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. 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 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

 Voltage Constraints

Dear Abundant Amphibian,

At our monthly staff meeting yesterday afternoon, I made the presentation on our cable rejuvenation project and I believe it was well received.  I appreciate the information and PowerPoint slides that your most excellent sales representative supplied.

I did have one question asked that I did not know the answer to – what is the voltage limit of the process?  I am sending an e-mail to our department director concerning our project and the benefits of the rejuvenation process in general and I would like to include the answer to that question if possible.

John

Dear John-

The highest voltage ever rejuvenated was 115 kV.  As a practical matter there are not many solid dielectric cables at voltages above 115 kV that are not water-tight designs.  However, if there were we would love to treat those too.  You see the thicker the insulation the easier it is to treat the cable.  The rate of fluid exudation, that is the rate the fluid leaves the cable, is slower the thicker the insulation.  Our most technically difficult challenge is the 110 mil thickness 5 kV cables.  So there really is no upper limit.

In 2012 we will be unveiling new products to deal with lower voltage cables, so we will be able to treat any solid dielectric cable – any voltage, any non-filled stranded conductor.

Any voltage – any time,

Thermo

 Bursting a Bubble

Frankest of Frogs,

I need a written response to my inquiry.  I will use your response as a basis to NOT inject #2 copper cable that was installed prior to 1970.  My stance is that there has been an instance where this older cable has burst during injection due to loading and geometry changes and should be replaced. Your comments would help substantiate this claim.

Sincerely,

Albert A.

 Dear Albert-

I’m not sure you will be able to use my comments to substantiate your claim. While you are exactly right that “… there has been an instance where this older cable burst during injection,” it is also true that about 9,999 cable segments of similar vintage have not burst during injection.  Put another way, bursting cable has historically occurred in just 0.01% of injection cases – success is realized 99.99% of the time! There aren’t many things with that level of performance.  And even for that single case, the burst occurred, because the cable was eccentric and did not meet the minimum insulation thickness requirements of Table 4-7 of ICEA S-97-682-2004 of 4.19 mm. This lonely case was described in some detail on Page 5 of ...

“Silicone Injection: Better with Pressure”

... presented in Subcommittee A of the Insulated Conductors Committee (ICC) on May 19, 2009. I have reproduced Figure 9 from that paper above.

Reliably yours (at least with four nines),

T. B. Frog

Flowing Through Splices

Dear Wisest of Frogs,

We have been proactively injecting cables with the unsustained pressure rejuvenation for years.  Many of the cables we seek to treat have existing splices and we have always attempted to flow through the encountered splices. I understand that Novinium will use the same approach if required by the circuit owner, but you seem to frown upon the practice. Why the frowning face? Why will you inject through splices if you don’t think it a productive practice?

Seeking the easy way,

Qui Transtulit Sustinet

Dear Sustinet-

Any state that has a Latin motto is a state near and dear to me! The most common translation of the Connecticut state motto is, “He who is transplanted still sustains.” And what the heck is that supposed to mean?  The origin of that motto is uncertain, but with my skills in Latin, I have an alternate translation that better captures what its framers had in mind – to wit, “A splice replaced is more reliable.”

There are three inherent uncertainties about flowing through unexcavated direct buried splices.  The first uncertainty: One seldom knows what kind of splice is there. Design and compound chemistry are the most common uncertainties. Splices might fall into one of three categories – okay, bad, and ugly.

The second uncertainty is the quality of the craftsmanship that went into the splice.  Some circuit owners have had very few component failures.  Is your firm one of the lucky few?  Novinium’s master craftsmen are all trained and certified to exceed the emergent IEEE P1816™, “Guide for Preparation Techniques of Extruded Dielectric, Shielded Cable … and the Installation of Mating Accessories.”  Novinium had a hand in the creation of the P1816 Guide and is the only firm in the world that offers training and certification to the Guide. Novinium shares this knowledge on its eLearning website at www.knovinium.com.

Finally, while air pressure tests are typically employed to confirm that a splice or splices in a cable will support a minimum anticipated pressure, it is not possible to know with certainty whether rejuvenation fluid, with its inherently low surface tension, will leak across the splice-cable interface. The leaking of a dielectric fluid across an interface has one certain issue and two potential issues.

