RESEARCH OF SERVICE CONDITION IMPACTS ON CABLE POLYMER INSULATION

During last decades the intensive increase of using of polymer insulation materials in high voltage electric equipment such as cables, apparatus, surge arresters, transformers, and insulators takes place. With all wide well-known advantages the challenge of polymer insulation material deterioration and conditions of defects formation under influence of different service factors in full-scale are poorly studied. Water trees formation and its growing are concerned with humidity impact on the reduction of polymer insulation electric strength under non-uniform electric field. Water diffuses in polymer structure under electric field intensity and concentrates in volumes with high local heterogeneity, where water trees have a tendency to grow Despite unanimous agreement that the combination of water and electric field in polymer insulation affects its dielectric properties, there is no clear understanding of the water-tree aging process. Besides proposed deterioration physical models or registered service failure statistics have not been useful for calculation of insulation degradation level or remaining life. In paper the results of laboratory research of polymer material dielectric losses over high frequency range are represented. The dielectric losses measured by using of non-destructive dielectric response measurement techniques showed a good correlation with polymer insulation deterioration. On the basis of obtained results the mathematical model and rapid method of cable remaining life assessment is offered. Thermal deterioration of polymer cable insulation (especially polyethylene insulation) under service condition cannot be ruled out. Within the framework of the project the investigations of thermal deterioration of polyethylene insulation with using of method of X-ray structure analysis are carried out. During thermal deterioration investigations the correlations between dielectric losses and temperature load at different ageing time were defined.