138 kv underground lines


Old 05-03-06, 08:33 PM
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Join Date: Oct 2005
Location: Milwaukee WI
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138 kv underground lines

Not exactly a DIY issue, I am just looking for a resource or pointer.

I was out on a bike ride earlier (beautiful day today) and ran across a spot where one of the overhead 138KV lines goes underground to feed my local substation. I was doing a little googling and found out about this HPGF/HPFF cable http://www.okonite.com/paper-cable.html and a story about installation of such a line underwater and so on.

But I am more interested in how this operates, which I couldn't find any info about. For example presumably there's a compressor-chiller station at the substation and it pushes chilled gas or liquid through the cable - but what happens at the far end? Is there a refrigerant loop in the cable or what? What kind of tonnage is required?

There's just a box about 2x2 feet in the overhead terminus where the UG cable comes up, but there is a large building at the substation that has fans and noise beyond the usual substation hum.

Thanks for any info or pointers.
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Old 05-03-06, 08:41 PM
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Perhaps the cooling is thru Nitrogen, and the fans are cooling the transformers.
Old 05-04-06, 07:22 AM
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The buried cables are pressurised with gas or liquid ( oil). Both ends of the cable have pressure sensors on them. When the cable pressure drops, it generates an alarm so that the electrical company knows that there is a problem with the cable. A slow pressure drop indicates that there is corrosion in the cable and that the insulated value of the cable is no longer good and need to be fixed.

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