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Flowing Through Splices

September 2, 2011

Flowing Through Splices

Q:

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?A:

“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.[dt_fancy_image type=”image” image=”http://www.novinium.com/wp-content/uploads/2015/08/Interface-tracking-sans-background.png” image_alt=”Interfacial tracking is one of the reliability risks eliminated when splices are replaced.” style=”2″ width=”600″ padding=”10″ margin_top=”0″ margin_bottom=”0″ margin_left=”0″ margin_right=”0″ align=”center” animation=”none”]Interfacial tracking is one of the reliability risks eliminated when splices are replaced.

Category Considerations
Okay Modern molded EPDM or EPR If splice was installed with good craftsmanship it should provide reliable service. Some portion of the fluid intended for the cable is absorbed in the splice.
Bad Ancient molded splices Old technology may not meet modern reliability standards.
pin & socket splices Generally don’t flow; when they do flow, prone to leakage.
Heat shrink Generally don’t flow.
Non-silicone cold shrink
Splices for cables larger than 4/0 (95 mm2) Cannot hold enough pressure to support flow without leakage.
Ugly Splices made of silicone rubber Silicone may swell from treatment fluid and fail.

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., I don’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.