During long-term use of a circuit breaker

the over-travel will change due to contact wear

screw loosening

etc. which makes the determination of circuit breaker’s opening/closing instant difficult. To obtain an accurate judgment method of the opening and closing instants in the case of over-travel variation

this research took a 12 kV AC medium-voltage vacuum circuit breaker as the object of study to build an off-line test platform for monitoring the circuit breaker’s mechanical condition. Firstly

after simulation of different over-travels

the transposition signal of contactor and the vibration signal in opening/closing process of the circuit breaker were collected synchronously.Then

the short-time energy method was used to process the vibration signal and analyze the corresponding relationship between the opening and closing instants extracted from the transposition signal and the characteristic quantities extracted from the vibration signal. The vibration signal is used to replace the transposition signal so as to exactly determine the opening and closing instants and accurately calculate the opening and closing time through extraction of the vibration signal in the opening and closing process of the circuit breaker. The result shows that under variation of the over-travel

this method can reduce the judgment error of the opening and closing instants to 0.5 ms

which means that it improves the accuracy of the monitoring results.This research may provide a reliable and accurate method for on-line monitoring of mechanical condition of circuit breakers.