Statistical treatment of breakdown tests for extruded insulation

If identical extruded HV power cables are stressed under identical conditions, they will not breakdown after the same period of time. Consequently it is not possible to predict the life of cable insulation even in the unlikely event of knowing the exact service conditions and knowing the life of a similar cable under similar conditions. It is therefore necessary to consider the lifetimes of cables as following a statistical distribution. This paper considers the statistical nature of breakdown and how applied voltage may influence the lifetime. Some examples are given, but unfortunately very little conclusive data have been published for high voltage cables to date