• Certain issue: The quantity of fluid intended to treat the cable insulation polymer will be less than planned. If the leakage is significant, such a leak will reduce the anticipated post-injection life of the cable.
• First potential issue: Leaking fluid may carry particles, such as suspended carbon black or aluminum oxide, along the splice-cable interface. Such particles may contribute to interfacial tracking.
• Second potential issue:  Rubber splices absorb a substantial amount of treatment fluid intended to treat the cable.  This phenomenon was described in the November 1, 2005 paper “Improving Post-Treatment Reliability: Eliminating Fluid-component Compatibility Issues” presented at the ICC C26 Discussion Group. Click here to get a complete picture of this issue.

The Novinium masters of reliability seek the unattainable – perfection – 100% post injection reliability.  We are at 99.4% today and climbing. See Crow for the data. If you are attracted to the idea of kicking today’s problems down the road for your successors to deal with, you might want to consider a career in U.S. national politics. The electorate has a proclivity to elect folks that are unwilling to deal with problems, even when they are easy to recognize. Unlike the beltway crowd in D.C., this frog doesn’t believe in kicking today’s issues down the road only to address them again later – fix it, fix it right, and fix it right now!

To circuit owners, I dispassionately explain the economics of the two approaches and do a little cheer for the most economical approach.  The circuit owner decides and I say, “Yes, ma’am!” At the end of the day, some circuit owners are devoted to a less enlightened path. I believe this is generally so because of inertia.  That is, flowing through splices has been practiced for two decades, and it works decently enough. The economics are more favorable than replacement alone. Once circuit owners experience the more enlightened Sustained Pressure Rejuvenation (SPR) approach and get a chance to enjoy its benefits, it is generally embraced.

In a future post I will explain Integrated Rehabilitation, which is the ultimate approach to rehabilitating underground cables.

Reliably Enlightened,

T. B. Frog

 Crow

Dear Frog of Knowledge,

Can you explain the Crow-AMSAA graph on Novinium’s web site at novinium.com/lessons.aspx?  How do I compare Novinium’s post-injection reliability to that of UTILX?

Not wanting to eat crow,

‘raven Reliability

 Dear ‘raven-

What a great play on words! My fans that compose creative questions get to move right to the front of the queue.  You are justified in “c’raving” reliability. I took the opportunity your inquiry provided to update the Novinium failure statistics through August 10, 2011. I present those statistics in the chart nearby. Crow was a guy that worked for the “Army Material Systems Analysis Activity” or AMSAA.  Crow developed the statistical model that now bears his name and that of his employer.  Crow-AMSAA or “C-A” for short is widely recognized as a preferred model to predict the reliability of complex systems that experience multiple failure mechanisms.

The x-axis is the product of the feet of cable that have been treated by Novinium and the years that have elapsed since treatment.  For example, if a 328 foot (100 meter) length of cable was treated three year ago, its contribution to the cumulative treated would be 984 feet*years.  The x-axis is logarithmic.  Plotted against the y-axis are the failures – 56 in total.  A least squares regression of the failures provides a slope, or beta, of 0.64.  A beta less than 1 means the failure rate is decreasing.  Process and chemistry improvements, together with the improving mastery of the Novinium’s craft workers, make Novinium technology more and more reliable.  That’s not to say that when Novinium began injection operations over six years ago post-injection performance was unacceptable.  Novinium started where the old technology, invented by Novinium founders, reached a reliability plateau. When I did this same C-A analysis nine months ago (November 2010) the beta was 0.72.  So, not only is the failure rate decreasing, but the rate of decrease is accelerating!  About 99.4% of all the cables, which Novinium have treated, remain in reliable service.  This is at least twice as good as the other guys!

With regard to how you can compare Novinium reliability with that of UtilX, I can only provide you with some frog-advice. As a circuit owner you should demand that UtilX publish its total failure statistics – not just a few select circuit owners, the whole data set.  Then circuit owners would be able to make an apples-to-apples comparison. Don’t hold your breath, when NEETRAC, their sponsoring circuit owners, and other industry leaders invited UtilX to participate in a side-by-side laboratory experiment, UtilX helped craft an experiment, but withdrew their participation when the experiment actually began.  By the way, that experiment is complete and included the only rejuvenation firm willing to share their post-injection results in a truly independent experiment – that would be Novinium. UtilX demurred, citing “business and commercial reasons.”

No need to crow when you can croak,

T. B. Frog