Optical characterization of actively cooled switching arcs in SF₆ alternatives

Abstract A detailed study of the evolution of transient arc properties in SF 6 alternative gas mixtures was carried out on an experimental puffer circuit breaker. Thermal interruption tests were performed in several CO 2 -based mixtures under short-line fault-like current and voltage stresses, with the test device providing a similar arc environment and interruption performance to a commercial circuit breaker. The time evolution of arc properties including the radius, temperature, and electron density were investigated using high-speed imaging and optical emission spectroscopy techniques. These results were compared with simulation results from a simple 1-D, two-zone arc model. Spatially resolved measurements of the arc were obtained in the critical interruption regions of the nozzle, including the first reported 2D measurements of the temperature distribution during the interruption process in CO 2 . These measurements revealed a faster temperature decay in the nozzle throat, indicative of stronger cooling in this region compared to the upstream stagnation zone. Comparisons between the behavior of SF 6 and its alternatives largely agreed with the model predictions, with lower temperatures and earlier temperature decay observed in SF 6 , followed by CO 2 -based mixtures, while air exhibited the highest temperatures and latest onset of temperature decay. No significant influence of oxygen content was observed on the maximum arc temperature of CO 2 / O 2 mixtures at currents above 500 A, where values ranging from 20 kK to 25 kK were typically observed.