Improvement of vacuum circuit breaker model based on laboratory results

Driven by the concerns about the carbon footprint of distribution equipment and regulatory requirements, vacuum circuit breakers (VCBs) are replacing SF6 circuit breakers in Medium Voltage (MV) applications. Depending on network configurations, transient overvoltages can be induced by multiple restrikes of VCBs, underscoring the need for reliable VCB models to identify such harmful behaviours during the design stage of a network and mitigate them with protections like surge arresters or snubbers. In this paper, the methodology to supply an ElectroMagnetic Transient (EMT) VCB model with experimental data is detailed. In particular, the time-dependence of the VCB dielectric strength is deduced from dozens of restrike events, and the strong non-linearity of this curve is emphasized. The behaviour of this VCB model is then examined in an EMT test-case circuit and compared to voltage and current measurements observed in the same experimental circuit. Thanks to this method, the risk of high frequency overvoltages and overcurrents can be precisely assessed regarding the operational configuration and so the requirements of Enedis (the main French Distribution System Operator) specifications can be adjusted accordingly.