Failure Causes II

In yesterday’s post, “Failure Causes I,” I provided a partial answer to an inquiry from Colorado Querier. Colorado sought to understand if rejuvenation technology was appropriate for the “many types of aging factors” from which his firm’s circuits might suffer. In yesterday’s post we dealt with circuit failures caused by connected components, rather than the cable itself. Today we will focus on cable failures.  First a disclaimer – it is often difficult to determine with 100% certainty the cause of a cable failure in field conditions. A cable failure is a destructive event that usually vaporizes its own root cause. Those who analyze field failures can examine the cable near its fault for neighboring defects. If a defect or defects are found, the examiner may infer without certainty that a similar defect may have been the root cause of the actual fault. If no substantial defects are found the root cause will surely remain unknowable.

I emphasized “substantial” in the last sentence because at a small enough scale there are always defects. Water trees grow in all medium voltage solid dielectric cables exposed to moist conditions. Unless you have hermetically sealed metal sheaths, those would be your cables! Water treeing is an oxidative process, but even where there are no water trees, oxidation of the polymer occurs, because oxygen and other oxidizing agents are ubiquitous. Free radicals facilitate oxidation and are common in nature. Cosmic radiation, radioactive decay, and other natural processes spawn free radicals around the clock. On top of those chemical processes there are mechanical strains placed on the cable by thermal cycling driven by load cycling.  Such thermal cycling creates micro-voids in the middle radius of the insulation driven by the “Molecular Thermodynamics of Water in Direct-Buried Power Cables.” Click here to view the paper by the same name from IEEE Electrical Insulation Magazine (Nov/Dec 2006). The collection of voids formed this way are referred to as a halo.  I provide an illustration of a halo and water tree nearby.

What are the primary causes of failure and how is each addressed or not addressed by rejuvenation?

In the frogograph nearby, I show you a subset of field reliability data (Editors note: I have come to call this kind of data – “real, real world!”) gathered by Dr. Steennis of KEMA. The simple logarithmic equation explains 78% of the relationship between maximum water tree length, expressed as a percentage of the insulation thickness and reliability expressed as AC breakdown strength.  AC breakdown strength is not a perfect surrogate for cable reliability, but it’s a pretty good one!  Lightning bolts appear next to each cable sample that failed in service. Water tree length is the single best predictor of reliability. In the same work, Dr. Steennis and his colleagues demonstrated that the laboratory failure of the field aged cables always occurred at the longest water tree, just as a chain fails at its weakest link.

Well over three-quarters of solid dielectric cable failures are caused by water trees. Rejuvenation technology was originally designed to address water tree degradation specifically. In fact, rejuvenation has a proven track record of treating the biggest and ugliest water trees on the planet.  Click here, to check out my October 5, 2011 post, “Water Trees – Too Big to Fail?” In my third post of this series we will examine the other less important root causes of cable failure and consider whether or not those root causes can or cannot be addressed by the application of rejuvenation technology.

Master of Reliability,

T. Bull Frog

Failure Causes I

Dear Beautiful Bull Frog-

I wonder if you have any information I could use to help address a concern I have heard in my company.  That concern is that a 30 to 40 year old cable may have accumulated degradation due to many types of aging factors. Cable injection may not substantially address these factors and injection may not provide a very great increase of life extension for a very old cable.

Colorado Querier

Thank you for the inquiry Colorado. That is actually a great inquiry, because it will take me more than a single post to answer! The first question we have to address is:  Which of the two categories of failures plague your solid dielectric circuits?  In the figure nearby I ponder this question, because only you can know? At Jicable 2007, the International Conference on Insulated Power Cables, Nigel Hampton of NEETRAC (National Electric Energy Testing Research and Applications Center) provided some survey data from their circuit owner members in a paper titled, “Validating cable diagnostic tests.”  Perceived failure experience of NEETRAC member companies suggested that on average, 55% of the failures in the population are cable failures, 39% are accessory failures, and 6% are unknown.  The perception of Utility 21 is that almost all of its failures are cable failures and very few of its failures are accessories. The perception of Utility 4 is reversed.  Utility 4 perceives that about 4 out of 5 of its failures are component failures and 20% or less are cable failures.

