Occasionally closing operation failures occurred when a spring type operating mechanism was used to operate a high voltage circuit breaker with higher loads. This kind of failures is a high risk for circuit breakers. The objective of this paper is to propose a concept of reset time difference of a trip-open unit and to improve the reliability of closing operation of a high voltage circuit breaker with a spring type operating mechanism based on the reset time difference. In a spring type operating mechanism, there is a big latch and a small latch in a trip-open latch unit. In a close operation of a high voltage circuit breaker driven by a spring type operating mechanism, there is a time lag between the big latch and the small latch when they reach their final latched positions. And we definite the time lag as the reset time difference (TR). The experimental results showed that the reliability of closing operation can be guaranteed with TR was higher than 10ms. And TR increased with an increase of a preload of the big latch spring. And the bounces of the small latch were the most significant factor to cause a closing operation failure. An improvement from the point of view of time reset difference (TR) enhanced the reliability of closing operation of a high voltage circuit breaker.
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