It could take months to pinpoint what caused two high-voltage transmission lines to trip near Medicine Bow last week, resulting in an unprecedented blackout that impacted about 100,000 customers of multiple utility companies across Wyoming, Montana and South Dakota.
The investigation will focus on the sequence of events leading up to the Thursday afternoon outage that began around 4:45 p.m., according to David Eskelsen, a spokesperson for Utah-based Rocky Mountain Power, which had the most customers without power.
“The reason this takes time is that we must examine the data recorded by our system monitoring,” Eskelsen, who declined to speculate on the cause of the blackout, said in an email Tuesday. “We want to be thorough before we draw any conclusions.”
The outage temporarily removed 3.8 gigawatts of power across wind and thermal generation facilities, impacting PacifiCorp (which owns Rocky Mountain Power), the Western Area Power Administration, and Black Hills Energy.
Domino Effect
The blackout sparked a small fire at the PacificCorp-owned Dave Johnston Power Plant in Glenrock. The plant’s fire suppression system quickly extinguished the blaze, and no injuries were reported.
However, some equipment was damaged, Eskelsen said.
The two 500-kilovolt transmission lines that tripped are located in southern Wyoming and caused an abnormal voltage event that cascaded along Western Area Power Administration lines, resulting in further outages across the region, WAPA reports.
The power surge caused at least seven fires in Sheridan County, ranging from half an acre to 50 acres. Ranchers and volunteer firefighters quickly put out the fires.
Hospitals throughout the region used emergency generators to cope with the outage.
What Now?
Although state and federal agencies may choose to conduct their own investigations into the blackout, Eskelsen said he is not aware of any independent probes.
PacifiCorp, which operates the largest electric grid in the Western U.S., has submitted reports about the outage to the U.S. Department of Energy, the Wyoming Public Service Commission, and the North American Electric Reliability Corporation (NERC).
John Burbridge, chief counsel for the Wyoming Public Service Commission, declined Tuesday to comment on the outage. The Department of Energy and NERC could not be immediately reached for comment.
On Barrasso’s Radar
U.S. Sen. John Barrasso, R-Wyoming, is also monitoring developments surrounding the outage.
During Monday’s Casper Rotary Club meeting, Barrasso received a personal update about the outage from Rocky Mountain Power Regional Business Manager Mike Morrissey.
“He will continue to request updates as Rocky Mountain Power investigates the cause of the blackout,” said Laura M. Mengelkamp, Barrasso’s communication director.
She did not disclose what was discussed at the Rotary meeting.
Powder River Energy Corp. in Gillette, which was affected by the outage and partners with Black Hills Energy, also wants information about the cause of the blackout to ensure another similar outage doesn't happen.
“We also recognize the importance of utilities providing accurate, verified details through a thorough analysis, and more specifics are expected once that process is complete,” said Tim Velder, a spokesman for the utility.
Converse County Emergency Management Coordinator Russ Dalgarn said he and colleagues across Wyoming have contacted Rocky Mountain Power officials but have not been provided details regarding the possible cause of the outage.
“It’s not a very good working relationship to have,” he said, adding that other emergency management coordinators are equally frustrated.
Scott Schwebke can be reached at scott@cowboystatedaily.com.
