Medium Voltage Cable Insulation/Jacket Tracking

[richanton]

My building has 13.8kv feeders that come in underground thru manholes. We opened up one and saw some dark discoloration that appears to be not only on the cable, but on the metal cable support. Has anyone seen anything like this. Is this a "tracking" issue. All grounds are good and there have not been any failures in the past. The cable is about 20 years old. It's an Okonite 133% EPR cable I believe. I attached a photo if the upload worked.

 

[richanton]

I uploaded the .jpg photo to engineering .com as suggested, but I don't know how anyone can access it.

 

[richanton]

Ok, I think I have this now. Link to photo should be below.

 

[Zogzog]

Have you tested it? Which method and what were the results?

 

[7anoter4]

In my opinion, the cables-may be it is a triplex-are wrapped in an insulated band and the manhole was filled by water[rain water] and the white color it is the sign remained from water [some chalk or lime dissolved in the water].

 

[richanton]

We haven't tested anything yet. We are trying to determine if testing is where we should go next. I think the idea that the discoloring could be due to rainwater may be feasible. I'll post here later with results if we do decide to test the cable.

 

[jghrist]

The wrapping is probably fire-proofing tape. I agree with 7anoter4 that the discoloration is probably caused by water. It's also possible that the discoloration was caused by a fault in another cable that has been replaced. If it were caused by arcing of the cable, the cable would not be in service. Faults on MV cables are not temporary, they don't self clear.

 

[dpmac]

Looks normal to me. Water, silt residue, minerals associated with the fire wrap as others have mentioned.
If your really concerned, remove a section of fire wrap and take a look at the cable itself. Should be fine.