Real World I – High K
In my last post of 2011 one of my local fans, Wondering in Western Washington, questioned the veracity of the claims made by UTILX® in a document titled, “Life Extension Estimate for UtilX® CableCURE® Rejuvenation Fluid.” That document includes 17 pages and many, many claims. In this first of a series of posts, I examine the following set of claims from page 3:
Once the CableCURE® molecule reaches those sites it performs two important functions. First, it chemically combines with the water, desiccating the water tree site. Second, it polymerizes; the polymeric chain that forms continues to grow until its chain length traps it inside of the water tree structure. Once trapped inside of the cables insulation, it serves as a “high K" style stress gradient reducing the electrical stress amplification that occurs at the tips of the water tree “branches". This two part functionality arrests the growth of water trees in aging cable.
I added highlighting to focus on the words and phrases of the claims that could create confusion; I left all puctuation and grammer errors untouched. The first two words I highlighted could be characterized as quibbles, but I endeavor to be precise in my language. I am sure the author will appreciate my clarifications, since these claims taken together with others are held out as “irrefutable proof” of CableCURE efficacy. The third highlighted “high K” claim will receive the majority of my attention today.
The CableCURE molecule to which the author refers is phenylmethyldimethoxysilane or PMDMS for short. The chemical reaction of PMDMS with water is well understood. On average each PDDMS molecule consumes about one water molecule. The effect is real, but the implication of the claim is that this desiccation-by-reaction is one of PMDMS’s two important functions. It is not. The reaction with water is a necessary precursor to a subsequent condensation reaction. In the next sentence the author refers to this second reaction as polymerization.* Chemical desiccation is not important because the phenomenon is fleeting. Consider the data reported by another UTILX employee in “The Importance of Diffusion and Water Scavenging in Dielectric Enhancement of Aged Medium Voltage Underground Cables” at the IEEE PES T&D meeting in Chicago, 1994. Figure 4 and the accompanying text indicate that the water reactive capacity of PMDMS is exhausted at between 54 and 67 days for a 1/0 conductor at 60°C. At lower temperatures the time to exhaustion might be longer, even on the order of a year or even two. When one is talking about decade-long life extension, a couple of months or a couple of years is not of critical importance. None-the-less, PMDMS does help keep the insulation dry for many, many years, but not by the mechanism suggested by the author. Instead, the mechanism is preferential wetting, which is well described in U.S. Patent 7,976,747 held by Novinium and in the paper “Advances in Chemical Rejuvenation of Submarine Cables” available here. The reason the distinction is important is that only Novinium® brand Ultrinium™ 73X fluids include components with preferential wetting properties superior to PMDMS. Reducing the amount of water present in the insulation is indeed important, but not all rejuvenation fluids perform the same in water reduction efficacy.
The word “trap” is too absolute for this frog. Trap implies eternity and it just isn’t so. In a December 29, 2010 post, “Chain Entanglement,” I explain how the larger oligomers substantially retard the exudation of the rejuvenation fluid, but it is not trapped. As shown in the figure nearby, improvements in rejuvenation molecules patented by Novinium (U.S. patent 7,658,808 and others pending) are designed to stick around in the insulation longer than PMDMS.
There is no agreed-upon definition for High K, when applied to stress grading in power applications. At 20°C and 60Hz, the dielectric constant or “K” of unfilled polyethylene is about 2.3 and EPR insulation varies from about 2.7 to 2.8 depending upon the specific compound. (See Bartnikas & Srivastava, Power and Communication Cables, IEEE 2000.) The dielectric constant for PMDMS is 3.2. The dielectric constant of PMDMS is indeed higher than PE and EPR insulation, but using the word “high” is a bit of a stretch. High K materials are quite often used in shrink-to-fit splices and terminations. For example, 3M’s data sheet for its Quick Term II Silicone Rubber Termination Kit states: “The High-K material has a dielectric constant of about 25.” Pure water has a K of 78. Cyanobutylmethyldialkoxysilane or CBMDAS for short, a patented component of Novinium® brand Ultrinium™ 73X fluids, has a K much greater than that of water. 3M’s stress control material, water, and CBMDAS are “real life” High-K materials. I have arranged these six materials in a table nearby for easy reference.
I object to the statement proffered by the author for two reasons …
1. It is an assertion without proof. If the author believes that the mechanism he claims is significant with a K of just 3.3, he should provide a calculation or measurement as substantiation.
2. The PMDMS is replacing water, which has a much higher dielectric constant. How could that conceivably provide stress grading? CBMDAS on the other hand, enjoys a K greater than the water it replaces.
The author of “Life Extension Estimate for UtilX® CableCURE® Rejuvenation Fluid” is not a master of the facts. While CableCURE fluid does dry the cable and extend its life, the explanation of why this is so lacks foundation. Stress grading at the microscopic scale is possible with materials that have dielectric constants greater than the water that they replace. One example of such a material is available only from Novinium and is protected by a U.S. Patent, other pending patents, and their foreign equivalents. While this frog cannot be sure what the author was thinking when he made his claim, I can provide a common-sense recommendation: Do not rely on secret documents that have not been peer reviewed … especially if they include assertions without proof.
Always basking in transparency,
Thermonuclear Bull Frog
*The correct terminology is oligomerization, but I will let that slide.