Dielectric II

In Dielectric I, I provided the first part of a four-part answer to a query from Alabama – the summary question: To what extent does the introduction of injection equipment into energized devices impact the safe operation of medium voltage circuits? We learned that there are great differences in the extent of this risk depending upon the injection paradigm employed. In fact there are three injection paradigms and at Novinium we use only the safest processes. With Novinium’s patented SPR (sustained pressure rejuvenation) there is zero additional risk. With Novinium’s iUPR (improved unsustained pressure rejuvenation) process the risk is many times less than the legacy approach used by others. The legacy paradigm is called UPR (unsustained pressure rejuvenation). In this post I provide data to show why the feed end of an iUPR injection is not a safety issue – unfortunately the same conclusion is not true for the legacy UPR process.

In the illustration nearby I am standing next to iUPR injection equipment. From left to right are …

A CO₂ cylinder enclosed in a PVC bag provides energy to urge fluid into the cable strands.  A polyethylene CO₂ supply tube provides about 20 psig of pressure to the predominantly plastic feed tank. At least three feet of polyethylene fluid supply tube with a wall thickness of 100 mils delivers fluid to an injection adapter and a mated injection elbow. In another case not illustrated, the fluid might be supplied to a live-front injection adapter. Whether dead-front or live-front, the fluid comes in direct contact with an energized conductor. The fluid is a dielectric, and with Novinium’s improved unsustained pressure rejuvenation process, the flow is one way – toward the termination. This one-way flow provides assurance that there is no fluid contamination from backward flow as suffered by legacy approaches. At Cable Technology Labs (CTL) the leakage current in a column of Ultrinium™ 732/40 fluid was measured between two electrodes at 15, 25, and 35 kV. The leakage current was steady at about 0.03 mA, 0.04 mA, and 0.05 mA for 15, 25, and 35 kV respectively from 14 feet of electrode separation down to less than 1 foot.

With the Novinium iUPR process there are no ground electrodes ever in direct contact with the fluid. The fluid flows though several feet of PE tubing with a wall thickness of 100 mils. The AC breakdown strength of the PE is at least 800 volts/mil and hence the AC breakdown strength of the tubing is greater than 80 kV. The fluid flows from a polypropylene/acetal tank with even thicker walls than the tubing. The closest ground plane is typically the concrete or earth on which the feed tank rests. Novinium has deployed these iUPR systems thousands and thousands of times and there have been zero issues. We wrap the CO₂ cylinder in a PVC bag to prevent accidental contact with exposed secondary voltages.

In my third post in the series, Dielectric III, I will discuss the design issues of the vacuum tank designed for iUPR and the features that make iUPR the second safest injection approach. Finally, in Dielectric IV, I will address the equipment separation issues Alabama raises in his questions, 6 through 8.

Dielectrically delighted,

T. B. Frog

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