To understand the insulation defects of a circuit breaker switching coil and its internal defects

the structure

current

and causes of internal defects of the coil were analyzed. It was found that the local overheating or inter-turn short circuit

which happened as the working current passed through the internal defects of the coil

resulted in the insulation defects; faulty coil did not affect the performances of circuit breaker

but decreased its DC resistance

increased the coil current

and distorted the waveform.Disintegration test verified the analysis. In addition

effective countermeasures against the insulation defects of the switching coil of circuit breaker were proposed

and the pulse detection method for effectively exploring the defects in coils was introduced.