Economic evaluation of cable replacement considering annual failure probability

Usually, the lifetime of electric power apparatus is assumed as the period with low failure probability. In this paper the power cable with water-tree degradation, for which available data are relatively rich; was studied as an example to discuss the economically optimum replacement time of the power apparatuses. From the accelerating-degradation test, the growth rate of maximum water-tree length was calculated. Then the annual failure probability of the cable was computed by using the Weibull distribution plot of breakdown voltage for the cables with different maximum water-tree length. The total cost is a function of the replacement time or the estimated lifetime and the ratio of the average loss by one failure to the replacement expense. The optimized replacement time which corresponded to the minimum total cost was evaluated under different practical conditions.