Neutral Corrosion & Novinium Warranty

Dear Informed Frog-

I have been asked to pursue something in writing concerning the 50% neutral corrosion and Novinium’s warranty. I respectfully request to have this from Novinium by quitting time this Friday, January 25, 2013. Thank you in advance for your cooperation in this matter and feel free to call me with questions or problems.

Signed,

Corrosion Concern in Colorado

Dear Concerned-

Short Answer

Go to …

http://www.novinium.com/Warranty.aspx

… and search for the word “corrosion” … you won’t find it! The warranty is purposely silent on neutral corrosion.

Less Short Answer

To understand why the short answer is so short, it is really useful to understand the purpose of the neutral and the consequences of various levels of neutral corrosion on the performance and reliability of the cable. To this end, view the recording of the September 2012 Webinar or read the webinar’s companion paper, “Neutral Corrosion – Significance, Causes & Mitigation”  prepared and presented by some of the cable experts at the Insulated Conductors Committee of the IEEE that created IEEE 1617™, the IEEE "Guide for the Detection, Mitigation, and Control of Concentric Neutral Corrosion in Medium Voltage Underground Cables."

Based upon IEEE 1617 and the aforementioned webinar many circuit owners have chosen 50% corrosion as their cutoff point for rejuvenation. But you get to make that determination yourself. You need only to communicate your wishes to the Novinium masters that proide your services. If you would like to discuss your choice with an expert … you can find them at Novinium. As you will learn in the webinar the 50% rule-of-thumb is a “glass half-full” proposition, because the rate of corrosion in direct buried cables declines over time. The pessimistic “glass half empty” perspective is not supported by observation.

Even if you have the occasional neutral corrosion in excess of 50%, don’t despair. The corrosion can be pinpointed and repaired, generally at a fraction of the cost of replacement. The webinar explains that option too.

Neutral on neutrals,

Thermo

A Cable Too Long

Dear Felicitous Frog,

I am currently reviewing a URD circuit with a cable segment that is 6,200' per our one-line and GIS.  It is our regular #2 db [direct buried] cable.  I am considering the installation of pull-boxes to break up the many long segments prior to attempting injection. What is the practical limit to TDR [time-domain reflectometer] testing?

What is the practical injection limit?   I assume in the best case that there at least a construction splice every 2000 feet, but there may be more that have to be replaced. 

Curious about cable  

Dear Curious- 

For background on how TDRs work, check out my October 1, 2011 post, “Reflections on a TDR”. A TDR sends a radar-like pulse down a cable. Like radar, a portion of the pulse is reflected when it “hits” objects along the cable path. Objects are anything that has a modestly different impedance (resistance, capacitance, and/or inductance) from that of the cable. Splices, cable ends, and neutral corrosion are generally identifiable. These objects are often called impedance anomalies, because the impedance varies locally from that of the cable.

There are two phenomena that reduce the acuity of the TDR – attenuation and dispersion. In the image nearby I illustrate the practical effects of attenuation and dispersion. As a wave travels along a cable its amplitude decays because no cable is without loss. When a male bullfrog croaks into a pipe, the volume decreases with distance because the sound wave amplitude attenuates. The attenuation is due to the imperfections in the molecular collisions. A portion of the sound waves are converted to heat. The same thing happens in the cable as electrons bounce among the cloud of conductor d-orbitals.

The second effect is dispersion and it too is the result of imperfections. Instead of loosing energy, dispersion smears energy because the rate that the signal moves through the cable is not uniform through its cross section. Skin effects and twisted stranding act to disperse the wave. Copper tape neutrals have a particularly nasty dispersion.

Simply recognizing these two effects helps the skilled operator interpret the observed wave shapes. Longer cables and those with more splices or corrosion will have shorter and more dispersed reflections.

Tactics to Improve Acuity

Of course the operator can use the TDR from both ends of the cable. This tactic effectively doubles the TDR’s resolution.

The next choice in the operator’s toolbox is to increase the pulse width. At the expense of resolving smaller or closely spaced impedance anomalies, wider pulse widths are the brute-force way to overcome both attenuation and dispersion.

A third choice is to divide and conquer.  Each construction or repair splice that is excavated provides an opportunity to TDR the two subsegments of cable from the splice in each direction.

Every cable is different, but more than likely the TDR should be able to identify all of the splices on a 6,200-foot run of No.2 URD cable employing just one or two of the aforementioned tactics.

Injection Length Limits

At Novinium, we know no bounds. We have a variety of patented injection paradigms to address long cable lengths. The preferred method for such a cable is sustained pressure rejuvenation (SPR). With SPR subsegments of cable are injected from termination-to-splice and from splice-to-splice. As you suggest, the longest run would likely be 2000 feet, the typical length of a cable reel. We have a model that allows us to predict injection times with great precision. Assuming your No.2 cable has round strands and 175 mils of XLPE insulation, a 2000-foot run utilizing SPR would require about 46 hours of injection time. We have treated cable subsegments that are several miles long and we have additional tools available for the most challenging circumstances.

