CFD analysis of the thermal interruption process of gases with low environmental impact in high voltage circuit breakers

Gases and gas mixtures with lower environmental impact are being investigated as possible alternatives to SF₆ as the switching medium in high voltage circuit breakers. One of the most important aspects of the investigation is the thermal interruption characteristic which depends on flow acceleration, and efficient cooling of the arc around current zero. In the present work, the influence of the gas properties on the thermal interruption capability is investigated using Computational Fluid Dynamics (CFD). A gas mixture of fluroketones with CO₂ as background gas is considered. The underlying thermal interruptions behavior of this gas mixture is compared with that of SF₆. The individual influence of the axial flow parameters namely pressure, velocity, Mach number and density on thermal interruption is studied. A thermal interruption proxy parameter is derived by combining the axial flow variables, which can better characterize the thermal interruption. The differences between the different gases using this proxy are presented. The design parameters influencing the pressure build-up and thermal interruption behavior are investigated and discussed.