| High-speed railway is the main artery of national transportation,and power system is an important infrastructure project to support the economy and people’s livelihood.Their safe and stable operation are of great strategic significance for ensuring national economic development,social stability and even national security.Due to the complex and harsh climate environment in northwest China,the external insulation equipment of power lines and the roof of high-speed trains are exposed to the extreme environment of gas-solid two-phase flow such as wind-sand all the year round,which is easy to cause problems such as discharge and flashover,thus posing a huge threat to the safe and reliable operation of high-speed railway and power system.The dielectric discharge characteristics in a strong wind-sand environment are quite different from those in static gas.At present,the influence factors of the strong wind-sand dielectric discharge are unclear,the relevant theories and standards remain lacking,the discharge process is difficult to describe quantitatively,and the quantitative calculation and effective prediction of the breakdown voltage cannot be realized.Therefore,this thesis focuses on the dielectric discharge problem in a strong wind-sand environment,aiming to explore the influence factors and mechanism of strong wind-sand dielectric discharge,present the model of strong wind-sand dielectric discharge and propose the dielectric breakdown criterion based on the theory of gas discharge,starting from the basic physical process of gas discharge,combining with theoretical and simulation analysis.The main research contents as follows:(1)Firstly,through comprehensively sorting the influence of gas flow and solid-phase particles on the basic physical process of dielectric discharge in a strong wind-sand environment,the main influencing factors and mechanism of gas flow velocity and solid-phase particle concentration/size on the discharge are analyzed from both macro and micro aspects,and the comprehensive influencing factors of wind-sand dielectric on the gap discharge are obtained.It was found that the deflection of main discharge channel,the blowing away of some charged particles,the change in gas density,the distortion of local electric field in the surrounding space,the capture of charged particles by solid-phase particles and the solid-phase particles obstruct the migration of charged particles caused by gas flow velocity and solid-phase particles are the main factors affecting the dielectric discharge process by strong wind-sand dielectric.(2)Secondly,in order to quantitatively analyze the problem of dielectric discharge in a strong wind-sand environment,the basic preconditions of dielectric discharge in a strong wind-sand environment are proposed.Based on Townsend’s theory and streamer theory,the influence mechanism of gas flow velocity and solid-phase particle concentration/size on the discharge ionization process and charge motion process is explored,and the analytical relationship between gas flow velocity,solid-phase particle concentration/ size and electric field strength,ionization coefficient and space charge are obtained.The model of strong wind-sand dielectric discharge based on Townsend’s theory and streamer theory are established respectively,the strong wind-sand dielectric breakdown criterion is proposed,the Paschen’s law of gas breakdown is modified,and it was extended to the theoretical calculation and engineering application of gas-solid two-phase flow dielectric discharge such as wind-sand.(3)Finally,through the simulation calculation of the theoretical model presented,the changing curve of breakdown voltage with gas flow velocity and the modified Paschen’s curve under different solid-phase particle parameters(the concentration of solid-phase particles,size of solid-phase particles and charge coefficient of solid-phase particles)are obtained.Based on this,the influence of gas-solid two-phase flow parameters on dielectric breakdown process was analyzed and discussed,the mechanism of wind-sand two-phase flow parameters on dielectric discharge was revealed,and the changing trend of dielectric breakdown voltage under the combined influence of different gas flow velocity and solid-phase parameters was also predicted. |
