Experimental research of effects of air pressure and humidity on the leader discharge in the air gap

Summary

The relative density and absolute humidity of gas are always two significant factors which affect the performance of electrical external insulation in atmospheric environment. The previous research, like famous Les Renardières laboratory, mostly reviewed on the gas discharge experiment in the open space without controlling any environmental factors. In this paper, we have set up a gas gap discharge observing and measuring system capable of adjusting and controlling environmental parameters, which can explore effects of air pressure and absolute humidity on the inception and development characteristics of air gap discharge. Our system consists of two main part: first is a set of continuous laser interferometer based on Mach-Zehnder interference principle, which is used to observe and measure the changing process of leader thermal channel; second is a self-designed discharge experimental vessel with adjustable internal pressure that is controlled from 0.1 bar to 6 bar and absolute humidity which is adjusted in the range of 2.6 g/m3 ~ 16 g/m3 (15%~95% relative humidity). The length of air gap discharge is 40cm, and the applied voltage is 250/2500µs switching impulse voltage of 210~346kV amplitude. A large number of discharge experimental results show that, in the environment of pressure lower than 1 bar, with the increasing pressure, the average inception time lag of leader increases and the breakdown voltage of air gap also increases. In all the air pressure range, the increasing pressure leads to the decrease of leader propagation velocity, the larger leader diameter, and the lower expansion velocity of leader diameter. In a certain absolute humidity range, with the increasing absolute humidity, the inception time lag of streamer and leader increase and the breakdown voltage of air gap also becomes higher. Similar to air pressure, the higher absolute humidity gives rise to the increase of leader diameter and the decrease of leader propagation velocity and diameter expansion velocity.

Additional informations

Authors

C. ZHUANG, Y. GENG, Y. CUI, R. ZENG

Keywords

Air pressure, absolute humidity, leader discharge, leader velocity and diameter, breakdown voltage