End Of Life Of Xlpe Dielectric…Appraising Condition And Prioritising Replacement

Input from papers by Dr John Densley (IEEE Canada), Paul Caronia (DOW Chemical), Warren Batchelor (Unison Networks NZ), Trevor Lord (LORD Consulting), David Griffiths (Olex Cables), Nick Chandler (Chandler Consulting), and Dr Lee Renforth (IPEC Engineering UK):

-    An ODV of 45 years for XLPE cable effectively assumes 1970’s XLPE cable is as good as today’s product which, judging by reported material and virtually all published literature, was observed to be clearly flawed logic!!
-    “Have you got a cable replacement policy?” was a question raised. If so, is it a managed one based upon condition or reactive one based on age or failure rate? A pro-active policy was advocated and a more formal model for such an approach proposed and reviewed.
-    A correctly-conceived cable assessment and replacement policy was also reported as assisting in managing future funding forecasts, planned reconfiguration, and avoiding the real risk of a domino effect from failures
-    Partial Discharge, especially in joints and terminations, was reported as a major cause of premature failures and reliability issues over the life of an XLPE cable and can occur from start-up. It can give reliable warning of pending failure in energised cables. Continuous PD monitoring units are now available.
-    Technology to determine PD condition is now on hand with levels of sophistication, ease of use, and pricing per test at levels never before seen.
-    Water Treeing is one of the major determinants affecting XLPE dielectric condition in ‘aged’ non-TRXLPE cable
-    Water Treeing is the main cause of end of life and can destroy the cable in as little as 7 years in such cable
-    VLF Tan Delta testing is the main internationally-accepted means to determine and quantify water treeing, the test taking 5 minutes and recommended to be used prior to VLF testing. IEEE have researched the matter fully and published VLF Tan Delta testing guideline material.
-    Unison reported that 66% of cables that ultimately failed on VLF over pressure testing had shown poor VLF tan delta prior. Unison’s findings confirm the validity of the technique but they are currently the only company in NZ practicing this approach!!
-    A call for the NZ Industry to adopt an improved ‘best practice’ approach using both PD and VLF Tan Delta techniques was made by several presenters.

pic-6 pic-7
Water Treeing in extruded insulation Unison NZ conducting VLF Tan Delta testing, recommended by them as the main tool for prioritising cable replacement in aged XLPE. A quick test, it requires a modest outlay of just NZD 40,000 +GST.
An example of the field-ready PD test equipment now offered for exceptionally low-cost PD surveys on aged XLPE cable (& switch gear). Outlay: NZD 18,300 +GST and just 1 hour of training needed for fitter staff!!

Contact us for fuller advice on managing your XLPE cables and prioritising end of life replacement.