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Water Trees – Too Big to Fail?

October 5, 2011

Water Trees—Too Big to Fail?

Max dimension Sample A Sample B Sample C
Bow-tie trees 25% 36% 46%
Vented trees 18% 4% 0%
Voids no void geometry reported
Note: Values in percent are relative to insulation thickness.

Q:
We had three cable samples (tagged A, B, and C) sent out for testing from different areas. These areas are not those we are injecting this year. Each area has suffered multiple failures. I am attaching a confidential lab report (summarized within the table below) on the condition of the cables (presence of vented trees, voids and bow tie trees). We would like to have your opinion as to whether the injection process will be able to revive cables that have deterioration to this extent. Please send us any literature that you have, which can illustrate the extent of damaged cables and their successful rejuvenation.

A:
water trees - too big to failIn Star Wars Episode III, Revenge of the Sith, Obi-Wan was not discouraged by the presumed strength of a Sith Lord. It was easy for Obi-Wan to profess bravado, as he had slain a Sith Lord in a previous episode. Likewise, the Jedi Masters of Reliability at Novinium are not frightened of water trees – not even those that span 100% of the insulation thickness! Virtually all of the millions of meters of cable treated by Novinium Masters include very large water trees. Even previous generations of technology developed by Novinium founders have successfully rejuvenated cables with monstrous, Sith-like water trees.Consider the graph nearby, which compiles before-and-after AC breakdown values as a function of water tree length from several sources. To provide context, a construct of KEMA’s Fred Steennis is included. Fred is the world’s foremost authority on water treeing and a friend of mine. The curve labeled, “Steennis Model,” shows the relationship between the largest water tree length identified in a cable and the AC breakdown (ACBD) strength in kV per millimeter of insulation thickness. With a great deal of field data, Dr. Steennis was also able to determine that a “Good” box is delineated at its bottom at 16 kV/mm. Of the dozens of cables removed from service in the Netherlands utilized to create this curve, none with over 16 kV/mm of ACBD had ever failed in service.  Below 16 kV/mm there were service reliability issues. Six before-treatment and after-treatment examples with trees ranging from 25% to 100% of the insulation thickness are provided from circuit owners in North America and Europe. In all cases treatment is able to raise the AC breakdown values above 16kV/mm, generally approaching the anticipated AC breakdown values expected of a new polyethylene cable, about 40 kV/mm. The newest Novinium technology can accomplish this feat in as little as a week. Here are sources for the data in that figure.

Reference Citation
Steennis work Steennis et al, “Water Treeing in Service Aged Cables, Experience and Evaluation Procedure,” IEEE Transactions on Power Delivery, Vol. 5, No.1, January 1990.
CPS Energy (San Antonio, TX) Mokry, Chatterton, Carter, Sibbald, Clemmer, Bertini & George, “Cable Fault Prevention Using Dielectric Enhancement Technology,” Jicable, June 1995. Republished in REE Spécial Câbles.
Essent (EGD/Edon, Netherlands)
OG&E (Oklahoma Gas & Electric)
Virginia Power (VEPCO)
Florida Power & Light (FPL)
Cable Tech. Labs (CTL, New Jersey) Bertini, “New Developments in Solid Dielectric Life Extension Technology”, IEEE International Symposium on Electrical Insulation (ISEI), September 2004. Click here to view.

No matter the size of your vented or bow-tie water trees, Novinium’s Jedi Masters of Reliability will take them on and defeat them. Preserve your capital and avoid the seductive dark side—expensive cable replacement.