Investigation on the Interruption Performance of a 252 kV Vacuum Circuit Breaker Under Close-in Fault Conditions

Circuit breakers are critical devices to ensure the safe and reliable operation of power systems. While SF6 gas, a strong greenhouse contributor, has been widely adopted in high-voltage circuit breakers worldwide, vacuum circuit breakers (VCB) have become the mainstream equipment in distribution systems up to 126 kV owing to their environmental advantages. To address the technological gap in vacuum interruption at higher voltage levels, this work investigates the interruption characteristics of a 252 kV VCB under close-in fault conditions. Experimental studies were carried out, and a vacuum arc model was fitted to characterize the arc behavior under such conditions, followed by a simulation analysis of the post-arc dielectric recovery process. Using an L90 close-in fault simulation platform, the research focuses on the contact separation behavior, arc extinction process, and the dynamic characteristics of current and voltage during the rapid rise stage of fault currents. Based on successfully interrupted test data, representative arcing times and the corresponding variations of arc voltage, current, and resistance were extracted. A fitted arc model of the 252 kV/50 kA VCB under close-in fault conditions was obtained. This model not only accurately captures the variation of sheath thickness during the post-arc dielectric recovery process, significantly improving simulation accuracy, but also provides an important empirical basis and theoretical reference for the subsequent rapid fitting and optimization of vacuum circuit breaker arc model parameters.