Effects of DC Component in Asymmetric Fault Current on the Thermal Recovery Characteristics of an SF sub(6) Autoexpansion Circuit Breaker

A 2-D magnetohydrodynamic arc model is used to study the thermal recovery processes with long and short arc durations in an autoexpansion circuit breaker where a significant dc component in the fault current exists. The influence of the dc component on the pressure built-up in the expansion volume was first investigated and the thermal recovery characteristics compared with cases where asymmetry of the fault current is negligible. Results show that, in comparison with the cases of symmetrical fault current, pressurization in the expansion volume is largely determined by the arc energy in the second half cycle of fault current, which is significantly influenced by the dc component. The dc component affects evidently the arc temperature at the current zero point and leads to a reduction in the critical rate of rise of recovery voltage.