power-engineeringtransmission line
I have observed that some areas have some power transmission towers painted in Red and white colors. But, more often, transmission towers are unpainted. An illustration of what I mean by this,
Left: red and white tower, right 'regular' tower
If I am right, radio/cell-phone towers are usually painted red and white, but the example in this picture is clearly not a radio tower.
So, what is the significance of a transmission tower being painted in such colors?
Wikipedia says they are ground wires to protect the live wires from lightning.
The picture shows three common arrangements of wires. I added wire-to-wire capacitor symbols, note that you also have a wire-to-ground capacitance for each wire. Capacitor values decrease as the distance between the wires increases.
Picture is own work, CC BY-SA 3.0
Case 1, Three wires in one level (equal distances to ground, but different wire-to-wire distances):
The capacitance from the middle wire to the two wires on the sides is bigger than the capacitance between the two wires on the outside of the system.
Overall, you want to have an approximately equal capacitance from each wire to the two other wires. Thus, by transposition of the wires, you create, in average, an equal distance (and capacitance) between all wires with respect to each other.
Case 2, Three wires arranged as a triangle (equal wire-to-wire distances, but different distances to ground):
Over the entire length of the system, the distances and capacitance values of the three wires with respect to each other are equal, but the wire-to-ground capacitance is bigger for the wire(s) closer to ground.
By having the three wires swapped over using transposition, each wire spends an equal averaged distance to ground. Thus, the wire-to-ground capacitance values match for the three-phase system.
Case 3, Wires neither spaced equally with respect to each other nor to ground
Now, you end up with two reasons for transposition along the total run of your line.
Best Answer
In the US, the FAA requires high-visibility markings on any tower that rises at least 200 feet above the "established terrain" (and near airports, the 200 foot requirement may be reduced). The ICAO sets similar requirements, so I'd expect roughly similar requirements in most other countries as well (though it wouldn't be surprising if some details vary).
Power transmission towers are typically around 180 feet tall, so this doesn't usually arise with them--but it can when (for example) the tower is at the top of a hill or ridge that's steep enough that the ridge itself contributes to the rise above the "established terrain". Some towers are also somewhat taller than others, and with the typical height at 180 feet or so, one doesn't have to be drastically taller than others to hit the FAA requirements--the difference in height may be small enough that it's not immediately apparent.
Reference
FAA Advisory Circular 70/7460-1L