Water in Cable

[nickoliver]

I am doing a small power plant and a ran into a problem yesterday. When terminating the last run from the generators to the paralleling gear we found water ingress in one of the cables. The run is a 4" conduit with 8 350MCM XHHW conductors (+ ground). Operating voltage is 480/277. Part of the run is underground, part overhead. Out of all the runs from all the generators this one cable is the only one with water. The end with the water is at overhead portion of the run and after it was stripped back there was a slow drip coming from it. It sat coiled up in dry switchgear for more than 6 months before we went to terminate it yesterday.
My question is on a <600V system how much of a concern is this? We are replacing the entire run but I am wondering what the potential consequences could be if it were left like this. I realize in medium voltage applications this is disastrous but in this case if we purged the cable with nitrogen would it be OK or would cable life be considerably shortened?

 

[BJC]

Call the cable vendor. Most have instructions for drying out the inside of cable. The technique is to hook up a bottle of dry air or nitrogen at one end. Using a regulator you purge the cable for a time by letting the air flow through the cable. The vendor will give the details on time, pressure and the indicator to use. Try the local utility as well. Most utilites have the process in their standards. Don't leave it the cable, it turns to steam and could damage the cable.

 

[alehman]

Water may also lead to corrosion of the copper and terminations. Another reason to dry it. Is it possible the water got in prior to installation? If not, you need to find out where the water is coming from.

 

[nickoliver]

Thanks for the replies.
We pulled all the old cable out today and the conduit was dry. The only explanation is that the water was there when delivered to the site. All new cable goes in Wednesday. The owner did not want to try purging.

 

[weh3]

Stored cables should be sealed at the ends, but water does get into cable. Normally, the heat from an operating cable keeps it out, which is why a cable can operate for years without a problem, but fail on restart after it cools and condenses. Put a small load on it for a while to dry it out before putting full load on it. As long as the insulation is intact, it should be OK.

William