Preventing Space Charge Injection and Accumulation Using Electrets Under Steep Voltage Pulses with Varying Duty Cycle

In medium-voltage direct current (MVDC) or highvoltage direct current (HVDC) systems, charge carriers inject into solid insulators, accumulate, and generate space charge. This phenomenon distorts electric fields and diminishes the effective thickness of dielectric materials, contributing to premature device failure. Electrets, comprising dielectric materials embedded with charges, independently generate internal electric fields, offering a potential solution. Our previous studies investigated how one could design, fabricate, and utilize electrets to neutralize locally concentrated high electric fields and mitigate space charge injection and accumulation under DC voltage. The effectiveness of electrets in mitigating space charge under square voltage stress has not been investigated. This study aims to experimentally demonstrate the efficacy of electrets in mitigating space charge injection and accumulation under unipolar square voltage stress, considering variations in the duty cycle of the applied voltage. To experimentally validate our study, we prepare a silicone rubber sample as the primary dielectric material. Electrets are fabricated by employing polyvinylidene fluoride (PVDF) through triode corona charging, and the embedded charges in the electrets are measured using an electrostatic voltmeter. Through space charge injection and accumulation experiments, we validate that electrets effectively mitigate these phenomena in dielectric materials under steep voltage pulses.