LEW HANES: Are transmission lines affected by time of year?

BILL MELTON: Transmission lines are sagged according to the maximum amount of load that can be transmitted over these lines, according to the material make-up of the conductor itself, at a maximum ambient air temperature at the line.  Some of them will be designed with 95 degrees as the design air temperature.  That means that at 95 degrees air temperature, the line will carry an acceptable load and will sag within required specifications.  If the temperature is 40 degrees, you increase the capability of that line significantly.  It's called dynamic line rating.
Additionally line maintenance is normally performed during the spring and falLew Hanes: This is primarily due to light load and mild weather conditions

LEW HANES: You said sag?

BILL MELTON: Yes, it is the droop that you see on a transmission line.  The line, for example, might be designed with a sag for 95 degrees air temperature, and is rated at 1,000 amps.  If at 95 degrees you surpass 1000 amps, that line will actually sag or droop beyond required clearances.  If it's 40 degrees outside, you've actually increased the capability of that line from 1000 amps by as much as possibly 200, 300, or 400 amps.

In the winter we have very few problems with our transmission system capacity.  As the temperature goes down, the dynamic line ratings go up.  In the summer it's quite the opposite, as the temperature goes up, the line ratings go down.