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Dielectric II

June 20, 2012

Dielectric II

In Dielectric I, I provided the first part of a four-part answer to a query—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 Sustained Pressure Rejuvenation (SPR) there is zero additional risk. With Novinium’s improved Unsustained Pressure Rejuvenation (iUPR) process the risk is many times less than the legacy approach used by others. The legacy paradigm is called Unsustained Pressure Rejuvenation (UPR). 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 Cablecure® 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 raised in questions 6 through 8.