Plasma Characteristics of Positive Leader Inception and Development
Peng Changzhi1, Dong Xuzhu1, Zhao Yanpu1, Li Zhijun2, Zheng Yu1
1. School of Electrical Engineering and Automation Wuhan University Wuhan 430072 China; 2. State Key Laboratory of Environmental Protection for Power Grid China Electric Power Research Institute Wuhan 430074 China
Abstract：Long air gap discharge is similar to lightning discharge, which is known as atmospheric plasma. One of the primary processes of long air gap discharge is leader discharge. Despite extensive experimental and simulation work related to leader discharge has been carried out, the conditions for leader initiation remain unclear. In this study, we use experimental data and numerical model to investigate the favorable conditions for leader inception. First, a 10m air gap discharge observation system was built. The observation system includes a high-speed camera, a current measuring device, and a voltage measuring sensor. The high voltage electrode was applied four different rise rate voltages. Using the measured current data, the inception time of the leader discharge can be easily classified. The injected charge for leader inception could be obtained by integrating the current with time. Hence, we obtained the minimum amount of injected charge required for leader initiation at various voltage rise rates. Secondly, the measured current of the 10m discharge gap can be used to simulate plasma discharge process. The key physical quantities that influence channel temperature are the magnitude and duration of the current in the discharge channel. By using the experimental current as the input of plasma model, the gas temperature in the discharge channel could be calculated. Finally, the micro process and luminous properties of the discharge channel during leader development are then examined. The leader discharge current generally fluctuates within a certain range during the leader development process. The plasma model was used to compute the plasma density and conductivity in the discharge channel. Based on the simplified plasma discharge model, the leader formation process of 10m rod plate gap are simulated under different impulse voltage. The evolution laws of the leader channel's streamer stem temperature, conductivity, and thermodynamic parameters are investigated. The main conclusions are as follows: ① For the 10m rod plate gap, the first streamer discharge injected more charge, and the stem can be easily heated to exceed 2 000K before leader inception. At the same peak voltage, with the increase of applied voltage wave front time, the initial trigger temperature of the leader decreases. ② The initial charge injected by the leader is occasionally less than 1μC. The injected charge of the leader can be as low as 0.66μC. ③ During the development of the leader, the channel temperature is relatively stable, maintained at about 4 000K. The generation of electrons is mainly from thermal ionization, and the conductivity of the streamer stem fluctuates within the range of 1~10S/m.
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2023, Vol. 38 
