Water in Neutrals of MV Cable - Reason for Concern?

[FEinTX]

I posted earlier this week about sheath testing on a 34.5 kV collection system and with the information I got here coupled with some information from the cable supplier, I now know why our EPC is failing these tests. Basically, (1) they were testing the sheath at too high of a voltage level (10 kV instead of 4.6 kV) and (2) they were being too rough w/ the cable during installation inflicting nicks and small cuts in the jacket that were not inconsequential as was thought. Going forward, I think we are in good shape--they are using a new installation process and the sheath tests will be done at a much lower voltage.

But what about the cable that's already in the ground?

We have observed numerous small holes w/ burn marks from the 10 kV megger tests in the cables we've checked. Obviously, the jacket can no longer be watertight at these locations, but the engineer from the cable company says this is OK. He says the purpose of the jacket is to mechanically protect the neutral and to hold it tight against the semicon. He claims that corrosion in these areas will not harm the semicon and that you'd only get into trouble if you had an area 20-30' in length where a voltage gradient could reach levels high enough to arc.

Do we have any MV cable experts out there? Is a waterproof jacket necessary? Why or why not?

Related - These are end-bonded/grounded runs, so I don't believe intermediate ground points will cause a problem electrically like they would on a cross-bonded or single-point bonded run. (Let me know if you see a problem w/ this statement...)

Thanks,

FEinTX

 

[SphincterBoy]

I think waterproofing is important. We've had to replace much of our URD cables, due to water trees. And after going out a few times with the lads, and hearing homeowners complain about our trenching trying to dig up the location of failures, we do everything we can to get stop water from getting to the cable.

We've been spec'ing Pirelli SuperDri cable, to keep water from ingressing into the cable, once the integrity of the sheath has been broken. Water will eventually corrode the neutral conductor, if it isn't protected by a jacket.