Simulation of air gap discharge properties and charge evolution law under typical electrode structure

Air gap discharge is usually an important cause of insulation failure in power equipment. In this work, the discharge characteristics of the air gap were investigated experimentally under three typical electrodes. The simulation model of the air gap discharge under the typical electrodes is established. Furthermore, the evolution of electron density and space charge during the discharge process over time was explored theoretically. The experimental results show that the breakdown voltage of the ball–ball electrode is significantly higher than that of the needle–plate and the rod–plate. Moreover, it increases more with the increase in the discharge gap than that of the other two electrodes. The simulation results show that the evolution law of discharge caused by different electrode types differs greatly during the development of the air gap discharge. The needle–plate and the rod–plate electrodes gathered positive polarity space charge at the head of the streamer, and the ball–ball electrodes showed an upward leader at the grounded electrode, gathering negative polarity space charge and accelerating the development of the streamer. In addition, the maximum electric field for the needle–plate and the rod–plate electrodes moves gradually from the electrode surface to the streamer head, owing to the effect of space charge. The work is of great significance in guiding the analysis of discharge faults in power equipment.