Estimation of cable life and service reliability

Abstract

This paper proposes a comprehensive method of statistical evaluation of cable life and service reliability, The method is based on Weibull statistics combined with a recently refined model of electrical aging which incorporates an initial dielectric strength into the conventional (Vnt=C) aging law, The method is essentially intended for extruded insulation cables but is applicable to other insulating systems which obey the Weibull statistics and assumed aging model, In addition to its main purpose, the method is suitable for selecting optimal material characteristics and safe voltage stress level for prerequisite cable life and reliability. It also helps to design and plan economically the statistical programs of accelerated aging tests. The paper includes the analysis of cable performance as a function of the stress hazard factor (the ratio of the applied stress and the initial dielectric strength), shape parameter of Weibull failure distributions and the material aging constants. The analyses are performed under the assumption that the material constants remain unchanged throughout the entire life of the insulation. A possible approach to life and reliability prediction for time dependent material parameters concludes the paper.