If the primary cause of your failures are components, consider which components are failing – terminations or splices or both. There are two injection paradigms, namely Unsustained Pressure Rejuvenation (UPR) and Sustained Pressure Rejuvenation (SPR). See “How to Inject” for more on UPR and SPR. Novinium is the only firm in the world that can use both paradigms. UPR attempts to flow through existing splices, so it is not the best choice if your firm experiences splice reliability issues. SPR replaces 100% of the splices and terminations with modern state-of-the-art components. UPR replaced all of the dead-front terminations, so if those are problematic components for you, UPR will address that issue. Novinium has made several improvements to the safety and reliability of dead-front terminations used for injection. I will describe those improvements another day.

In summary, if your reliability issues are primarily component issues, rejuvenation directly addressed these with systematic component replacement. Depending upon your specific circumstances, the Novinium masters of reliability will help you decide which injection paradigm best addresses your reliability issues at the lowest capital cost.

If your reliability issues are cable-centric, check out my next post in this series, Failure Causes II, where we will ask the question:  What are the primary causes of cable failure and how is each addressed or not addressed by rejuvenation?

Master of Reliability,

Thermo Bull Frog

Real World III – Dominion Dodge

In my last post of 2011, Wondering in Western Washington, questioned the merit of the claims made by UTILX^® in a document titled, “Life Extension Estimate for UtilX^® CableCURE^® Rejuvenation Fluid.”  That document includes 17 pages and numerous claims. In this third of a series of posts, I consider extrapolated life claims scattered across pages 13 through 15.  The author of the document presents a series of arguments built around a cable that was treated with CableCURE^®/XL fluid at Dominion Virginia Power. The 35kV, 3-phase circuit included 1000 kcm aluminum conductors and 260 mils of XLPE insulation. One phase was treated with XL fluid; another phase was left untreated as a control. The cable lies in thermic soil (12-22°C) about one meter deep with no load. In fact, the circuit has had zero load since it was treated. I will share some of the more colorful assertions by the author below, but first the context suggested by the author is that this “real world” example is representative of the population of aging cables. Presumably the reader is encouraged to assume that the measurements made on this circuit can be extrapolated to what I have taken to call, the “real, real world.”  The “real, real world” includes the 7-strand and 19-strand cables that make up the bulk of the rejuvenated cable universe. Like we saw in yesterday’s post, “Real World II – Duke Deception,” the author has not been very vigilant at choosing representative samples.

Point – Counterpoint

“This makes the result very conservative and only useful as an unrealistically low minimum boundary.”

Using very lively language the author appears to coax the reader that the analysis that follows can be applied to any case … we shall see.

“It is generally assumed that the reduction of breakdown strength over time is polymeric slowing over time. Modeling this reduction as a straight line is absolutely the most conservative approach.” 

This frog is reluctant to put words in the author’s mouth, but I believe he meant to say “a polynomial” where he said “polymeric.” Even with that correction the author is still in error. The dielectric degradation slope of solid dielectric cables is best described as an exponential decay or hyperbolic decay … but I am quibbling now. The real point of the adverb-rich language again appears to be to encourage the reader to accept the analysis which follows without undue diligence. This frog will not willingly suspend her disbelief.

“The absolute most conservative evaluation of its remaining life would be to assume that from this moment on (Time = 14 years post injection) its' decay rate is linear and equal to the decay rate of its un-injected counterpart. In other words, we assume for the sake of absolute conservatism that the fluid at this point has no effect on the cable.”

The analysis is not just conservative it is absolutely conservative. It’s difficult for me not to correct the grammar and punctuation, but I successfully restrained myself.

