Experimental Observation Study On Thermal Characteristics Of Positive Streamer To Leader Transition Process

Positive long air gap discharge is the basis of external insulation of power transmission and transformation systems and lightning discharge physical research,streamer to leader transition process plays an important role in leader inception and breakdown.In order to reveal the complex physical process of energy conversion law between electrical and thermodynamic parameters in the process of positive streamer to leader transition process,the thermal characteristic observation method which is suitable for the streamer to leader transition process needs to be studied first.Aiming at the characteristics and difficulties of thermodynamic parameters observation in the streamer to leader transition process,a method for determining the linear working area of quantitative schlieren system measuring the thermodynamic parameters of leader discharge channel and the adjustment method of imaging symmetry are proposed.A quantitative schlieren imaging system suitable for the measurement of thermodynamic parameters in the streamer to leader transition process was established.A method for enhancing the vertical component of the electric field near the electrode to regulate the initial leader discharge path is proposed.Simultaneous observation of gas density,temperature,current and discharge optical morphology of a single stem discharge channel in the streamer to leader transition process of 1 m long air gap discharge was realized.Under three electrode structures,the thermal characteristics observation experiment of streamer to leader transition process in 1m rod-plate gap discharge was carried out,and the radial distribution of gas density and temperature in the initial leader channel and their evolutionary law were obtained.With the increment of the amount of charge injected into the channel of initial streamer discharge,the change of the center temperature of the discharge channel with time from rising to falling in the dark time period are analyzed.The effects of heat conduction,heat convection and V-T conversion on the gas temperature in the dark region are analyzed.The threshold value of the first streamer injection charge resulting in two types of change of the center temperature of the discharge channel in the dark region time is obtained through experiment,Based on the Gallimberti streamer to leader transition 0-dimensional model,the analysis is carried out.The effects of the initial radius and energy partition coefficient on the temperature variation in the dark region are obtained.It is concluded that the model is only suitable for the discharge in which the temperature rises and the thermal radius is approximately consistent in the dark period.The work in this paper lays the foundation for the establishment of a more comprehensive leader inception model in the future.