An Experimental Circuit Breaker for Benchmarking the Intrinsic Interruption Performance of SF6 Alternative Gas Mixtures

Currently, there is significant effort worldwide in the research and development of SF6-free high-voltage circuit breakers, both in academia and industry. One of the most important switching capabilities is thermal current interruption, a process that, in modern self-blast breakers, strongly depends on the coupled effects of nozzle geometry, nozzle ablation, backheating, pressure build-up and gas outflow, as well as contact and puffer cylinder motion actuated through the drive. Previously published investigations on the thermal interruption performance of novel switching gases have used such designs, however, due to the many coupled processes, it is not possible to control the interruption conditions in order to make a full and comparative evaluation of different SF6 alternative gas mixtures. The aim of the present contribution is to present an experimental circuit breaker tailored for use in basic experiments that allow for an unbiased comparison of properties of alternative gas mixtures relevant for current interruption. The breaker is based on a novel puffer design with an overpressure relief valve that allows the contact stroke and blow pressure to be predicted, controlled and adjusted over a wide parameter range at current zero. This contribution lists the requirements for such an experimental circuit breaker and focuses on its design realization. Experimental validation is given that this device can be used in benchmarking the interruption characteristics of SF6 alternatives. Systematic comparison of the thermal interruption performance of SF6 alternatives and investigations of the processes around current zero will be reported in other publications.