The stroke defect of the electromagnet of high voltage circuit breaker is one of the main reasons which causes the circuit breaker not open. The stroke magnitude of the electromagnet cannot be directly measured by the feeler gauge in case of ‘on’ operation of circuit breaker. For this issue

a kind of non-contact measurement method of electromagnet stroke for circuit breaker is proposed. The picture of the electromagnet is obtained by the measurement system and the pixel size of the electromagnet matching gap is calculated by the use of K-Means algorithm in combination with the CLSD linear detection algorithm. In case of ‘on’ operation of circuit breaker

the calculation of the electromagnet stroke can not be performed by the reference calibration method inside the operating mechanism box of the circuit breaker. The calibration is performed by the vernier caliper in the experimental condition in combination with accurate positioning principle of laser sensor to obtain the pixel equivalent at a fixed distance

thereby calculating actual stoke of the electromagnet. The effectiveness of the method is verified by comparing the experimental measurement result at site and that of filler gauge.