As traditional type tests could not detect the state of arcing contact of an SF6 circuit breaker

this paper proposes a method to diagnose the state of the arcing contact based on the dynamic contact resistance curve between the moving and fixed contacts. The current source of synthetic test circuits is used to conduct electrical erosion experiment on the tested circuit breaker

where the rated short circuit current（40 k A RMS） is cut off from zero to 22 times. The dynamic contact resistance curve is measured after each electrical erosion experiment

and the correlation coefficient between the initial and measured curves is taken as the characteristic parameter for diagnosing the state of arcing contact. Obvious change is found on the correlation coefficient after cutting off the current for 15 times. This phenomenon illustrates the service limit of the arcing contact. Experimental results show that the dynamic contact resistance curve can perfectly reflect erosion status of the arcing contact

and it is an effective way to state diagnosis of the arcing contact.