Method for Estimation of the Remaining Lifetime of 6.6 KV XLPE Cables After Their First Failure in Service

This paper describes a new method for estimation of the remaining useful life of a power cable which has failed and has then been repaired. The estimation is based on our observation of the lengths of vented and bow-tie water trees in a section of cable that was removed during repair, calculation of the rate at which these trees grew during the period of service, the level of AC or impulse breakdown strength at which failure will occur again, and the assumption that water trees grow in the same manner before failure and after repair. A new concept of "maximum tree length" is introduced as a numerical parameter which can be used to characterize the relation between the length and number of trees in calculating the growth rate. The maximum tree length l depends on both the length and conditions of service before failure occurred.