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High-voltage switchgear is a key control and protection unit in power systems. The reliable operation of the operating mechanism is essential for the reliable opening and closing of the switchgear. This is a vital guarantee for the safety and stability of the power systems. The spring operating mechanism is a commonly used actuator for circuit breakers at 12–252 kV. However, a reliability estimation method that is convenient, practical and accurate is still lacking. The aim of this paper is to explore a reliability estimation method based on a stress–strength interference reliability theory and a fatigue life theory. The changing rules of the reliability of the main axis, and the closing pawl and opening pawl in the spring operating mechanism during operations, are achieved. The accuracy of the calculated reliability based on theories of stress–strength interference and fatigue life is verified by adopting a test data statistical reliability model based on Weibull distribution. The results show that the reliability estimation method based on stress–strength interference and fatigue life theories has a high degree of confidence. The maximum tolerance is 0.024. The study would help in providing a useful reference for the optimization and durability estimation of a spring operating mechanism and its key components in high-voltage circuit breakers.

It is effective to open the bus-coupler circuit breaker in case of a short-circuit fault. A fast vacuum circuit breaker (FVCB) is an ideal bus-coupler circuit breaker due to its high velocity. The objective of this study was to develop and test a 252 kV/2500 A-40 kA multi-break bus-coupler FVCB. The 252 kV FVCB contained 12 FVCB units. Each phase consisted of four FVCB units connected in series. Each FVCB unit had an electromagnetic repulsion mechanism with an average opening velocity reaching 6.5 m/s. Test results showed the opening time was 1.11 ± 0.08 ms. The capacitance of the voltage grading capacitor of each break was determined to be 10 nF. The prototype 252 kV bus-coupler FVCB passed all partial test duties according to the IEC 62271-100: 2008 and IEC 62271-1: 2007 standards, which include an insulation test and a terminal fault test among others. A 252 kV/2500 A-40 kA multi-break bus-coupler FVCB can be used to quickly cut off a short-circuit fault and effectively limit a short-circuit current.

The prestrike phenomenon in vacuum circuit breakers (VCBs) is interesting but complicated. Previous studies mainly focus on the prestrike phenomenon in single-break VCBs. However, experimental work on prestrike characteristics of double-break VCBs cannot be found in literature. This paper aims to experimentally determine the probabilistic characteristics of prestrike gaps in a double-break VCB consisting of two commercial vacuum interrupters (VIs) in series under direct current (DC) voltages. As a benchmark, single-break prestrike gaps were measured by short-circuiting one of the VIs in a double break. The experimental results show that the 50% prestrike gap d50 of each VI in a double break, which is calculated with the complementary Weibull distribution, was significantly reduced by 25% to 72.7% compared with that in a single break. Due to the voltage-sharing effect in the double-break VCB, scatters in prestrike gaps of each VI in a double break was smaller than that in a single break. However, without the sharing-voltage effect, d50 of the low-voltage side in the double break was 65% higher than that of the same VI in the single break, which could be caused by the asynchronous property of mechanical actuators, the difference of the inherent prestrike characteristics of each VI and the unequal voltage-sharing ratio of VIs.