Surface Potential Dynamics of Polyimide Under DC Corona Based on Noninvasive Measurement

Abstract

To explore the surface charge behavior of polyimide films under corona discharge, the surface potential at both high-voltage (HV) stage and short-circuit (SC) stage is measured by a noninvasive method. DC HVs with different magnitudes, polarities, and durations are applied to a needle electrode to generate corona discharge. The surface potential without corona discharge exhibits a homopolar pulse at the HV stage and a heteropolar pulse at the SC stage because of interfacial polarization and depolarization. This article proposes a three-region model (including corona region, homopolar-charge region, and sample surface region) to explain the surface potential evolution with corona discharge. Surface potential under corona discharge shows a large fluctuation followed by decay with oscillation during the HV stage. The combined effect of interfacial depolarization and surface charge leakage explains the “backtracking” phenomenon at the SC stage. From the comparison under different polarities, it is found that negative corona produces more charge deposition than the positive case, and the leakage rate of negative charge is faster than that of positive charge. Moreover, both a lower applied voltage and a longer duration lead to a smaller amount of residual surface charge and a more obvious “backtracking” phenomenon. It is expected that this article will help to understand the surface charge behavior under dc corona in future studies.