With SPR the cable subsegments are typically deenergized during the injection process. If having the circuit deenergized for several days is not palatable, Novinium has still more tools at its disposable including flow-though splice technology that supports SPR. Of course, your suggestion of creating shorter subsegments by installing intermediate pull-boxes is another choice that can reduce the injection time.

Flow through really long runs of cable using older approaches is problematic. The challenges and the solution for really long cables, like submarine cables, are included in U.S. Patent 7,976,747 and in the paper, “Advances in Chemical Rejuvenation of Submarine Cables” presented at the Jicable conference in Versailles France in June 2007. To review this paper click here.

In short, we have many tools to address every conceivable situation. Talk to our crack field engineering team to explore all the options, or write back to me with more details and constraints. Check out our senior field Engineer Norm Keitges splashing in Puget Sound. He must have thought for a moment that he was a frog, because we generally frown on humans swimming on the job.

Bending boundaries,

T. B. Frog

Wet, Wetter and Wettest

Dear Soggy Froggy,

I have two areas under consideration for rejuvenation next year.

• The first is a sub-division with 40 year-old cable that is in relatively dry sandy soil.
• The second sub-division has 15-20 year-old cable that is in very wet, swampy soil.

All other things being equal, which area would enjoy the greatest benefit from rejuvenation? Is there any data to support the recommendation? I hypothesize that the cables in the swampy soils should be injected first, since those cables are constantly in water and injecting them might yield the greatest benefit.

Wet, Wetter and Wettest

Dear Wettest-

It’s true that I have a personal preference for the swamp, but I won’t let that predilection alter my advice. This is a really great question because the wetness of the soil at one meter depth is not often discussed and often misunderstood. Fortunately one of my colleagues wrote a paper cited below that unearths the truth of the matter.

Bertini, “Molecular Thermodynamics of Water in Direct-Buried Power Cables,” IEEE Electrical Insulation Magazine, Nov/Dec 2006.

I would encourage my readers to review that paper in its entirety as it dispels many common myths. However, I asked the author to summarize the portion of the paper that relates specifically to your query and he has done so in a YouTube video. Watch this video and learn why both populations of cable are equally wet.

In your inquiry you say, “All other things being equal.” But are they really equal? I would suggest that the first criteria should be: Which of the two areas has had the greatest reliability issues per foot of installed cable? If reliability is equal, I would use age as the next best predictor of future performance.

Forever wet,

Thermo B. Frog

Fabric Tape Conductor Shield

Dear Amiable Amphibian,

I am wondering if you can provide some thoughts or comments on a cloth fabric semi-con we have here on some older #2 Cu cables, 15kV. Does the Ultrinium fluid harm this fabric?  Does the fluid react with any semi-conducting materials like carbon? Does Novinium think the injection process disturbs or harms the fabric?

Conducting Query

Dear Conducting-

The fabric tapes used on pre-1980 vintage cables were carbon-black dispersed on cotton fibers. Neither the cotton nor the carbon black in these semiconducting tapes react with the silanes used with Ultrinium™ fluid or Perficio™ fluid. In fact, cables with fabric tapes have been treated with alkoxysilane rejuvenation fluid for over two decades. Novinium has not experienced a single failure of a cable with a taped conductor shield.

The use of taped conductor shields in medium voltage distribution applications all but halted by the mid-1970’s in North America. Bartnikas and Srivastava relate in Power and Communication Cables, page 83 …

“Semiconducting carbon black tapes were … used as shields in the early linear polyethylene (PE) insulated cables. Due to poor adhesion between the tapes and the PE as well as occasional breaks or gaps between butting edges of carbon black tapes themselves, partial discharges often occurred within the voids formed at these faults. Polyethylene cables using carbon black shielding tapes were also found to be highly susceptible to tree growth.”

The fact that you have some of these cables in service today is testament to the absence of partial discharge and hence these particular cables do not suffer from the poor adhesion, occasional breaks or gaps which Bartnikas and Srivastava warned about in their book. However, there are certainly water trees and I’ll bet they’re doozies.  Fortunately, ameliorating the pernicious effects of water trees is precisely what Ultrinium and Perficio fluids are designed to do.

There are two operational considerations when injecting taped conductor shield cables. First, there is much more room in the strand interstices, so the fluid will flow faster and the cable will hold more fluid – these are both good things.  Second, when fluid flows through the strands it will entrain some un-adhered carbon black, so the outlet fluid will be black. Not to worry, there is much more where that came from and there is no need to try to flush it all out either.

