Medium voltage cable

[SplicerB]

My first post .... I have some 15 kv cable that was pulled on my job the ends were sealed with heat shrink caps. My splicer went a couple of weeks later and cut and racked the cables to remove excess cable and prepare for pull from other direction. Two weeks past and I sent a crew to clean out hole and prepare for pulls to discover that the mh had 7 feet of water in hole from only a half inch of rain. I had crew sump out mh and clean out mud to discover that the cable ends had not been resealed by splicer with heat shrink caps. The cables were not saturated but have moisture that has drained for ten days . I am pretty sure I know the answer but would appreciate any input on how to properly handle this.

 

[Jraef]

Read the section entitled "Cable and wire require closer consideration" in the following article:

http://ecmweb.com/test-amp-measurement/testing-flood-damaged-electrical-equipment

In my area, the local PoCo had this happen to a LOT of MV cable in underground feeds (similar circumstances in that they installed them and failed to seal them before the rainy season). They went the silicone injection route and 6-7 years later, discovered it basically didn't really work.

 

[don_resqcapt19]

A number of years ago, we removed a 5kV service that had been in use for years. The run from the outside termination to the utility service drop had about 30' drop and a total length of about 100'. The bare ends of the conductors were pointed up and terminated with the "acorn" type of clamps at the utility connection. The load end was connected to the switch gear bus bars and the connections between the conductors and the bus were completely taped up. When we removed the tape, about a quart of water ran out of each of the conductors. It never caused any problem. The water was in the small spaces between the conductor strands and under the dielectric. This was an old enough installation that the conductors were not of the shielded type.

 

[mkgrady]

I have seen this issue many times but have never seen a problem as a result. It can't be good for the cable but it might not cause a failure if everything else is done correctly. You could pump some nitrogen through the cable to remove the moisture. I would contact the cable manufacturer to see what they require in order to o
Honor the warranty

 

[ATSman]

I will give my 2 cents and try to be brief. About 35 yrs ago working for a testing co I had the job to purge 12Kv cables with N in a mh at an airport. The distance between mh was considerable. We made up a manifold using rubber tubing, Scotch 33, pressure gauge and large alligator clip boots to connect the ends of the cables to the tanks of N. The job took 2 to 3 wks periodically checking tank pressure, connections for leaks, replacing tanks and meggering (5KV) until we got what we considered good readings. As I recall the results were successful and the installation has been fault free today.
My thought is that even if there is contamination left inside the cable after the moisture is removed and the outer sheath is not damaged then the normal life of the cable will not be compromised.
I did not see where the cable length was mentioned but you need to compare the length of the run/cost to replace with the cost of the purge procedure.

 

[big john]

The most immediate problem I see coming from this is water wicking through the termination kit and causing a failure due to insulation bridging. I have seen this happen a couple of times, and it is correctable simply by cutting the cable back and reterminating it, but if the water isn't removed from the cable, the failure will eventually reoccur. And of course this is only an option if the slack is available to begin with.

In the long haul, you'll probably get accelerated treeing that will shorten the life of the cable, but I can't speak for what time frame that damage might occur in.

Considering these are new and haven't been energized yet, I think your insulation would still be fine, and I agree that dry nitrogen purging should effectively correct it. I would want a VLF hipot or tan-delta test done on those cables prior to putting them in service, however.

 

[ATSman]

The most immediate problem I see coming from this is water wicking through the termination kit and causing a failure due to insulation bridging. I have seen this happen a couple of times, and it is correctable simply by cutting the cable back and reterminating it, but if the water isn't removed from the cable, the failure will eventually reoccur. And of course this is only an option if the slack is available to begin with.

In the long haul, you'll probably get accelerated treeing that will shorten the life of the cable, but I can't speak for what time frame that damage might occur in.

Considering these are new and haven't been energized yet, I think your insulation would still be fine, and I agree that dry nitrogen purging should effectively correct it. I would want a VLF hipot or tan-delta test done on those cables prior to putting them in service, however.

Big John
I would have to agree with the testing (I forgot to mention) in your your last sentence.

 

[zog]

I agree, N2 purge followed by a good test (TD or VLF, not just DC hipot).

 

[don_resqcapt19]

I agree, N2 purge followed by a good test (TD or VLF, not just DC hipot).

Would any of those tests tell you that you have water that entered the cable from an end where there is no treeing or other type if insulation issue?

 

[big john]

Would any of those tests tell you that you have water that entered the cable from an end where there is no treeing or other type if insulation issue?

Water will definitely lower the power factor of the cable, so you'd see it with a tan delta test compared to a known good cable.