A Method for Cable Failure Analysis Based on Ageing Model and with Consideration of Daily Temperatures

The physics- based electro-thermal ageing model has been widely used for analysis of cable failures and for evaluation of insulation status for single cable circuits. However, previously published approaches only reflect increased failure probability on an annual basis which cannot be used to explain the phenomenon that higher number of cable failures have been observed during summer time by Scottish Power Energy Networks (SPEN). Despite the insulation degradation accumulated annually, higher daily temperature during summer seasons resulted in extra stochastic stress applied on cable insulation and led to increasing cable failure probability. During summer seasons, the majority of cable failures occurred when daily temperature was higher than 10 °C. This paper aims to improve the electro-thermal model to evaluate remnant insulation strength and failure probability with consideration of stochastic stress due to higher daily temperature. Failure occurs when the stochastic stress overwhelms the remnant insulation strength. With the improved model, failure probability can reflect higher number of failures during the summer season.