EPR (Part 1 of 3)
Dear Grandest of Frogs,
I was in the audience of an ICC (Insulated Conductor’s Committee) discussion group C30 (Extending the Life of Field Cables) and was confused by the discussion about treating EPR cables. There were some in the room who seemed to be of the opinion that rejuvenating EPR cables is not appropriate. Does it ever make sense to rejuvenate EPR cables?
Ethel P. Reliability
I was not at the meeting in question, but I have several very good friends who were, so I got the straight scoop. First there was a bizarre suggestion that those who originally invented rejuvenation technology never intended to treat EPR cable. Two gentlemen who were actually there for the original inventive step of modern alkoxy-silane-based rejuvenation technology were founders of Novinium and are able to confirm that claim is without merit. The target of the development effort was solid-dielectric cables – EPR cables fall within that genre. There were several very vocal proponents of EPR cable at that meeting and they were united in a common narrative. To wit, EPR cables do not fail, they do not suffer water treeing, and hence rejuvenation is counterproductive.
Poppycock! Poppycock! Poppycock! Let’s take those assertions one at a time.
EPR cables do not fail
EPR cables do fail. One laboratory (Cable Technology Laboratory or CTL) that studies cable failures on a routine basis reports that over three decades they have received about 600 samples of failed XLPE cable and about 10 samples of failed EPR cables. At first glance, one might say that this anecdote suggest a 60-fold reliability advantage for EPR cables over XLPE – that assumption would be exagerated, because about four-times more XLPE cable was deployed from 1964 to 1980 (See Forrest, “Predicting Medium Voltage Underground Power Cable Failures and Replacement Costs,” Western Electric Power Institute, Apr. 8, 1997). What would be fair to say is that over the course of the last three decades, the reliability of 1960-1980 vintage EPR was about 10 to 15 times better than the same vintages of XLPE cables. Historically more reliable, yes … invulnerable, no … in need of rehabilitation at some point, yes.
EPR cables do not suffer water treeing
It is true that imaging water trees in EPR cables is quite challenging. EPR cables are filled with clay and as a consequence even very thin samples are opaque. Traditional microscopic examination with staining often fails to reveal water trees. A colleague at CTL has figured out a way to image trees in EPR. Bogdan Frysczyn’s annotated images nearby show bow-tie and vented water trees right at the failure breakdown channels in so-called “pink” EPR. Similar images have been made for brown and black EPR too. So much for that narrative.
Rejuvenation of EPR would be counterproductive
Now that we have established that EPR cables do fail and that they suffer the same water treeing phenomenon as XLPE cables, it would seem to be self-evident that rejuvenation would benefit aging EPR cables. Over a decade ago, my friends over at CTL together with EPRI (Electric Power Research Institute) and Reliant Energy (Houston) wrote a paper demonstrating just this entitled, “Extending the Service Life of Ethylene Propylene Rubber Insulated Cables.” In this paper, the authors concluded:
It is feasible to upgrade early vintage black EPR cable and achieve a significant increase in ac and impulse voltage breakdowns.
It is feasible to upgrade current vintage pink EPR cable and achieve a significant increase in ac and impulse voltage breakdowns.
These results were based on treatment with phenylmethyldimethoxysilane (PMDMS), which is the primary ingredient in both CableCURE®/XL fluid offered by UTILX® Corporation and Perficio™ 011 fluid provided by the Masters of Reliability™ at Novinium. In two subsequent posts, this frog will explain another misconception perpetrated at the last ICC meeting (EPR 2 of 3) and how the technology has advanced over the last decade to improve the post-injection reliability of EPR cables specifically (EPR 3 of 3).
Eternally Proactively Reliable,
Thermonuclear B. Frog