In this paper

a new method is presented that the determination of dynamic static contact opening/closing instant and break states

during circuit breaker off-line/on-line operation

an on-line monitoring method which measurement the pull and pressure force of the insulated tension pole by force sensor and compute the force sudden change time by force time curve. With this method

an on-line monitoring mechanical characteristics device has been designed and installed in a circuit breaker. The circuit breaker has passed short-circuit breaking and making capacity test as well as mechanical characteristics comparison test in National Center for Quality Supervision and Inspection（Xi’an test station）

time error of closing/opening time between monitoring data and laboratory test results is less than1 ms. Effective application of this method laid the foundation for control of selection phase-controlled

on-line monitoring for mechanical characteristics and electric life in the intelligent circuit breaker.