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Why does the load matter?

February 24, 2011

Q:

Why are the folks at Novinium so insistent on knowing the loading of my feeder cables? This guy named Steve keeps asking me to estimate the load growth. How am I supposed to do that? Is this effort really worth it? Your NRI20 [Novinium Rejuvenation Instruction 20, Tailored Formulation™ & Tailored Pressure™] step 3 requires that I categorize the load into low, moderate or heavy. How do I do that?

A:

Temperature is really important! Let’s start with a four-step chain of causality…

Chain of causality

1. Load affects temperature. (The cable warms as more current flows.)

2. Temperature affects the permeation rate of rejuvenation fluids. (Permeation rates for all treatment fluids increase by about a factor of three for each 10°C temperature increase.)

3. Permeation rate affects how quickly rejuvenation fluid exudes from the cable. (The faster fluid permeates through polyethylene, the faster it can sweat out of the cable.)

4. Rejuvenation fluid exudation affects the treatment life extension. (If the fluid leaves the cable, it isn’t helping it!)

Only Novinium’s patented approach of tailored formulation™ (U.S. Patent 7,611,748) is able to adjust the formulation and quantity of the rejuvenation fluid supplied to mitigate the aforementioned pernicious chain of causality. That may be why the other guys don’t bother to ask.

Would you like to maximize the life extension your circuits enjoy? I presume your answer is, “Yes!” Tailoring the formulation requires just a few pieces of data. I’ll bet they are fairly easy to come by.

1. We already know where you are, so we can use the global soil regime map nearby to estimate the soil temperature at cable depth. A larger version of the map is also at the aforementioned NRI. For Ohio the soil is mesic and the temperature at cable burial depth varies from 8 to 15°C.

2. Based upon your local soil thermal conductivity, provide me with the maximum design load and the corresponding temperature. In the example that follows these values are 603 amperes and 90°C respectively.

3. Download some historical load data for the circuit. The data should have a date and time and load in amperes. The data should be at least every 6 hours over a one year period, each one hour is even better. That’s a lot of numbers, but computers excel at this and we have a MS Excel worksheet that makes child’s play of the number crunching.  We then convert the load values to approximate temperatures as shown for example in the nearby graph titled, “Current-Temp Relationship.” In another nearby graph titled, “Flux Weighted Temperature Estimate,” four days of data are shown for the example circuit. The historical flux weighted temperature (FWT) is thus calculated.

4. Next you need to estimate your anticipated annual load growth over the period of the circuit’s remaining life. Don’t let the perfect be the enemy of the good. Of course, you can’t know precisely what the future load growth is going to be, but your planning process should generate a better estimate than me sitting on a lily pad 1,933 miles away. For this example, the annual load growth is 1.2% and the circuit owner desires 40 years of additional life.

Based upon the Novinium technology embodied in a pair of U.S. Patents titled, “Predicting Performance of Electrical Power Cables,” (U.S. Patents 7,643,977 and 7,848,912) Novinium estimates the prospective FWT. For our example, the historical FWT is about 15°C and the prospective FWT is 26°C. The appropriate fluid choice is Ultrinium™732/30. This cable has a low load.

P.S. At least one of my readers is undoubtedly wondering: What the heck is Flux Weighted Temperature? Click on the link to learn more.