“Assuming that [the treated cable] will age from this point on at the same rate as its un-injected counterpart is obviously nearly ridiculously conservative. By doing so however we are able to arrive at irrefutable proof of injection effectiveness as well as absolute certainty of the absolute minimum value of added life.”

These two sentences are gems. Thinking about the meaning of “obviously nearly ridiculously conservative” is a bit like thinking about one of those science fiction time paradoxes. If I went back in my time machine and swallowed my father when he was a tadpole, how could I have ever been spawned in the first place?  What does “nearly ridiculously” mean? Almost, but not quite, ridiculous? This frog is not sure about that, but I am quite confident the author is trying to sell me an idea I shouldn’t be buying. I can be confident, because if the author actually had irrefutable proof, why would he hide it within the shroud of a “Confidential and Proprietary” document and actually sue his customer to prevent its public disclosure? (See UTILX v. City of Tacoma, No. 11-2-11594-7 in the Superior Court of the State of Washington in and for the County of Pierce.)

Fallacy of the Anecdote II

Putting aside the overenthusiastic use of adverbs and hyperbole the author makes a reasonable case for the efficacy of his product in an unloaded, 1000 kcm, 35 kV feeder cable buried in thermic soil. The problem arises because he holds out this example as one of a handful of “real world” examples and implies that these few anecdotes prove the universal efficacy of his product. The Dominion cable is not representative of the population of “real, real world” cables. In the table nearby I tally up the estimated impact of some differences between this single sample and the “real, real world.” In yesterday’s post, we saw that the Duke cable was off the mark by about a factor of 240X.  The Dominion Dodge is not nearly so egregious. Here the error is a paltry 20X-150X! The author appears headed in the right direction.

Executive Summary

If you have a cable, like the Dominion cable with no load, treatment with even low performance injection fluids should provide several decades of post-injection reliable life. However, that success cannot be extrapolated to 7- and 19-strand cables that carry cyclic loads. The old fluid utilized at Dominion Virginia Power was deployed by a Novinium founder and is available from Novinium for non-demanding applications.  Perficio™ 011 fluid works well in non-demanding applications, like cables with really thick insulation, low loads, and non-constrained conductors. In the decades since the introduction of the first generation of technology, the masters of reliability at Novinium came to recognize that one cannot treat all cables the same. Novinium is the only supplier in the world of patented technology (U.S. Patent 7,611,748) which addresses the full spectrum of cable types and sizes.

Using adverbs sparingly,

Real World II – Duke Deception

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 a bunch of interesting claims. In this second of a series of posts, I consider two claims proffered on the bottom of page 3.  To wit …

“[Micro Infrared spectroscopy is] performed routinely on post injected cables. An example is provided by the published paper [3]; ''Case Study: Rejuvenation Fluid Injection Results from Duke Power's Little Rock Retail Tap Line, a 115kV XLPE, Buried Transmission Circuit."  Figure One shows a chart from that paper demonstrating that the quantity of fluid, even after 10 years, exceeds the target concentration for a six to nine month old injected cable. Two points are established by Figure One. The first is that fluid in optimum injection quantities still exists in the cable's insulation. The second is that the rate of fluid decay is too small to measure after 10 years.”

Notes: Reference 3 above is to a non-peer-reviewed paper provided Stagi & Kimsey at the IEEE T&D Conference (Dallas, TX), May, 2006. An augmented facsimile of "Figure One" referenced above is shown in the graph below in the third illustration. All punctuation and grammatical errors were left as they were found by this frog.

Fallacy of the Anecdote

The author is attempting to make a case for the efficacy of his product.  This Duke cable, and as we shall see in future posts, all of his examples except for the example of Northeast Utilities, is not representative of the population of “real world” cables. Let’s enumerate the problems with this single anecdote.  Of the population of treated cables, the vast majority is single-phase URD cables with 7- or 19-strand conductors. The vast majority has insulation thickness of less than 260 mils and is unjacketed with bare concentric neutrals. The Duke cable has a 61-strand conductor, holding much more fluid and the insulation thickness is three to four times thicker than the population norm.  The Duke cable has a copper taped shield, semi-impervious to permeation, and a 170 mil thick PVC jacket. In the table nearby I tally up the estimated impact of some differences.

