Drying out moisture in EHV cables 1

[aslamajec123]

In one of my 10km long , 400kV Lead sheathed XLPE insulated Power Cable installation project, contractor had completed few cable joints up to copper casing but he could not provide final water proofing compound and coffin box since supply of the same was awaited. During this stage there was heavy rain and these joints got flooded. Later after 6 months these joints were opened to investigate the ingress of water.when copper casing was opened silicon carbide powder was found wet but the cable joint itself inside premould joint body was found dry. However moisture was found entered in to cable layers at the end of joints under soldered area between copper casing and lead sheath.It was observed that water swelling tapes below lead sheath and above insulation semiconductive screen was wet.
I am concerned that the semiconductive insulation screen below water swelling tape might have absorbed water and moisture could reach XLPE insulation and possibly absorbed in such case there my potential formation of water treeing in XLPE insulation in future during its operation resulting in to failure of cable.
considering the importance of 400kV system , I did not wanted to take any sort of risk and preferred to replace all the affected cable sections with new.
However Cable manufacturer/contractor propose to heat the cable and dry the moisture by vacuuming.He is not expecting moisture to penetrate more than one meter in the cable as water swellable tapes will restrict the propagation of water .I am not sure how reliable is this process of drying out the moisture and how can I be sure that if all the moisture has been dried out. It is not possible to cut the cable and test in laboratory to verify the dryness of the cable layers as this will shorten the length of the cable and contractor will not be able to install new cable joint.
Further I am not sure if the above drying procedure will remove the moisture from Semiconductive screen and XLPE insulation if it was absorbed.Also it s it possible that during heating of the cable of the moisture can turn in to vapor and penetrate further deep in to other side of the cable rather than escaping out from the open end of the cable.
Can you kindly give your openion if it is 100 percent reliable to go for drying the cable by heating and vacuuming the cable or purging it with dry nitrogen. How can I make sure after the above drying procedure, there is no more moisture is present in any layers of the cable and monitored has not penetrated deeper.Does any engineering standard support the above procedure of drying the power cables ? Or is it recommended to replace the complete lengths of the cables ? Client do not prefer including additional joints as same are considered as weak points for the failures and in such case complete section of cable of length 500 meters each may required to be replaced at affected 7 cable joints .

 

[waross]

Call your lawyer.
If the Cable manufacturer/contractor is willing to sign an extended warranty assuming full financial responsibility for the full cost of repairs to any future failures, including specified* damages for loss of revenue and any other business losses, then consider letting them go for it.
You may also want to have your insurance underwriter involved.
You may also ask for assurances that their insurance underwriter will cover all costs in the event of a future failure.
They screwed up.
It is their responsibility.
Make them assume any future risk involved in drying the cables.

Specify the specific amount of damages in the event of a cable failure. Don't let the judge decide the amount nor lawyers argue about the amount of damages while you pay them by the hour.

Bill
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"Why not the best?"
Jimmy Carter

 

[7anoter4]

In my opinion, the contractor has to dry the cable by nitrogen purging and test the cable according to recommended BIL and I agree with waross : from this date he has to start a new warranty. Lower voltage cable [as medium voltage cable] could be treated by heating in order to dry it.

 

[aslamajec123]

How effective is drying the power cable with nitrogen purging? Can it confirm life of the cable Same as new cable after this process of drying ? How many years it may take to form form electrical tree and breakdown the insulation if moisture is retained within the insulation?

 

[HamburgerHelper]

I have no experience with this but my gut tells me that it will be like a car that has been in an accident. Some things never be right and you'll be blamed if something happens even if it is just coincidental. I suppose it depends on what kind of a deal they give you and what kind of reliability you need.

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