High Voltage cable / LBE storage

[farmape]

What is the opinion on the long term effects of 5-25kV shielded power cables de-energized for long periods of time ... that is, cables that are "backups" or "WIP". Cables that are in underground ducts, outdoors, and run through a facility. Will keeping such cables energized be beneficial (i.e., help prevent aging / moisture infiltration) OR, will it actually decrease the cable life (from the stress of high voltage)?

Also, load break elbows (typical elastimold type). Is the outside/exterior a semi-conductive ground material? Is it NOT recomended to have these terminations energized without being landed or a dead end insert inside the elbow?

Thanks in advance, there seems to be some strong opinions on this either way, I know this site has excellent knowledge base.

 

[Zogzog]

I would keep them energized due to the transition from underground/outdoor/indoor factor. Moisture is your enemy and these are perfect conditions for moisture to ingress. Keeping them energized will ensure they are ready when you need them.

IF you decide to de-energize them for long periods of time you better be ready to do testing on them before energizing, Tan Delta would be best for detecting moisture/water trees.

What type of cable is it? Any splices?

 

[farmape]

Thanks for the advice. these are typically copper conductor , MV-90 or MV-105, copper tape shielded XLPE or EPR insulation, with a PVC jacket.

 

[ANGIBEW25]

Hi Farmape:
I agree with Zogzog it is better to keep your cables energized with no load on them. If you shut MV cables down for long periods of time you should test them before re-energizing.
The exterior surface of load break and dead break elbows is not designed with conductive or semiconductive materials. All semi-conductor surfaces are inside the load break or dead break elbow.
You should land or "park" any load break elbows in a 1-way standoff. you would need (1) stand-off per phase conductor. If you have pad mounted equipment there should be a receiver on the equipment to mount the stand-offs.
Hope this information was helpful. Good Luck.

 

[davidbeach]

Yes, yes, yes, keep them energized. Once they've been deenergized for any length of time you no longer have any knowledge of the condition of the cables.

If kept energized and they fail you will know it immediately and can get them replaced. If kept deenergized you won't find out about a cable failure until the point you really want that cable to be good.