Correlation of accelerated ageing phenomena and long-term cable performance

Utilities, cable makers and industry experts generally agree that the results of medium voltage cable qualification testing are a good indication of ultimate cable performance and expected lifetime. Here we focus on the development of a new enhanced cable insulation material for distribution cables. While qualification tests can differentiate poor performing materials from those with superior performance, it will be illustrated that correlating such qualification data to life expectancy is much more complex. The data presented show that the enhancements observed during material development in water treeing behavior and breakdown strength measured in the short-term 30 day laboratory tests led to a moderate 15% improvement in qualification results. However, significantly larger increases in the time-to-failure and characteristic life time of 400% for cables in the ACLT test were recorded. It would be expected that similar enhancements would be achieved for cables under service conditions in the field.