HV cable

[isloh]

Hello everyone. I am new to the forum.

I would like to ask for help regarding HV cables.

I am sizing a cable for the secondary side of a transformer, 12MVA 4.16/138kV. I searched cable manufacturers catalogue for HV cable sizes (145kV) and found that the minimum size I can find is around 400-500mm2.
Is there a minimum size of cable that should be used for HV installation?
The current in the secondary side of the transformer is only 50.2A? Should I use 400m2 even with only 50.2A? (not taking voltage drop into consideration)

Thank you very much.

 

[davidbeach]

The higher the voltage the larger the minimum conductor size. I have no feel for mm2 conductor sizes, but I'd expect that the smallest 145kV cable would be good for 400A +/-.

 

[ScottyUK]

400mm² is a fair-sized cable, should be good for between 700A and 1000A in depending on installation method. Brugg definitely make 240mm² cable for that voltage level, I'd be surprised if their competitors don't also have something smaller than 400mm².

David - 240mm² is roughly 500kcmil. A 2:1 conversion ratio is near enough for rule-of-thumb work.

 

[davidbeach]

Thanks, I'll try to remember that. I now live in the world of 5A and 69V (or 120V), all on the secondary side of the instrument transformers.

Once upon a time I could recite the base amperages of all sorts of AWG/kcmil sizes, but now none of that matter. NESC rules rather than NEC rules, and ratings are all in the realm of the planner, not the protection engineer; besides, the conductor size may not matter at all if something else is the limiting component of the the element.

That aside, the point remains that you probably won't find a 60A, 145kV cable. 240mm[sup]2[/sup] would be in the 400A ballpark previously mentioned if it's around 500kcmil.

 

[isloh]

Thank you very much for all the replies.

I was worried that I might size the cable to big for the current it would carry. So is it is safe to say that for HV (138kV) installation the minimum size cable available would be around 240mm2 or 500kcmil?

Your help is very much appreciated.

 

[LDKGR]

Hi isloh,

did you check the cable size according to short circuit withstand ?

 

[bacon4life]

The
[link Kerite catalog]

http://www.kerite.com/Portals/0/HighVoltage/MU038_KRT_HighVoltage-catalog-lowres.pdf

[/url] lists the minimum cable size for a variety of voltages, with their minimum at 138 kV of 500 kcmil @ 529 amps.