Nearly 4,000 residents and business customers went without electricity and heat for between seven and 10 hours as overnight lows dipped to the teens.
The loss of power also affected multiple companies in the oil patch.
A malfunction with a Mountrail-Williams Electric equipment started the chain reaction affecting both their customers and users of Montana-Dakota Utilities (MDU).
"A transformer blew up over by Tioga, and the fault that it put on our line caused an underground cable to go bad east of Ray," said Mountrail-Williams Electric Cooperative spokesman Mark Holter. "That fault went back to our Ray substation, and fed through to MDU's transmission line, and opened up a breaker on their transmission line. That's what took out Ray, Tioga, and four of our substations. Right now, we've got everybody back on." Holter said the power source was diverted to resume service. Meanwhile, repairs to the damaged areas were expected to be completed by early last evening.
Some 3,000 city customers in Wheelock, Ray, Tioga, Epping and Spring Brook and 800 rural residents/commercial customers began experiencing power outages at about 3:30 a.m. Thursday, according to Holter.
Steve Rock, electric operations manager for MDU's Williston Office, said power was restored for their customers by 9:35 a.m. Thursday. He added crews patrolled lines until noon to assure there was no problem within the MDU equipment.
"We had four sub-stations. It's the Ray substation, the Tioga substation, Pleasant Valley which is south of Tioga and Hoffland Substation which is south of Ray. ...It was probably 700 to 800 of our customers. A lot of it was commercial, and a lot of oil companies out," Holter said.
"It was an unusual outage for us," Holter added. "We have equipment that when there's a fault on the line - this time it was a transformer on a pole over by Tioga that went bad. Typically, when a fault like that happens, it opens up a device that shuts the power off on that line.
"This time, it actually fed through a device and went all the way to MDU's transmission line which (messed) their transmission line up. We had to be cautious of bringing on different loads so we wouldn't trip it again. It took a while. When you have something that is difficult to find, and it's at the end of the line, you keep sectionalizing that. You keep dividing up the system, trying this, trying that until you finally narrow it down to the problem."
He explained the problem was located just a little bit east of Ray. "It was an underground cable - a 7,200-volt line. More than likely the fault in the line was caused by the transformer that blew up over by Tioga."
Power sources were diverted to allow for repairs.
He said everything but the Ray substation had power returned by 11 a.m. Thursday.
"We narrowed it down to the substation that goes to Tioga," he said. "We didn't get some people back on until 1 p.m. this afternoon. It was about a 10-hour outage for some areas."
Holter said the cooperative knows the urgency of getting power restored in these instances.
"We want to get this power on as fast as we can," he said. "People have businesses. They got things going on at home, little babies, people at home not feeling well. We don't like to see an outage go very long at all."
Holter said the Tioga Medical Center had a back-up generator
He added that oil-related companies experienced their own shutdowns as a result of the power lapse. "They'd call in periodically and want updates. We know how important it is for them to get things up and running too," he said.
"We got everybody back on at 1 p.m. We have crews that will locate that bad spot. We have special equipment that is able to tell us what the bad spot is. We dig it up, find it and repair it," he said.
Holter said he expected that repairs were to be completed by early last evening.
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