by Thermo 21. May 2013 21:31

Shields Scotty

Inquiry

What impacts do rejuvenation fluids have on the conductor and insulation shields?

Response

With Star Trek Into Darkness in the theaters it was appropriate to revisit the question of shields. Not the shields that deflect Klingon disrupter blasts, but the conductor and insulation shields used to smooth electrical stress in underground power cable. When rejuvenation technology was first introduced about 25 years ago, that was one of the first questions that had to be resolved.

The table below provides some publically available data from a report prepared by Cable Technology Laboratories titled “Testing of VEPCO 35kV cable 5 Years After Upgrading,” dated May 28, 1999. The data examined the impact of a 70:30 mixture of phenylmethyldimethoxysilane and trimethylmethoxysilane (the white phase) and dimethyldimethoxysilane (the blue phase) in an application at Virginia Electric Power, compared to the untreated control (the green phase).

In short, both rejuvenation fluids show slight, but insignificant increases in volume resistivities of the conductor and insulation shields, four year after treatment at both 22°C and 90°C. In all cases, the increase is well below the limit set for cables of that vintage. The more modern limit is even more forgiving than the 1971 values. Dozens of such measurements were made in the last century, but they ceased to be interesting, because the impact was repeatedly insignificant.

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Rejuvenation Science

by Thermo 26. January 2012 12:43

Failure Causes III

In my January 24th 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. We learned that 39% or more of all circuit failures are component failures and that these reliability issues are directly addressed with a rejuvenation program.  In yesterday’s post, “Failure Causes II,” we learned that more than 78% of the cable failures, which represent over 60% of the circuit failures are directly caused by water trees.  78% times 60% yields 47%. Water trees are the root cause of more than 47% of circuit reliability issues. Taken together (39% plus 47%) component issues and water trees account for more than 86% of all circuit reliability issues. We could stop right there, because 86% could be characterized as the vast majority. We could stop right there, because of the over 100,000,000 feet of cable rejuvenated over the last two-and-a-half decades, over 99% continue to provide reliable service. Cables treated by Novinium enjoy a post-injection failure rate less than half that of the industry-wide figure. We could stop there, but we won’t. The Novinium masters of reliability strive for post-rehabilitation reliability perfection.

If component issues and water trees represent the frog’s share of reliability root causes, what are the secondary issues? And how does rejuvenation technology address, or not address, these issues?

Neutral Corrosion

The occurrence of neutral corrosion within the population of bare neutral cables is 100%.  But don’t despair, the occurrence of neutral corrosion that creates safety or reliability issues is an order of magnitude less significant than circuit failures from all other causes – that is, generally 1-2% of cables suffer substantive neutral issues. Click here to check out my July 7, 2010 post along with its links to other published works. Even though the neutral corrosion issue is less significant than many assume, the good news is that neutral corrosion is both detectable and addressable. In fact, the Novinium masters routinely detect and repair neutral corrosion.

Thermal Issues

When cables are heavily loaded over sustained periods the insulation loses anti-oxidants and plasticizers. Oxidative degradation and polymer embrittlement contribute to a decrease in dielectric strength and in severe, but rare, cases may lead to cracking of the insulation. Designed to stay in the insulation for decades after injection, Novinium’s Ultrinium™ 73X fluids include anti-oxidants (AOs) and plasticizers. These materials all but halt oxidative degradation and embrittlement. Anti-oxidants have also been proven to slow the rate of water tree growth and increase the inception voltage of electrical trees. Click here to learn more about anti-oxidants in my March 14, 2011 post, “AO, AO … It’s home from work we go.” If the insulation gets hot enough the conductor may migrate and the insulation will become eccentric. These eccentricities usually manifest themselves at tight bending radii. The Novinium masters identify and remove most excessively bent cable sections. These most commonly occur near terminations or accessible splices and these areas are inspected during pre-injection preparation. Novinium® brand rejuvenation addresses all of these thermal issues.

Halo

Halos are unavoidable when a cable is thermally cycled in the presence of water. 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 is referred to as a halo. In the absence of water trees or some other defects, a halo does not lead to failure, because the halo size is limited by the molecular thermodynamics of water in the polymer. None-the-less, rejuvenation reverses most of the dielectric degradation caused by halos by filling the micro-voids with more compatible organo-silicones. Novinium® brand rejuvenation addresses halos.

