Ice on power lines – and even wind alone – can be dangerous and destructive to power lines, leading to a disruption in service. Here we break down the stress ice places on power lines and infrastructure and describe a phenomenon, “galloping,” that sends power lines sailing in a dangerous way.
DESIGNING FOR BAD WEATHER
OPPD uses guidelines in the National Electrical Safety Code (NESC) and various weather condition scenarios to determine design criteria for ice load on overhead power lines. Distribution lines are designed to handle up to 1/2 inch of ice and 40-mph winds. New OPPD transmission lines are designed to handle 1 1/4 inches of ice with no wind, or winds up to 90 mph (a weak EF1 tornado) with no ice.
WIND CAN CAUSE LINES TO ‘GALLOP’
As ice accumulates on power lines, it forms a teardrop shape.
When the wind blows, wires can start to move up and down in an oscillating motion. In essence, the wires encased in ice act like an aerodynamic airplane wing. this effect is known as “galloping.”
Galloping can cause wires to eventually touch, resulting in a fault or subsequent outage. The increased movement can also cause cross-arms to break, bringing lines to the ground.
To reduce galloping and its dangers, you may see twisted wire or metal pieces attached to certain lines. This video will show you more.