The surface charge of Al2O3 ceramic insulator under nanosecond pulse voltage in high vacuum: characteristics and its impact on surface electric field

Abstract

The electrical strength of insulator in vacuum is much lower than either the insulator itself or the vacuum gap in the same dimension, and one of the considerable factors that could affect the electric field or even the surface flashover is the surface charge accumulation. In order to capture the surface charge characteristics and its impacting mechanism on electric field of ceramic insulator under nanosecond voltage in vacuum, this paper employed electrostatic capacitive probe to develop a surface charge measurement system. The accumulating and dissipating characteristics of surface charge on four Al2O3 ceramic insulators with different manufacturing conditions were captured, indicating that, (1) the surface charge mainly accumulates near the anode, but there presents various distribution patterns of different samples; (2) the charge density of different samples also shows different increasing trend with the voltage application counts increasing, and the maximum difference could reach 78.07%; (3) within 1 h after the voltage cutting off, the maximum density of dissipated surface charge on all samples is less than 7.0%, ensuring the reliability and effectiveness of experimental results. The surface micro-morphology and surface traps characteristic take the joint actions to make the explanations for the surface charge accumulation and migration mechanisms. Finally, based on surface charge measurement results and field simulation results, the quantitative impact of surface charge on surface electric field were proposed in this paper, aiming at providing meaningful references for the insulation design.