Yours truly,

Thermo B. Frog

Better Than New

Dear Learned Leaper,

Why would I use rejuvenation, when I can have new cable?

Cable Guy

Dear Cable Guy-

I suspect, Cable Guy, that you’re not a circuit owner. Do you work for one of the cable manufacturers? If you were a circuit owner, you would know that money does not grow on trees and rejuvenation is almost always considerably less capital intensive than wholesale replacement. The question would have had more merit had it been asked two decades ago when the first generation of rejuvenation technology was becoming commercially important. The anticipated life of the first generation of fluid in non-demanding applications was and remains about two decades. The generally anticipated life of post 1990-vintage cables is about four decades. The 2X difference in anticipated life complicated the economic analysis of the treat or replace question. Advanced technology from Novinium can provide the same four-decades of service life, so that issue is a relic of the 20^th Century.

How about post-injection reliability? In the January 31, 2012 issue of the Las Vegas Regional Journal, it was reported that NV Energy experiences about a 0.6% failure rate when it replaces cable. NV Energy reports that the older injection approach has about the same failure rate over a 12-year period. Utilizing Novinium’s state-of-the-art technology and the outstanding craftsmanship of our service delivery experts, our overall failure rate is less than 0.4%. That’s about 33% better than the failure rate of new cable. Novinium rejuvenation technology is better than new! But, here’s the really cool part, Novinium technology and delivery methodology continues to improve! In the graph nearby I am pointing at the beta value of our Crow-AMSAA analysis of all of the faults we have ever experienced treating millions of feet of cable on three continents. The value is 0.56. A value less than one indicates that the failure rate is decreasing – a one would mean that it is staying the same, and a value greater than one would indicate deteriorating reliability. To learn more about Crow-AMSAA, check out my August 11, 2011 post, “Crow.”

Novinium announced the passing of the “Better than new” milestone today. Click here to read the press release. We periodically post a transparent summary of our failure history at novinium.com/Lessons.aspx.

Better next year,

Thermo B. Frog

Suitable for Treatment

Dear B.F.

We’ve taken some photographs of cable samples identified with off-line PD testing.  I was hoping to get your opinion of the cable and if injection would be able to address these issues.

·        On two samples, we found the XLP insulation was a greenish color.  We’ve never found cables discolored before and it had an odd odor.  Upon wafering and dying the sample, quite a few trees were found.

·        On three samples, we found spots where a hole was burned through the semi-con layer and dirt had gotten between the semi-con and insulation, causing some deep pitting.

I’ve attached some photos of the issues.  Neither of these cables has been treated, but can they? Let me know what you think.

Wishing you well,

Wisconsin

——————————————————————————————————————————————————————

Dear Wisconsin-

First off – green is a lovely color and you should be proud of your sample’s hue. The green color proves that the insulation compound manufacturer included anti-oxidants in its formulation and is generally an indication of recent heat exposure. The sulfur-based anti-oxidants break into by-products as they do their job. Some of these by-products absorb red light, leaving a predominantly yellow to green hue. The insulation may by 4201 made by Union Carbide, now Dow Wire & Cable. Click here to check out a fact sheet put out by the Dow folks called:

Color Indicates Presence of Antioxidants in XLPE Insulation Compounds

With regard to the odor, I can’t answer definitively for two reasons. One, you did not send me a sample and two, frogs are not known for their olfactory prowess. I can, however, speculate. The sulfur-containing anti-oxidant by-products are called thiols or mercaptans and have strong garlic-like odor. I have a cat at my house with an exceptionally keen nose. If you send me a stinky sample I can ask her to identify the chemistry involved. I hope it does not smell like tuna fish — she might gnaw on it. See "rats" below.

With regard to the water trees, you will find those in every solid dielectric cable. Water trees are the predominant cause of solid dielectric cable failure. Fortunately, Novinium provides fluids that can reverse the damage caused by water trees and replace the anti-oxidants that have been consumed over decades of field aging.

·        Click here to learn how you can know that water trees are the predominant cause of cable failures.

·        Click here to learn how you can be confident that rejuvenation will reverse the damage caused by water trees.

·        Click here to learn how Novinium^®-brand Ultrinium™ fluid can replenish the anti-oxidants in aged cable.

Deep Pitting

I don’t know if the cable with the holes in it smelled like garlic, but the rodents that chewed on it must have liked the odor.  I doubt that the meal was satisfying. I am fond of rodents. An adult mouse fills my belly for the better part of a week, but I might have taken a pass on the gal that was chewing on your cable. Shreds of polyethylene in her belly would end up in mine and would undoubtedly upset my delicate digestion. I suspect the rat stopped chewing when she started to feel a tingling in her mouth – those were partial discharges. Persistence would have led to an untimely end. That’s how I know the rat was a female. A male rat would not have been smart enough to back off when he felt the tingles … in fact they probably would have only encouraged him more.

