Research On The Characteristics And Mechanism Of Positive Leader Restrike

The leader Restrike is a common discontinuous development process arise in positive long air gap discharge.Due to the insufficient spatio and temporal resolution performance of the previous experimental observation methods,the in-depth study of leader Restrike was severely restricted,and led to the fact that the Restrike was basically not considered in the existing simulation models of positive long air gap discharge.Based on the long gap discharge synchronous observation platform with high spatial and temporal resolution,this paper using the experimental observation methods of optical,electrical and thermal,and combined with modeling and simulation methods to focus on the characteristics and physical mechanism of leader Restrike in the positive long air gap discharge process.Firstly,by building a long air gap discharge synchronous observation platform with high sensitivity and high temporal and spatial resolution,the refined experimental observation of positive leader Restrike phenomenon was carried out under 10 m rod-plate gap with the wavefront of 1000 ?s and 2500 ?s,respectively.Based on the experimental observation results,the optical and electrical characteristics of the two types of leader Restrike defined by the predecessors and the leader branching phenomenon were analyzed,and the optical and electrical characteristics of the positive leader Restrike were clarified.Furthermore,it was found that the discharge and luminescence of the leader channel start from the tip of the electrode when the positive leader Restrike occurs,which made up for the lack of previous understanding of the optical and electrical characteristics of the positive leader Restrike phenomenon,and provided important experimental data for the further study of the physical process and mechanism of the leader Restrike.Secondly,in view of the lack of any discharge and luminescence characteristics of the channel in the relaxation phase before the Restrike,a discharge experiment platform with a high-speed quantitative schlieren system as the core was designed and constructed.The positive discharge observations with the gap distance of 140 cm and the wavefront time of160 ?s and 210 ?s were carried out,and the spatiotemporal evolution characteristics of the thermal morphology of the leader channel in the relaxation phase before Restrike were obtained.The observation results showed that during the relaxation phase,the gas density of section I of the leader channel near the electrode tip gradually returned to the ambient gas density,and when the lead Restrike occured,the electrode tip reconnected to the leader channel again.Which further indicating that the discharge start from the tip of the electrode when Restrike occurred.Under the experimental conditions with the wavefront time of 210 ?s,the migration and elongation of the lead channel in the relaxation phase before Restrike were discovered.Based on the Schlieren pictures,the process of calculating the radial distribution of the gas temperature of the leader channel using the inverse Abel transform of the cubic spline function method was proposed,and the calculation results of the calculation example showed that the axial temperature of the leader channel was the highest,and the temperature had a Gaussian distribution in radial direction,which decreased with the increase of the relaxation time.Finally,based on the optical,electrical and thermal observation results of Restrike,the physical process and mechanism of the positive leader Restrike were proposed,and a multi physical field model of the spatiotemporal evolution of the leader channel in the relaxation phase before Restrike was established,and the validity of the model was verified by the experimental observation results.Based on the established multi physical field model,by changing the initial conditions and parameters such as the space charge distribution,the applied voltage rise rate,the charged particle density distribution of the leader channel,and the initial temperature of the leader channel,the spatiotemporal evolution characteristics of the leader channel before Restrike were simulated.The results of the simulation showed that:the gas density recovery length of section I of the leader channel was obviously negatively correlated with the angle of the space charge zone,the positive ion density in the channel,and the initial temperature of the channel,the elongation of the leader head was obviously positively correlated with the increase rate of the applied voltage and the channel positive ion density;the gas density recovery length of section I of the leader channel near the electrode tip and the migration and elongation of the leader head were all caused by the interaction of the ion migration in the channel and the thermodynamic process of the neutral gas in the channel.