Dynamic dielectric recovery property for vacuum circuit-breakers with double breaks

Based on the dynamic dielectric recovery process on the vacuum gaps in series, investigations were made on post-arc insulation state on double-break vacuum circuit breaker in high voltage power system. The Equivalent circuit of VCB with double breaks is set up for research on post arc dielectric recovery process. Depending on the rate of rise of the transient recovery voltage transient recovery voltage (TRV) and the arcing time in some cases the breakdown of one of the double-breaks does not lead to a failure of the whole arrangement. A sheath expansion model was set up for investigating the characteristics in the beginning stage of dielectric recovery process. As the voltage distribution between the two breaks is different on post-arc insulation state, the sheath-growing process in the two breaks is also different. The simulated data and experimental results show that the dynamic dielectric recovery property is strongly influenced by the sheath-growing process in the two breaks, which can be used for explaining the mechanism on the improvement of the breaking capacity for double-break units compared with single-break ones which have the same equivalent gap length. The test results are shown to confirm with the theoretical study of the suitable models proposed by the authors.