A closing latch in a spring type operating mechanism of a high voltage circuit breaker is engaged to maintain the circuit breaker in closing state.CT20 spring type operating mechanism is widely used in 126 kV circuit breakers.However

its closing latch unit occasionally fails to hold the closing state when the CT20 operating mechanism is used to operate a higher load circuit breaker.In order to explain the phenomena

a concept of reset time difference is proposed

which is the time difference between a big latch and a small latch of the closing latch unit approaching its stable state

respectively

in a closing operation of a high voltage circuit breaker.The reliability of the closing latch unit can be improved by increasing the reset time difference and some parameters that affect the reset time difference are analyzed by ADAMS software.The results show that the reset time difference increased with an increase of preloads of the big latch spring.A closing failure caused by the bounces of small latch can be solved by increasing preloads of the small latch spring and by decreasing stiffness of the small latch spring.The results provide information for an improvement of the closing latch unit of CT20 spring type operating mechanism.