Here is a question for you, Wisconsin. How many cables had to be examined to find these rodent bites? If rodent damage is rampant in your service territory, off-line partial discharge testing might be a useful tool to find where the rats reside. It is true, that rejuvenation cannot address rodent damage, but how prevalent is this failure mode? For some insight on that question check out my three-part postings of January 2012 …

Failure Causes I, Failure Causes II, and Failure Causes III.

The Novinium masters of reliability have been involved in the injection of many millions of cable feet. Cables with water trees, with or without interesting color and odor, are handled easily and these represent the frog’s share of the root causes of cable failure. Add in component issues addressed by rejuvenation and a tiny minority of potential issues are left unaddressed. It is for this reason that more than 99.4% of all cable treated by Novinium enjoy failure-free reliability.

Never put anything in your mouth that can kill you,

T. 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.

EPR (Part 1 of 3)

Dear Grandest of Frogs,

I was in the audience of an ICC (Insulated Conductor’s Committee) discussion group C30 (Extending the Life of Field Cables) and was confused by the discussion about treating EPR cables. There were some in the room who seemed to be of the opinion that rejuvenating EPR cables is not appropriate.  Does it ever make sense to rejuvenate EPR cables?

Regards,

Ethel P. Reliability

Dear E.P.R.-

I was not at the meeting in question, but I have several very good friends who were, so I got the straight scoop.  First there was a bizarre suggestion that those who originally invented rejuvenation technology never intended to treat EPR cable.  Two gentlemen who were actually there for the original inventive step of modern alkoxy-silane-based rejuvenation technology were founders of Novinium and are able to confirm that claim is without merit.  The target of the development effort was solid-dielectric cables – EPR cables fall within that genre.  There were several very vocal proponents of EPR cable at that meeting and they were united in a common narrative.  To wit, EPR cables do not fail, they do not suffer water treeing, and hence rejuvenation is counterproductive.

Poppycock!  Poppycock!  Poppycock! Let’s take those assertions one at a time.

EPR cables do not fail

EPR cables do fail.  One laboratory (Cable Technology Laboratory or CTL) that studies cable failures on a routine basis reports that over three decades they have received about 600 samples of failed XLPE cable and about 10 samples of failed EPR cables.  At first glance, one might say that this anecdote suggest a 60-fold reliability advantage for EPR cables over XLPE – that assumption would be exagerated, because about four-times more XLPE cable was deployed from 1964 to 1980 (See Forrest, “Predicting Medium Voltage Underground Power Cable Failures and Replacement Costs,” Western Electric Power Institute, Apr. 8, 1997).  What would be fair to say is that over the course of the last three decades, the reliability of 1960-1980 vintage EPR was about 10 to 15 times better than the same vintages of XLPE cables.  Historically more reliable, yes … invulnerable, no … in need of rehabilitation at some point, yes.

EPR cables do not suffer water treeing

It is true that imaging water trees in EPR cables is quite challenging. EPR cables are filled with clay and as a consequence even very thin samples are opaque.  Traditional microscopic examination with staining often fails to reveal water trees.  A colleague at CTL has figured out a way to image trees in EPR.  Bogdan Frysczyn’s annotated images nearby show bow-tie and vented water trees right at the failure breakdown channels in so-called “pink” EPR.  Similar images have been made for brown and black EPR too.  So much for that narrative.

Rejuvenation of EPR would be counterproductive

Now that we have established that EPR cables do fail and that they suffer the same water treeing phenomenon as XLPE cables, it would seem to be self-evident that rejuvenation would benefit aging EPR cables.  Over a  decade ago, my friends over at CTL together with EPRI (Electric Power Research Institute) and Reliant Energy (Houston) wrote a paper demonstrating just this entitled, “Extending the Service Life of Ethylene Propylene Rubber Insulated Cables.”  In this paper, the authors concluded:

• It is feasible to upgrade early vintage black EPR cable and achieve a significant increase in ac and impulse voltage breakdowns.
• It is feasible to upgrade current vintage pink EPR cable and achieve a significant increase in ac and impulse voltage breakdowns.

These results were based on treatment with phenylmethyldimethoxysilane (PMDMS), which is the primary ingredient in both CableCURE^®/XL fluid offered by UTILX^® Corporation and Perficio™ 011 fluid provided by the Masters of Reliability™ at Novinium. In two subsequent posts, this frog will explain another misconception perpetrated at the last ICC meeting (EPR 2 of 3) and how the technology has advanced over the last decade to improve the post-injection reliability of EPR cables specifically (EPR 3 of 3).

Eternally Proactively Reliable,

Thermonuclear B. Frog