Investigation on dielectric breakdown behavior of thermally aged cross-linked polyethylene cable insulation

With the rapid development of industry and the increasing demand of power supply, the rated voltage class and current-carrying capacity of power cables become higher and higher, causing the severer service and testing conditions for high voltage (HV) power cables. Therefore, the requirement of the quality of cable insulating materials also becomes increasingly higher. The dielectric breakdown strength is one of the most important indices characterizing the quality and present status of insulating materials, and insulating materials and systems undergo dielectric breakdown tests during development and service. A lot of research results on the dielectric breakdown characterization of polyethylene (PE) and cross-linked polyethylene (XLPE) have been reported up to now, however, few systematic investigations about the dielectric breakdown behaviors of the thermally-aged XLPE cable insulation have been reported in details. Generally, the behaviors of dielectric breakdown for HV insulating materials and structures have been known to obey some statistical distributions, including the Weibull statistical distribution. The changes of the parameters characterizing the Weibull statistical distribution, e.g. the scale and shape parameters may be closely related with those of the physical and chemical properties of the insulating materials considered. This paper aims to investigate the behaviors of the changes of the Weibull statistical parameters for XLPE cable specimens with the different degrees of thermal aging and to elucidate their mechanisms. The investigation results show that the dielectric breakdown characteristics of thermally aged XLPE cable insulating materials also fit well with the Weibull statistical distribution and the changes of their Weibull statistical parameters are very sensitive to the degree of thermal aging, which can be effectively used for the diagnosis of PE or XLPE cable insulation and the analysis of its degradation mechanisms.