Effect of humidity on positive corona discharge in a three electrode system

Abstract

Abstract The effect of humidity on the discharge development in a three electrode system (point-grid-plane) is studied. In dry air, the presence of a third electrode (grid) in a point to plane air gap plays an important role in controlling the potential gradient distribution in the air gap which in turn effects the gap dielectric strength and the discharge development. In humid air it is found that the appearance or disappearance of a certain corona mode as well as the transition from a corona mode to another are not only dependent on grid geometry, grid relative position, and grid potential, but are also dependent on air relative humidity. It is noticed that the corona inception voltage increases as the air relative humidity increases up to a certain limit after which the corona inception voltage begins to decrease with increasing air relative humidity. It is also found that the increase of air relative humidity favours the positive glow formation and affects its stability. A theoretical model is suggested to analyse the corona inception modes of discharge on a three electrode system in humid air. A comparison between theoretical and experimental findings is also presented.