RAIL Conductor ACSR Problem

As always, you must read the fine print in the footnotes where it states:

(*) Note: The values of current rating mentioned in above Table are based on wind velocity of 0.6 metre/second, solar heat radiation of 1200 watt/metre² , ambient temperature of 50ºC & conductor temperature of 80ºC.

Yes, it's called "derating" for the ambient conditions. The conditions in the desert represent a much higher solar insolation (1,200 vs 1,000 W/m²), a much higher ambient (50 vs. 20ºC), and a much higher conductor temperature (80 vs. 50ºC), all of which contribute to approximately 33% derating factor (680 vs. 960A).

You can of course ignore the realities of the situation and push 960A through the conductor, but the 50% increase in current will result in a 125% increase in the amount of losses that go into heating the conductor. The result will be an even hotter conductor that has greater sag, more annealing, and shorter life.

To its credit, Oman Cables understands the usual conditions where its cables are deployed, and acts in a responsible manner by rating them accordingly in an effort to prevent the situation that you are trying to force.

Ethical manufacturers always know their product best.

In my opinion, the temperature rise it is most important factor for the difference of rated currents.

If we follow the formula (8) from Copper Development Association[UK] Copper for Busbar

which, in my opinion, is indicated for all conductor type:

I1/I2=(DT1/DT2)^0.61*[1+a20*(T2-20)]/[1+a20*(T1-20)] and if we shall take:

DT1=50oC; DT2=30;a20=0.0403 ;T2=80;T1=75 then I1/I2=1.45=993/680 [approx.]