Suitable for Treatment
We’ve taken some photographs of cable samples identified with off-line PD testing. I was hoping to get your opinion of the cable and if injection would be able to address these issues.
- On two samples, we found the XLP insulation was a greenish color. We’ve never found cables discolored before and it had an odd odor. Upon wafering and dying the sample, quite a few trees were found.
- On three samples, we found spots where a hole was burned through the semi-con layer and dirt had gotten between the semi-con and insulation, causing some deep pitting.
I’ve attached some photos of the issues. Neither of these cables has been treated, but can they? Let me know what you think.
First off—green is a lovely color and you should be proud of your sample’s hue. The green color proves that the insulation compound manufacturer included anti-oxidants in its formulation and is generally an indication of recent heat exposure. The sulfur-based anti-oxidants break into by-products as they do their job. Some of these by-products absorb red light, leaving a predominantly yellow to green hue. The insulation may by 4201 made by Union Carbide, now Dow Wire & Cable. Click here to check out a fact sheet put out by the Dow folks called:
Color Indicates Presence of Antioxidants in XLPE Insulation Compounds
With regard to the odor, I can’t answer definitively without a sample. I can, however, speculate. The sulfur-containing anti-oxidant by-products are called thiols or mercaptans and have strong garlic-like odor. I have a cat at my house with an exceptionally keen nose. If you send me a stinky sample I can ask her to identify the chemistry involved. I hope it does not smell like tuna fish—she might gnaw on it. See “rats” below.
With regard to the water trees, you will find those in every solid dielectric cable. Water trees are the predominant cause of solid dielectric cable failure. Fortunately, Novinium provides fluids that can reverse the damage caused by water trees and replace the anti-oxidants that have been consumed over decades of field aging.
- Click here to learn how you can know that water trees are the predominant cause of cable failures.
- Click here to learn how you can be confident that rejuvenation will reverse the damage caused by water trees.
- Click here to learn how Novinium®-brand Cablecure 732/733 [Ultrinium™] fluid can replenish the anti-oxidants in aged cable.
I don’t know if the cable with the holes in it smelled like garlic, but the rodents that chewed on it must have liked the odor. I doubt that the meal was satisfying. Shreds of polyethylene would end up in her belly. I suspect the rat stopped chewing when she started to feel a tingling in her mouth – those were partial discharges. Persistence would have led to an untimely end.
Here is a question for you. How many cables had to be examined to find these rodent bites? If rodent damage is rampant in your service territory, off-line partial discharge testing might be a useful tool to find where the rats reside. It is true, that rejuvenation cannot address rodent damage, but how prevalent is this failure mode? For some insight on that question check out my three-part postings of January 2012 …
The Novinium masters of reliability have been involved in the injection of many millions of cable feet. Cables with water trees, with or without interesting color and odor, are handled easily and these represent the lion’s share of the root causes of cable failure. Add in component issues addressed by rejuvenation and a tiny minority of potential issues are left unaddressed. It is for this reason that more than 99.4% of all cable treated by Novinium enjoy failure-free reliability.