Dear Wisest Webbed one,
I am working on my comments/concerns for the Safety Section for the C30 Draft Guide [Editors note: C30 is a group within the IEEE/PES/ICC working towards the writing of a “Draft Guide for Rehabilitation and Rejuvenation of Extruded Dielectric Cable Rated 2.5 kV through 46 kV.” While that Draft is being crafted, interested readers may wish to review a Novinium published early version undertaken at the behest of the group’s chair, which is available at www.novinium.com/Standards.aspx.], and have a few questions. Just because the equipment is all or mostly plastic materials, these questions still need to be explored and discussed.
- What is the insulation rating of the fluid(s) that you use for injecting?
- What is the insulation rating of the hose(s) you use from your canisters to the injection point?
- What is the insulation rating of the canisters themselves?
- What is the insulation rating for the combination elbow/canister?
- Do you have the test data for these pieces of equipment? Will you share the test data with the group?
- Have you looked at the electrical separation distance from your canisters to the cover or live bushing?
- Have you looked at the electrical separation distance from your canisters to ground wires in the equipment?
- Have you looked at the electrical separation distances from your canister connected to one phase and to the other phases in a three phase installation?
Your froguidance would be appreciated.
Alabama detailed draft
I don’t know about you, but the fact that the first three letters in dielectric spell “die” makes me want to take extra measure to assure the safety of all who use dielectric enhancement technology. The heart of your eight questions can be summarized thusly: To what extent does the introduction of injection equipment into energized devices impact the safe operation of medium voltage circuits? Before I answer that question generally and some of your more specific questions, it is important to recognize that there are three distinct methods of dielectric enhancement fluid injection and two conductor realms in which those methods are deployed. Ordered from oldest to most advanced, the three methods are:
UPR ♦ Unsustained Pressure Rejuvenation,
iUPR ♦ improved Unsustained Pressure Rejuvenation, and
SPR ♦ Sustained Pressure Rejuvenation.
To learn more about the details of these rejuvenation methods, check out my June 18, 2010 post titled “How to Inject.” Novinium is synonymous with safety, so we use the two most advanced processes almost exclusively. In the very unusual cases where Novinium leaves injection devices attached to energized devices for more than a couple of days, equipment designed specifically for that case is deployed. Because it is a rare case, I refer interested readers to my April 15, 2001 post, “Soaking II: Safety First” for more details.
In this series of posts, I focus on the cases most important to circuit owners. In the table nearby the implementation of the three injection methods are compared for the two conductor cases, namely small conductor and large conductor. Small conductors include stranded conductors, generally with 19 or fewer strands. Note that for large conductors, cables are injected de-energized whichever injection method is utilized, and hence your questions are moot for these large conductors. Further, SPR is applied over 99% of the time to deenergized cables, and hence the questions are again largely moot. The only firm in the world that can deliver iUPR and SPR is Novinium, because we own the intellectual property on the methods and chemistry that make those processes possible. For most injection work we undertake, we operate in the green … my favorite color.
When we do inject into energized devices we mitigate the risks about which you are inquiring by limiting the period that injection equipment is connected to energized components. In the red portion of the table, older technology requires extensive soak periods spanning several months. At first glance you might assume that reducing the period of time by sixty-fold would reduce the exposure to the risk by sixty-fold, but you would be underestimating the impact. In the iUPR process, fluid flows in only one direction. A feed bottle with a positive pressure, typically about 20 psig, is attached to one cable end and a vacuum bottle with a negative pressure of around -10 psig is attached to the other cable end. Fluid flows from high to low pressure. Both the feed tank and the vacuum tank are removed concurrently. Thus on the feed side, fluid with a high dielectric strength flows through tubing made of a high dielectric polymer and there is a negligible probability of substantive current flow. I’ll provide some data in my second post, Dielectric II. With iUPR the only substantive design issue is on the vacuum or outlet side, there is no way to be certain what will come out of the outlet, so we have to assume that it will be water. In practice, water seldom comes out of 7-strand or 19-strand cables (To learn why, click here.), but from a design perspective this is the worst-case assumption.
UPR has the same worst-case on the outlet end, but it also suffers from a more insidious issue on the inlet end. I examined this issue in some detail in my April 15, 2011 post, “Soaking II: Safety First.” You should read that post, but in summary, UPR suffers a risk that conductive contaminants will render the feed fluid conductive. The worst-case assumption on the inlet side is about the same as the on the vacuum side, but the feed is connected for 60 days or more. This risk is recognized by the practitioners of UPR, because they explain the risk and a potential solution to mitigate the risk in U.S. Patent 7,704,087 of April 27, 2010. Amazingly after exposing the risk those practitioners have not implemented their mitigation strategy. I usually speak only of technical matters, but you don’t have to have a law degree to recognize that if you know about a safety problem, but do nothing to mitigate the issue – your liability undoubtedly increases. Risk managers should take this knowledge into account as they make their choice between the various injection processes. If your firm believes in safety as the most important criteria, don’t utilize UPR.
In my next post (Dielectric II), I will provide some data to show why the feed end of an iUPR injection is not a safety issue. 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 you raise in your questions, 6 through 8. For a thorough description of all of the rejuvenation dimensions of safety check out the 89-page treatise, “A Comparison of Rejuvenation Hazards & Compatibility.”
Practicing safe rejuvenation,
T. B. Frog