Characteristics Study Of Electrical Aging In Polymer Insulation Under Cryogenic Condition

Cryogenic insulation has been one of the key technologies of superconductive application in field of electrical equipment. Polymer insulation has been widely used at room temperature because of its better dielectric and mechanical performance, but the study of polymer application under cryogenic conditions is much scarce. So the paper grounds on the degradation and aging characteristics of room temperature and focuses on the polymethyl methacrylate (PMMA) and ultra-high molecular weight polyethylene (UHMW-PE). The paper study well the degradation and aging process of polymer insulation under cryogenic condition. The results can be the basis of the evaluation criterion and test mode under cryogenic conditions.The cryogenic degradation and aging test system has been constructed, of which detection circuit grounds on the impulse current test method. The test system has wide detection frequency band as well as excellent sensitivity. Various partial discharge (PD) characteristics and particular test data of degradation and aging process have been afforded by the detection system. The test method has been also developed in the paper.In order to study well the relationship between PD characteristics and electrical tree, the paper study the influence of different size and shape of void on the PD characteristics. The results indicate that PD behaviors can be changed with the increase of defects'depth and maximum PD magnitude goes up with the depth increase. According with the degradation trace, the paper has studied the influence of thermal, chemical and mechanical effects on the electrical tree development.The relations between PD characteristics and electrical trees development have been studied through the contrast with the results on room temperature conditions. The paper focuses on the influence of cryogenic-room circle factors, mechanical stress factors and time factors on the degradation and aging process. The results indicate that the relation between PD characteristics and electrical trees are stable. The strong stress can accelerates the growth speed of electrical tree. The PD behaviors will change from electrical trees'PD to dimension fixed voids'PD with time goes on.The paper also studies the influence of aggregation structure and crystallization state on the degradation and aging process by Differential Scaning Calarmeutry (DSC) and X-ray diffraction tests. The results show that the aggregation structure has less influence on the electrical trees development, which compared with the results at room temperature. The crystallization state can influence the aging process badly. Electrical trees'growth points to the crystallization zone and the polymer with small dimension crystallization zone can form bunch trees inside.