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Crews restore power after blizzard, tornadoes damage UGP transmission system
by Chris Lyles

 UGP crew members repair H-structures that were destroyed during tonadoes in early October

An Upper Great Plains line crew removes a damaged H-structure from the Sioux City-to-Denison 230-kilovolt line outside of Sioux City, Iowa, early in October. The structure, along with six others, was destroyed when tornadoes swept through the area days earlier. (Photo by Tim Ruge)
Operations and maintenance personnel from Western's Upper Great Plains region had their hands full on Oct. 4 when blizzards in South Dakota and tornadoes in Iowa pushed the electrical system to the point of failure. The heavy snowfall and high winds in one portion of the region and tornadoes in another beckoned several UGP maintenance crews to brave treacherous working conditions and restore customers’ power in record time.

Unlike any storms UGP had seen before, both events had catastrophic effects on the region’s transmission system. UGP Maintenance Supervisor David Hinders said, “The lines started tripping on the afternoon of Oct. 4 and we knew we could possibly experience a subsequent line failure.”

Snowdrifts slow crews response in SD
Snow and ice was accumulating on the transmission line conductor and the windy conditions had the conductors bouncing and whipping uncontrollably. Wooden crossarms and metal hardware could no longer take the strain and eventually dropped the conductor to the snow-covered ground, causing the circuit to trip offline and cutting the flow of electricity to several of Western’s customers.

On Oct. 4, some areas of South Dakota reported up to 48 inches of accumulation. According to the National Weather Service, this area typically experiences an average annual snowfall amount of 42 inches per year, proving this storm was uncharacteristic.

The snowdrifts and blizzard conditions hampered crews’ quick response in South Dakota. “Western maintenance crews from several offices mobilized as soon as possible to assess the damage and begin formulating a restoration strategy,” said Hinders. “It took almost four hours for one member of the [South Dakota] crew to travel ten miles from his house to Western’s shop due to the poor road conditions,” said Transmission Line Maintenance Engineer Lila Vaselaar.

The heavy, wet snowfall and 70-MPH winds took their toll on two circuits west of Pierre, S.D. A 115-kilovolt circuit between Wall and Wicksville substations lost 11 wooden H-frame structures while a northern 230-kV route from New Underwood Substation to Maurine Substation lost 15 of the same type structure. Western’s helicopter pilot and line crews assessed the initial damage in South Dakota since quick access was limited by the deep snow.

Equipment overcomes terrain
Although travelers might expect to see flat grass prairies across South Dakota, the structures most devastated by the storm were not in easy-to-access portions of the landscape. “The crews experienced rugged terrain, slippery clay soil and steep slopes in the vicinity of both northwest Iowa and along the Cheyenne River valley in western South Dakota,” said Vaselaar. Crews used crawler-type man lifts and cranes, which are equipped with metal-cleated tracks rather than traditional rubber tires and therefore more effective in mud and snow, to access the damaged transmission structures.

UGP Transmission Operations Manager Michael Kirwan explained, “The primary concern was restoring the integrity of the bulk electrical system and getting service back to our customers that we had dropped due to Western’s transmission line and substation damage.” Some customers lost power for about 26 hours while crews worked to repair the heavily damaged 230-kV and 115-kV electrical system, including transmission lines and substation equipment.

Crews quickly counter Iowa tornado damage
Damage assessment in Iowa was ascertained by ground crews and repairs to the tornado-ravaged area began quickly. Multiple tornadoes—one of them a mile wide—struck Iowa, Nebraska and South Dakota, injuring up to 15 people and causing significant damage, according to meteorologists and local authorities. During the event, seven H-frame structures on the Sioux City-to-Denison 230-kv circuit also fell prey to a series of tornadoes that swept through the area just southeast of Sioux City.

Ready supplies support quick repairs
“The majority of the materials needed for the repairs were already on-hand in Western’s inventory,” explained Vaselaar. Crews work their way down the de-energized line, first “wrecking” the broken and mangled structures from the right of way, then replacing the structures and reconnecting conductor. Many of the new crossarms come preassembled with the required hardware, which helps methodical and orderly assembly. “Our maintenance crews did a fabulous job of getting the system back up and running in record time under extreme working conditions—we are very proud of them,” said Vaselaar.

Western crews had the bulk of the 115-kV system repaired, operationally functional, and power available to all of Western’s affected customers within 26 hours of the lines being removed from service, and all other permanent repairs made in South Dakota and Iowa within three weeks. “UGP outage coordinators and dispatchers were diligent during this event. It’s a comforting feeling to have experienced and capable people on the desk when system elements start to fail,” said Kirwan. “Stuart Dahlin, a veteran dispatcher, was on the south area dispatch desk when the lines originally started tripping—you couldn’t have hand-picked a more capable person.”