Galloping power lines
Transmission lines are designed to withstand galloping. However, if the energized conductor gets close enough to any grounded part such as the steel of the tower, the grounded skywire, or another energized conductor, a short circuit fault occurs momentarily until protection devices (such as relays and circuit breakers) interrupt the flow of the short circuit current. This is what causes lights to flicker intermittently.
If you see galloping transmission lines, stay clear. Do not approach the transmission lines or towers. Potential dangers include ice dislodging and flying off the lines or power lines breaking loose.
Galloping can occur when freezing rain collects on transmission towers and conductors, trees, and any other objects. Then icicles and odd-shaped ice can form on the conductors; that’s called ice accretion.
When wind pushes on those icicles and conductors, this causes uplift on the iced-up conductor and a consequent galloping, or jumping, motion occurs. Power lines can sway in high winds, but it’s the combination of wind and ice that causes them to gallop more forcefully.
Six millimetres of ice and a steady wind of at least 30 km per hour perpendicular to the transmission line are ideal conditions to create galloping.