The pre-breakdown phenomenon of double-break vacuum circuit breaker (VCBs) usually shows non-simultaneous breakdown of each break due to the influence of dispersion of closing operation

different contact surface conditions and dispersion of vacuum gap breakdown voltage. Nowadays

there is still a lack of research related to the pre-breakdown characteristics of non-synchronous making operation of series vacuum gap. The objective in this paper is to experimentally study the characteristic of pre-breakdown clearance and pre-breakdown voltage distribution of the double-break vacuum circuit breaker in asynchronous making operation. In the experiment

two commercial vacuum interrupters (VIs) in series connection are taken as the study object and such four sets of experimental conditions for making operation as synchronous making operation of double breaks

making operation with low voltage side 1 ms faster than the high voltage side

making operation with high voltage 0.5 ms faster than the voltage voltage side

making operation with high voltage side 0.2 ms faster than the low voltage side are set to simulate asynchronous making operation of double-break vacuum circuit breaker. The Weibull probability distribution of 50% pre-breakdown clearance

d

50

and the 50% pre-breakdown voltage

U

50

of each break is achieved by the experiment. The study results show that in case of making operation at high the break of high voltage side 0.2 ms faster than that of low voltage side

the dispersion of the pre-breakdown clearance of the double-break is smaller than in the synchronous making due to voltage division effect of the double-break vacuum circuit breaker. The asynchronous making operation of the double-break vacuum circuit breaker can change the voltage division ratio of the double-break vacuum circuit breaker.