All of these differences place the Duke cable among the least representative samples one might choose to make a population extrapolation. On top of the unrepresentative nature of the Duke cable design, the author makes an egregious omission.  The Duke cable was not only treated from the conductor outward, as is the norm within the population of treated cables; the annular space under the cable’s jacket was also treated. The cable was treated from the inside-out and from the outside-in. This highly salient fact is not to be found in the author’s papers or accompanying slides.  Taken together the differences put the Duke cable outside of the norm by about a factor of 240!  That's not 240%; that's 24,000%!

First Assertion:  Fluid remains in optimum injection quantities

In this season of presidential debates, I am reminded of the single Reagan-Carter debate of 1980, which I recently watched on YouTube.  Over and over again, when Jimmy Carter made some bizarre claim, Ronald Reagan would chuckle and say, “There you go again.”  Frog to author:  There you go again – assertion without proof. What precisely are the “optimum injection quantities?”  Are you suggesting that if the concentration profile were say, 20% higher, that the reliability of the cable would be poorer? That notion is silly and directly contradicted by earlier peer reviewed work done on the same cable. I will reference that work in the next paragraph. In the graph that I reproduce nearby, the author presented a green dotted line labeled “Target Concentration,” just below 1.5%_w. If I were a betting frog, I would bet that the Target Concentration was chosen after the micro-infrared data was compiled. How else to explain an utter lack of justification for the figure? There you go again – assertion without proof.

Second Assertion:  Fluid decay is too small to measure after 10 years

There you go again – assertion without proof.  Where is the measurement from 10 years earlier to make the claim?  The author doesn’t provide the data. Fortunately, Novinium houses the world’s largest library on rejuvenation science and a decent comparison can be found there. In the figure nearby I have inset micro-infrared data from the same cable. The data was published in “Cable fault prevention using dielectric enhancement technology” presented in June, 1995, by Novinium’s own Glen Bertini at the peer-reviewed Jicable conference in Versailles, France. The assertion is false.  The average concentration in 1995 was about 3.5%_w, the average concentration a decade later was about 1.7%_w – a factor of two is not too small to measure.

Executive Summary

There is undoutedely a good reason that the author of “Life Extension Estimate for UtilX^® CableCURE^® Rejuvenation Fluid” tried to keep this paper away from reasonable scrutiny. A cynical reader might even think that the author is trying to mislead his audience.  Rejuvenation fluids do in fact improve the performance of transmission cables, but the author would have you believe that treating such cables is a greater technical challenge than treating a 15kV URD cable.  In fact the opposite is true. Cables like the Duke cable should experience extremely long post-injection life, but that success is not easily extrapolated to 7- and 19-strand cables. The old technology used at Duke was conceived and deployed by a Novinium founder.  That technology works well in non-demanding applications like cables with really thick insulation or low loads. In the decades that have transpired since the introduction of that old approach, those who are masters of rejuvenation technology came to recognize that one should not treat transmission cables the same as one would treat a URD cable. Only at Novinium is patented technology (U.S. Patent 7,611,748) available to address the full spectrum of cable types, sizes and flavors. This frog will not employ deception to convince anyone.

Novinium’s Integrity Value: Truth and knowledge are the foundation of the Novinium character. Each will be advanced at every opportunity and neither will be compromised.

Truly yours,

T. B. Frog

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.

Desiccating

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.

Trap

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.

High K

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.

Executive Summary

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.

Real World

Dear Forthcoming Frog-

A bid proposal from your competitor included a report entitled “Life Extension Estimate for UtilX^® CableCURE^® Rejuvenation Fluid,” written by W. R. Stagi of UTILX.  The document is claimed as “Confidential and Proprietary” and makes many claims.  I have reproduced my favorite claim below.

