Medium Voltage Cable stored in Wet Conditions

[Donh]

I have a Contractor who installed 15KV EPR cable through a series of manholes starting back on 12/22/04. There has been numerous delays in this project and the cable still has not been energized. I can't find anything in NEC that addresses this issue. The cable has been spliced in most manholes, however in 3 locations it's just got a heat shrink end cap.

[ January 12, 2006, 08:21 AM: Message edited by: Donh ]

 

[bdarnell]

Re: Medium Voltage Cable stored in Wet Conditions

We install a lot of medium voltage underground cable from 15kV up to 35kV, I secured some of the heat shrink end caps that you mention and we are diligent about putting these on as soon as the cable is cut from the reel. Never had any moisture problems so far. But, we never install cable or splice during inclement weather, and we never store our cable outdoors for a lot of reasons. Not the least of which is the potential for vandalism. All it takes is a finish nail driven through the cable and you get to test your fault interrupters.

Your mileage may vary. Good luck.

 

[don_resqcapt19]

Re: Medium Voltage Cable stored in Wet Conditions

I don't see any problem. It is in almost the same conditions as when it will be energized. The caps should provide the same protection as a splice or termination. Just have it hi-potted before it is energized to make sure.
Don

 

[celtic]

Re: Medium Voltage Cable stored in Wet Conditions

I also don't see an issue.
The cable has been "terminated" to prevent moisture from entered the end.

Before energizing the cable, proper testing should be performed by qualified people.
If it would make you feel any better (and you are willing to spend the cash) have them tested now.

 

[zog]

Re: Medium Voltage Cable stored in Wet Conditions

"Before energizing the cable, proper testing should be performed by qualified people"

Make sure they are qualified, there is alot more to cable testing than most people are aware of, the latest tescnology is VLF testing, which is a low hZ AC overpotential test that is not nearly as destructive as DC testing. I recommend you find a NETA testing firm to test your cable before you energize. www.netaworld.org lists firms in your area.

 

[Nick]

Re: Medium Voltage Cable stored in Wet Conditions

As said already as long as the ends were properly sealed it should be ok. But if you think there may be moisture in the cable it can be purged with nitrogen. I am sure at least a few of the contractor in Zog's link have this capability.

 

[celtic]

Re: Medium Voltage Cable stored in Wet Conditions

Originally posted by Nick:
...But if you think there may be moisture in the cable it can be purged with nitrogen. .

That must be quite a trick getting the gas in there:

Okonite

 

[zog]

Re: Medium Voltage Cable stored in Wet Conditions

A 3ft pipe is placed over the end of the cable, sealed, and attached to a nitrogen bottle, about 8psi or so is used to slowly purge the nitrogen over several days.

 

[rick hart]

Re: Medium Voltage Cable stored in Wet Conditions

On a project like this, there should be acceptance testing done before energizing. After waiting 2-3 years, you should insist that the cable is like new. The Hi-pot test will certainly reveal a fault but, I would recommend less distructive testing for the conductors. Depending on the lengths, power factor testing will show if moisture has compromised the insulation and give you a baseline for future testing.

 

[benlanz]

Rick Hart,

I agree that an acceptance test should be performed on new extruded cable installations. However, if you are referring to a DC Hi-pot test, IEEE 400-2001 no longer supports this type of test. Again a nondestructive test is the right idea but, a power factor test is nearly useless on a new shield medium voltage cable installation. IEEE 400 recommends repeating the cable and accessory manufacturers' partial discharge diagnostic test in the field.


Kind regards,