The Assessment of Contact Conditions in Vacuum Circuit Breakers using Field Emission Current Measurement

– The performance of vacuum circuit breakers (VCBs) in interrupting and protecting an electric power system heavily relies on the contact conditions; hence, the assessment of these conditions is paramount. The field emission current has emerged as a highly effective parameter for both qualitative and quantitative investigations of contact conditions. Traditionally, the measurement method utilizing the field emission current to determine contact conditions was conducted under AC voltage, necessitating the disassembly of the VCB, thereby limiting its practical application. The aim of this study is to introduce a novel measurement technique for assessing contact conditions within a VCB during the closing operation under DC voltage, utilizing the field emission current. This novel method eliminates the need for VCB disassembly and streamlines the processing of experimental data. Subsequently, this measurement method is employed to explore contact conditions during capacitive switching. The findings reveal that the field enhancement factor <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\beta$</tex> of the contact surface exhibits oscillatory behavior during the capacitive experiment, confirming the conditioning and deconditioning effects of the inrush current on contact surfaces.