Can the wind blow the power?
SIOUX FALLS, SD (KELO) – Power poles and power lines are out there facing steady winds of over 30 mph and gusts of over 60 mph like South Dakota and other parts of the region of the five states have had this week.
According to Billy Gibson of the South Dakota Rural Electric Association (SDREA). SDREA has 28 power cooperative members in South Dakota.
“In terms of the impact of strong winds, what we are generally concerned about is a phenomenon called ‘galloping’ which occurs when the force of the wind causes the driver to move or sway rhythmically and ultimately create a vibrating effect or gallop,” Gibson said. .
“(The galloping) can cause the conductor to stretch and sag below prescribed ground-line tolerances and damage poles, insulators and other structures,” Gibson said.
The Northwest Iowa Power Cooperative (NIPCO) based in LeMars, Iowa, provides power and transmission to members in western Iowa.
NIPCO’s website describes galloping as “when ice storms blanket power lines, high winds can cause lines to bounce and rear up.” Moving lines can be pushed against a grounded component or live conductor and a short circuit will occur.
The power lines that NIPCO uses to transmit power over its 69 KV (kilovolt) high voltage power lines in western Iowa are designed to withstand up to 1.5 inches of ice and high winds. 50 mph, according to its website.
Galloping is always a possibility, especially if there is ice and high winds, said NIPCO’s Angela Catton. Catton, who said she was speaking as someone who works with energy education partners and not as an engineer, said that while the lines are strong enough to withstand high winds, there may still be flickers in the current or short outages due to galloping.
As of 1 p.m. April 7, “After three days of severe wind advisories, there have been no significant outages on our cooperative systems caused by wind,” Gibson said of SDREA.
West River Electric Association Inc. owns about 40,000 utility poles in the Black Hills area which includes Sturgis 20 miles east of Wall and up to Scenic, said Mike Letcher, operations manager.
West River’s distribution system covers nearly 100% in an area of 4,500 square miles, according to its website.
Utility pole designs and the way lines are strung have changed over the past 40 years, Letcher said.
“We use taller poles with shorter spans,” Letcher said. “We have reduced the distance between the posts. The wind range is halfway between one pole, through the next pole and halfway between the (third and second pole).
“Wind reach generally applies to high voltage transmission power lines that are seen in large open rights-of-way that are constructed and designed to carry electricity from a generating facility over long distances of land via a transformer step-up or step-down process and in a utility substation system,” Gibson said.
According to industry websites, the the wind range is defined as half the sum of the adjacent spans or being determined by the wind load on half of the span leading to a pylon plus the wind load on the half of the span away from a pylon.
The wind range is used to calculate the force applied to the structure due to a horizontal wind blowing on the conductors.
The shorter the distance between poles, the less vulnerable power lines are to wind, Letcher said.
Trampolines can sometimes be a bigger problem than the wind, Letcher said.
“We had trampolines stuck in the power line. It’s a lot more common than you might think,” Letcher said. People don’t often think about anchoring their trampoline in strong winds.
“The wind blows this trampoline…” Letcher said. “We had several (trampoline incidents) but none in the last week.”
SDREA co-ops build to meet all National Electrical Safety Code (NESC) requirements and rural utility standards, Gibson said.
“Codes vary by region/climate and are designed to ensure the system can withstand ice, wind and other adverse conditions that may exist in certain parts of the country,” Gibson said.
Letcher said a standard utility pole is 40 feet tall. Diameter size may change.
Pole diameters range from 5 to 00. The smaller the number, the larger the diameter.
“We used to use class 5, now we use class 4 for our two-phase system and class 3 for our three-phase system,” Letcher said.
A three-phase system would have three hot wires and one neutral wire, he said.
Above ground or underground?
Gibson said that while installing power lines below ground can protect the lines from ice and wind, there can still be problems.
It often takes longer to diagnose problems with an underground line than with an above-ground line, Gibson said.
Because sophisticated equipment is required, it’s more expensive to find the problem and fix it, Gibson said.
It’s also more expensive to install power lines underground than to install lines above ground, Gibson said.
“Finally, overhead lines have a useful life that is twice the useful life of underground lines, typically around 50 to 75 years versus around 30 years for underground lines,” Gibson said.