What is the difference between knowing the thermal rating of a line and knowing the temperature of its energized conductors?
The temperature/sag/tension of an energized conductor can be measured. The line rating cannot be measured. It is calculated based on assumed or measured weather and line parameter data. Comparing the conductor temperature to the temperature limit tells the operator whether the line is operate the line but gives no guidance concerning what maximum current is allowed. The lines thermal rating tells the operator directly what the maximum allowable current is. Certain sophisticated procedures can also yield predictions of thermal ratings to warn the operator of future problems.
