Non-destructive Diagnosis of Insulating Defects in polymeric Insulating Films for High Voltage Capacitors

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The purpose of this research work is to establish the non-destructive diagnostic method for the detection of insulating defects distributed in the polymeric electrical insulating films by using thermograph and to clarify their high field electrical conduction and breakdown characteristics in relation to the defects. The main results are as follows ;1. Local Joule heating appeared before the DC breakdown in polyethylene film and the breakdown occurred in this point probably due to themal breakdown process. Based on this result, non-destructive detection of insulating defects in insulating films becomes possible.2. Under AC voltage, local Joule heating hardly appeared, but it appeared after the heat treatment or oxidation of film, or acetophenone coating on electrode.3. Local Joule heating hardly appeared in hard polymeric films like polypropylene.4. Dielectric breakdown of polyethylene film occurs due to the composite positive feedback breakdown process of thermal breakdown and electromechanical breakdown at the defect points.