment.As a result,the external insulation protection and design in airflow environment faces severe challenges.Therefore,this paper attempts to explore the characteristics and mechanism of gas discharge in airflow environment,and establish the model of gas discharge in airflow environment and present the breakdown criteria based on the theories of gas discharge and fluid,meanwhile combined with the experiment,simulation and theoretical analysis.The main research contents and conclusion are follows:Firstly,the main characteristics and mechanism of gas discharge in airflow environment were experimentally investigated by using the needle-plate electrode and needle-needle electrode.It was found from the experiments that the breakdown voltage of the needle-plate air gap first increases and then decreases because of the comprehensive influence of the airflow density,electron free path in the field direction,and collision ionization probability.In addition,the airflow direction causes an obvious polarity effect,that is,the headwind effect weakens the discharge and increases the breakdown voltage,and the downwind effect strengthens the discharge and decreases the breakdown voltage.It was revealed that the comprehensive influence of the airflow density,electron free path in the airflow direction,and diffusion radius of electron was the essential reason that caused the polarity effect of gas discharge in airflow environment.It was known from the above experiments,the changes of the electron free path in the field direction caused by the deflection effect,the ionization probability caused by the blowing away effect,and the electron free path caused by the density effect affected the gas discharge in airflow environment.Based on the conclusions,the basic preconditions of the model were firstly established,and then the analytic expressions that describe the relationship between the ionization coefficient and space charge and airflow velocity under the comprehensive influence of the deflection effect,blowing away effect and density effect were obtained.On the basis of the theories of Townsend discharge and streamer discharge,the model of gas discharge in airflow environment was established,and the breakdown criteria was also presented.Thereafter,based on the fluid and kinetic theory,and combined with the experimental results,the rationality of model assumption and validity of model calculation were verified.Based on it,the breakdown voltage of air gap exceeding the range of experimental airflow velocity was predicted,and the influence rule of the airflow on Paschen curve was also revealed.Meanwhile it is found that the difference of the field distribution,space charge and drift velocity between the uniform field and the non-uniform field is the reason causing the difference of the gas discharge in airflow environment.