Investigation of the ageing process in polymeric insulators by using improved Weibull statistics

Surface tracking on organic solid insulators is one of the main reasons for failure in high voltage (HV) systems. Due to various factors, such as humidity, pollution, ice load, increase in local voltage, etc., it is hard to make an estimation about the life of an insulator. For many years Weibull statistics have been widely used and accepted as a successful mathematical method to predict the remaining lifetime of an insulating material. The basic reliability function R(t) = e^(-λtm), where ´λ´ is the scale and ´m´ is the shape parameter, can perform well for certain conditions, however it might be insufficient in lifetime prediction in multi-variable conditions. In this research several tests have been performed according to IEC 587 Inclined Plane Test method to investigate the breakdown times of polymeric insulation materials under various external conditions generated artificially in laboratory. These factors seemed to reduce the lifetime of insulating materials up to 50-70 percent. A model based on Weibull statistics has been proposed for estimating the breakdown time of polymeric insulation material. By using appropriate parameters this improved model can make successful estimates within a reasonable accuracy in varying external conditions such as tensile stress or increased surface hydrophobicity, etc.