“Assuming that [cable insulation] will age from this point on at the same rate as its un-injected counterpart is obviously nearly ridiculously conservative.  By doing so however we are able to arrive at irrefutable proof of injection effectiveness as well as absolute certainty of the absolute minimum value for added life.”

Tell me if it is true, oh wise one!

Wondering in Western Washington 

Dear Wondering-

I highlighted a few of the phrases from the quotation above, because the language is so colorful.  Where else can you see three adverbs strung together like “obviously nearly ridiculously?”  Where else can you find “absolute certainly?”  And where else can you find “absolute” twice in a single sentence separated by only three words?

I had to see the rest of the document to which you refer.  My team made a public disclosure requests to the City of Tacoma.  I have all 17 pages and I can summarize my reaction by noting the category under which I am publishing this and future posts regarding your inquiry, namely “Crazy Competitor Claims.”  In Future posts, we will examine some of the specifics, but I’ll give you some other hints of the fun we will be having by asking two rhetorical questions.

1.    In any 17 page document where the phrase “real world” was used 26 times, do you think that the pronouncements are really real world?  There are a couple of even more colorful “actual real world” phrases – presumably the actual real world is even more real world than the regular real world.

2.    Why would the author of the document try so hard to keep secret, irrefutable proof?

I will answer these and many more questions in 2012.

Sunlight has a way of revealing the truth,

Thermonuclear B.F.

O-ring Evolution

Dear Erudite Amphibian,

If an O-ring equipped probe of an injection elbow were to break-off or otherwise fail, can we replace it with a standard probe?

Wondering in Washington

Dear Wondering-

The absolute best choice is to replace the damaged probe with an identical probe. Novinium would be happy to provide these probes to you with only a modest markup. If the Novinium masters of reliability are in town, just give them a call as they likely will have spares on their truck. This frog realizes that your question is probably targeting the case when there are none of these O-ring equipped probes nearby and you desire to put the cable back in service. To answer that question it is useful to explain how the O-ring-equipped probe evolved.

In the illustration nearby, I point at a fully evolved O-ring on a probe pin.  In this 2011 incarnation the O-ring is seated in a composite sleeve molded into the elbow throat. The very first injection elbows were invented by my colleague, Glen Bertini and his associate at Dow Corning, Dan Meyer, about 25 years ago.  I wish I had a picture to show you, but I don’t believe any exist of that dinosaur.  The very first injection elbow, used from 1987 to 1989, was a standard elbow with a capacitive test point.  Bertini and Meyer drilled and taped a hole through the capacitive test point and screwed an insulating nylon cap into the hole.  The elbow worked flawlessly, but was properly considered unreliable for long term operation and hence the elbow was treated as a tool.  After the injection was complete the modified elbow was swapped for an unmodified elbow of the same size. There was no O-ring in either elbow.  CableCURE^® 2-2614 fluid, which was (and remains) predominately phenylmethyldimethoxysilane (PMDMS) and has a flash point of about 66°C flooded the bushing on 100% of the applications.  There were no adverse consequences observed.

The next improvement in the injection elbow was the introduction of a dedicated interference fit injection port.  The collaboration between Bertini and Meyer of Dow Corning and Alan Borgstrom of Elastimold yielded two U.S. patents, 4,946,393 and 5,082,449 in 1989 and 1990.  This advancement meant that the injection elbow could be left in place indefinitely … only the injection cap had to be swapped. There still was no O-ring, hundreds of thousands of feet of cable were injected, and there was precisely one problem. Sometime in late 1989 a bushing failed because the CableCURE 2-2614 fluid had dissolved a plastic component within the bushing. Elastimold and Dow Corning immediately tested the fluid and bushing component compatibility and found no issues that detracted from the elbow-bushing compliance to IEEE 386™.  See Elastimold test reports 102-17-9011 and 101-17-9010, both dated January 1990.