Manufacturing Defects

Voids, protrusions, contaminants, eccentricities, and skipped shields are “unwanted features” of a new cable. With the possible exception of skipped shields all of these unwanted features are in every cable. Fortunately for your newer purchases the magnitude of the defects is low enough that the cable can provide reliable service for its design life. For both your new cable purchases and your 30- and 40-year-old legacy purchases if the defects are large enough the cables will fail early in their lives … these kinds of defects yield what statisticians call infant mortality.  Your decade-old cables have been screened by operation of substantive manufacturing defects – those that will actually cause a failure without an accompanying water tree. In short, manufacturing defects are everywhere, but in legacy cable their manifestation is a water tree growing from the defect. Rejuvenation directly address the water tree and Novinium Ultrinium™ 73X brand rejuvenation includes patented stress grading components, which directly address stress-enhancing defects. Click the links below to learn more about stress grading …

Title

Posted

Really Long Term Life 

March 18, 2011

Real World I – High K 

January 11, 2012

Installation Defects

Excessively tight bending radius, excessive pull force, and exterior abuse rendered during installation are analogous to manufacturing defects. Serious problems manifest themselves shortly after installation. If an installation defect survived for several decades it is not so serious that it cannot be addressed by rejuvenation technology, particularly technology that includes Novinium patented stress grading chemistry.

Physical Damage (post-installation)

Frost thrust, dig-ins, and critter attacks can occur at any time. At Novinium we have seen insect attacks and rodent attacks. Amphibians have never been a problem. In the case of critter attacks, these usually occur near terminations and hence are often discovered and rectified as a routine matter during a rejuvenation program.  Dig-ins and frost thrust are generally not discoverable, but follow a pattern similar to manufacturing and installation defects. Cables struck with significant damage fail shortly after the event, insignificant damage may be mitigated by rejuvenation. In summary, rejuvenation mitigates, but does not prevent all failures resulting from post-installation physical damage. Rejuvenation with stress grading technology such as that found in patented Novinium Ultrinium™ 73X brand rejuvenation fluids provides superior mitigation.

Testing Induced

My faithful readers know that this frog is not a devotee of diagnostic testing. The fundamental problem can be summed up thusly:  None of the technologies can reliably discriminate between cables which will fail in short order and those which will not. The rejuvenation program alternative puts a final nail in the diagnostic coffin, because components will all be changed anyway. What sense does it make to find out if the components are good or bad? Since over 99% of rejuvenated cables don’t fail when no diagnostics are utilized and the extension of life is 5-20 times longer that the retesting horizon, paying for a diagnostic is difficult to justify.  If all of that were not enough many diagnostics test induce defects! Electrical trees can be initiated directly by high voltage methods such as off-line partial discharge or indirectly by inducing space charge with DC methods. Even though it makes no technical sense to test, rejuvenation does mitigate the damage testing inflicts on cables if rejuvenation is given some time to improve the dielectric performance of the cable.  For SPR that is about a week; for UPR it is best to wait for at least a year. To explore diagnostic testing further do a key word search on my blog for “diagnostic testing.”

Insulation Shield Separation

Loss of adhesion between the insulation shield and the insulation is a rare occurrence and is the only fault mode not addressed or at least mitigated by rejuvenation. This frog can count on one front paw, and I only have four toes on that paw, the number of failures where the loss of insulation shield adhesion was the cause of failure. These few observed failures suggest that chemical contamination of the soil causes swelling of the shield material and loss of adhesion. Transformer oil or motor oil spills are suspected culprits. If you have a bunch of these kinds of failures on your hands, you have a potential Love Canal situation and you are going to be excavating the whole neighborhood.  No need to treat the cable.

Summary

Advanced cable rejuvenation provided by the masters at Novinium has a proven track record of 99.4% post-rejuvenation reliability. Almost all known causes of solid dielectric underground cable reliability problems are either directly addressed or mitigated. The sole exception is insulation shield separation, which is incredibly rare.

Broad Spectrum Reliability,

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