Moisture in Power Cable 3

[sksimonsen]

We have 2000 ft. of (3x1 conductor) 350kCmil 15kV XLPE shielded power cable that has been installed in conduit, below grade, about nine years. We believe, through failures and subsequent testing, that the cable may have moisture in it.
1) Can the moisture be removed by injecting nitrogen, under pressure, into the cable? If so, how does one go about locating someone (in the US) to do that?
2) Since there is a real possibility if water trees having formend in the cable, we have also heard of injecting liquid silicon into the cable, both to drive out the moisture and to seal the carbon path "trees". Is anyone familiar with this process?

 

[jbartos]

Suggestion: The length of the cable and how far the moisture penetrated into cable are the factors to be dealt with. The cost of such remedy and the uncertain outcome might be considered in favor of the new cable.

 

[jghrist]

1) Yes, moisture can be removed by injecting nitrogen into the cable. Sorry, I can't help on locating someone to do the job. A google search should get some results.
2) I looked into this a few years back for a project. It looked very promising, but for our application we decided that selective cable replacement was more practicable. This was in Saudi Arabia, with cables in duct. We also had disconnectible splices in all manholes that would have to have had special attention because the silicon fluid would not flow through the splices. Your situation may be different economically, being in the USA. There is much more economic incentive to use silicon injection instead of replacement for direct buried, however, because of the high relative expense for replacement. See

http://www.wiredynamix.com/index.html.

 

[BJC]

Most cable vendors will have a proceedure for removing water from the stranded conductor of a cable. They will vary sllightly from vendor to vendor but basically they use a purge with dry (oil pumped )nitrogen.
The proceedure I have used is dry nitrogen regulated at 15 to 20 PSI. The seal from nitrogen hose to cable end is usually a section of shrink tube. The dry nitrogen is forced through the cable picking up the water on the way. The process is continued untill there is no water comming out the opposite end. Water is detected with a desicant on the opposite end of the cable. The desicant is put a jar throug witch the nitrogen exits, it is changed as needed. When the desicant stops picking up water the inside of the cable is dry. The process may take several days.

Silicon injection is almost the same. A sligh pressure force the fluid down the core of the cable. It's also a slow precess. See these guys for one.

http://www.infrastrux.com/company.asp?CompanyID=8

 

[jbartos]

Suggestion: It is also necessary take into consideration losses caused by the procedure, and potentially repeated outages. If the cable is replaced, then there will not be more outages and associated losses.

 

[busbar]

There are six vendors listed in the T&D World buyer’s guide under cable-restoration services.

http://www.tdworld.com/bg.asp?codeID=172970&parentID=172788&siteID=30&magazineID=108

 

[sksimonsen]

I want to thank all of you who responded, your valuable assistance is most certainly appreciated!