Thermal current interruption in CO₂-based mixtures: I. Evaluating parameter dependence

A comprehensive experimental investigation into the switching behavior of CO2-based SF6 alternative gas mixtures under short-line fault-like conditions has been performed at ETH Zurich. An initial investigation into mixture composition sensitivity showed similar thermal interruption performance among all CO2-based mixtures, but also revealed that mixtures without fluorinated additives may suffer hot-dielectric failures that reduce their overall interruption limit. The first part of the study presented here is focused on relating the results of experimental investigations into the parameter dependence of current interruption in CO2-based mixtures, particularly the dependencies on circuit breaker opening position and blow pressure at current zero. A detailed examination of these relationships was made possible by the high level of control, reproducibility, and number of tests afforded by an experimental puffer circuit breaker. A statistical analysis of a large dataset of interruption tests performed with this device was also used characterize the probability distribution of thermal interruption test outcomes and establish measurement uncertainties. The main goal and novelty of this contribution is thus to clearly establish the distribution function of thermal interruption tests as well as the contact gap dependence and blow pressure scaling laws in the CO2-based SF6 alternatives. Part II will go on to examine how modifications to the flow conditions through nozzle shape parameters can influence the interruption performance, and will more closely examine the findings of the study with the aid of a 1-D arc model.