What are power lines made out of?
Mostly aluminum because they are ran in free air and that changes their ampacity rating enough for aluminum to be more economical than copper. Gold has a higher ampacity rating than either al. or copper but it is to valuable to leave hanging in the air.
Power lines sag mostly in the summer depending on where you live. The warm weather causes the power lines to expand ( so the particles expand) and sag. If you live in a Northern Country where it is cold in the winter, the power lines will do the opposite because the cold weather causes the power lines to contract. So basically power lines sag in the summer and "de-sag' in the winter.
Power lines and phone lines though using the same utility poles are two different sets of wires. Telephone wires carry their own power, separate from the power lines and are insulted while power lines are not. If the telephone wires are unbroken but laying on the ground the wires will not short to ground while an unbroken uninsulated power line will short to ground disrupting service.
Sagging Power Lines In the summer, power lines warm up with the weather. Since materials expand when they get warm, the power lines stretch out and sag. The opposite happens in the winter, as the power lines get colder, they contract. Also, in the summer the electrical load on the line is generally greater. This in turn causes increased temperature and can lead to the line sagging.
A generator contains magnets which can be rotated; as their magnetic lines of force pass through surrounding wires, they generate electricity. In order to create the necessary rotation, various mechanisms are used, such as steam turbines (steam can be made using either fossil fuels or nuclear power), wind, or flowing water. Photoelectric power is made in an entirely different way, but that is not used at power stations.