168 1990 (102-17-9011) - IEEE 386 15kV with fluid.pdf (135.13 kb)

274 1990 (101-17-9010) - IEEE 386 25kV with fluid.pdf (134.51 kb)

It turns out the single bushing that failed was an anomaly – not a large production bushing. None-the-less, Dow Corning and Elastimold decided that even though incompatible bushings would be a rarity, it would be prudent to add a seal to the system to minimize the probability of adverse fluid interactions within the bushing.  An O-ring was added to the probe in about 1991.  The rubber O-ring was not seated in a rigid collar and hence a small deflection of the probe pin would allow a leak. This problem was minor, however, because when the elbow was seated on the bushing it was held in a perfectly centered position.

Two years later in about 1993, UTILX^® Corporation, after licensing CableCURE technology from Dow Corning, unveiled another Bertini inovation (U.S. Patent 5,372,841), which was called CableCURE^® XL fluid. While XL fluid brought significant dielectric performance gains, it suffered from a much lower flash point and it wasn’t too long before the imperfection of the O-ring seal lead to fires when a fluid-filled elbow was switched.  Over the course of the next decade, the seal was changed several times to improve its robustness.

Novinium fluids are not flammable. See my November 2, 2011 post “Fluid Flammability” for more on this subject. If you are using a flammable fluid from another supplier, this frog would highly recommend using only O-ring probes.  With Novinium fluids the risk is minimal.  There is a low risk that fluid will get into the bushing after the injection has been completed, and that risk decreases as time-since-injection advances.  There is an even lower risk that Novinium fluids in the bushing will create any safety or reliability issues.

In 2012 Novinium and our component manufacturing partner will be introducing an entirely new injection device suitable for both unsustained pressure rejuvenation (UPR) and sustained pressure rejuvenation (SPR).  It will be inherently leak-free. When the new injection device becomes commercially available, switch to it and your question will become moot.

Evolving to be safer, faster and better,

Thermo

EPR (Part 2 of 3)

In yesterday’s post, EPR (Part 1 of 3), I provided a response to the inquiry of Ethel P. Reliability on whether it made sense to rejuvenate aging EPR cables.  The short answer was yes and I dispelled some EPR myths along the way.  This post explores the chemistry of EPR and dispels another myth suggested by a physicist at the ICC meeting.  I won’t use his name to spare embarrassment, but he is often critical of others who speak without actual knowledge or evidence … a sin this frog does not commit.  The gentlemen suggested that the silanes in rejuvenation fluid might interact in some nefarious way with the silane surface treatments employed in the manufacture of EPR compounds. 

First some background

EPR or ethylene propylene rubber comes in several flavors – often designated with colors. All EPRs are roughly half rubber – the balance is filler.  Modern EPR materials use treated clays as the filler and their color varies from gray to brown to pink.  Some early EPR compounds were filled with carbon black and these are referred to as Black EPR.  Today we are going to limit our discussion to clay-filled EPR.  Those who manufacture EPR hold the details of their clay formulations close to their vests.  There are several clays including hectorite, beidellite, montmorillonite, and kaolinite.  All share several chemical properties.  All include silicon as their most prevalent low electronegative atomic constituent and all include hydroxyl groups (oxygen bonded to hydrogen represented as “-OH”).  The hydroxyl groups are connected most commonly to silicon, and less commonly to aluminum, magnesium, or lithium.  These hydroxyl groups, illustrated nearby are polar in nature and incompatible with the organic ethylene-propylene polymer. To improve the compatibility of the clay with the rubber, compounders treat the surface of the clay with silanes very similar to rejuvenation compounds. These silanes form oxane bonds, largely eliminating the hydroxyl groups. For all practical purposes these reaction are permanent – that is the silanes are permanently bonded to the clay surface. One purpose of this surface treatment is to ensure uniform dispersion of the clay in the polymer during processing. Another advantage of silane treatment of the clay filler is a reduction in the effective solubility of water in the EPR compound, because of the replacement of the hydrophilic hydroxyl groups with hydrophobic silicone. 

There is no evidence that anything in any treatment fluid interferes in any way with EPR. In fact, the opposite is true.