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

本研究工作的目的是建立一种利用热像仪检测聚合物电绝缘膜中绝缘缺陷的无损诊断方法，并阐明与缺陷相关的高场导电和击穿特性。主要研究结果如下：1.聚乙烯薄膜在直流击穿前出现了局部焦耳热现象，击穿发生在这一点上，可能是热击穿的结果。基于这一结果，绝缘膜中绝缘缺陷的无损检测成为可能.在交流电压下，局部焦耳热几乎不出现，但在热处理或膜的氧化后，或苯乙酮涂覆在电极上后，局部焦耳热会出现.在聚丙烯等硬聚合物薄膜中几乎不出现局部焦耳热.聚乙烯薄膜的介电击穿是由缺陷点处的热击穿和机电击穿的复合正反馈击穿过程引起的。

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.