Effect of conductor orientation on transmission line ampacity

[MrBuggy]

Hi guys,

I was playing around with conductor configurations and observed this phenomenon. Mind you these are for the High voltage transmission (138 kV) lines that span kms. So apparently, the orientation of the conductor relative to North will change the ampacity of the transmission line. Can anyone explain to me why this is the case? I mean it makes sense to me how the wind, elevation, latitude and etc. would affect ampacity as it tells us the sag, and how the sun hits the conductor.

Thanks,
MrBuggy

 

[psparky]

Hmmmm...good question. Here's a random, somewhat educated guess:

I know there some giant magnetic field in regards to the Earth. Also being parallel with the poles (north) as opposed to being perpendiclar to poles (East, West) must have some effect on the wire.

If there is some rotating magnetic field from the poles or somewhere else, that can increase or decrease current flow.
Now someone really smart can answer:)

 

[AlephZero]

The line direction determines, in part, the amount of solar radiation received by a given conductor. It is used to
calculate the angle of incidence of solar radiation. EDSA provides two choices for line direction: north-south
and east-west. Line direction is normally a parameter of little interest. If you use a sun time of noon for your conductor evaluations, you will find that an assumed East-West orientation will yield a slightly more conservative result than an assumed North-South orientation. If you use an other sun time between 10 A.M. and 2 P.M., an
assumed East-West orientation will yield a slightly more conservative rating unless your latitude exceeds
roughly 55 degrees north, where an assumed North-South orientation becomes slightly more conservative.
Obviously, if you select ‘Night’ as your sun time, it makes no difference what you select for line direction.

http://www.poweranalytics.com/designbase/pdf/Bare_Wire_Sizing.pdf page 12.

For example when the sun is due south, an E-W line "sees" more sunlight per unit length of line than a N-S line, unless the sun is directly overhead.

 

[psparky]

Or it could have absolutely nothing to do with the magnetic field and everything to do with the angle of the sun.
Missed it by that much...

 

[sophiecentaur]

At 1kW/sqm, there's a lot of power falling on a long line; makes you think. That's another thing I just learned on PF.