RAPID CITY, S.D. – A regional transmission event in Wyoming was the root cause of the widespread power outage that impacted thousands of customers in the Rapid City area and throughout parts of South Dakota, Wyoming, and Montana on Thursday, utility officials confirmed.
Wes Ashton, Vice President of South Dakota & Wyoming Utilities said “The last time I can recall an event that had a systemwide impact was winter storm Atlas”.
WyoFile reported the incident, which occurred just before 1 p.m. MST, was triggered by two tripped 500-kilovolt transmission lines near Medicine Bow, Wyoming, according to Stephen J. Collier, a public affairs specialist for the Western Area Power Administration. This initial event caused an abnormal voltage spike across the grid that subsequently tripped numerous surrounding transmission lines, knocking generation facilities and substations offline across multiple states.
The cascading failure affected several electrical utility providers, including Black Hills Energy. The regional power loss prompted Black Hills Energy, which serves customers in South Dakota and Wyoming, to initiate its emergency response plan to safely re-energize its system.
Black Hills Energy stressed that the source of the outage was a facility located outside of their operational territory, according to information posted on their website. The scale of the event was highly unusual, affecting interconnected utility providers across the region.
Outage Timeline Summary
The power restoration process was complex, requiring a phased approach to ensure system safety and stability, pushing restoration efforts into the evening hours.
- 12:45 p.m. MST: The widespread outage began after two 500-kilovolt lines tripped near Medicine Bow, Wyoming (WyoFile).
- 1:40 p.m. MST: Black Hills Energy personnel activated their response plan to address the regional electrical outage impacting the South Dakota and Wyoming service areas.
- 2:30 p.m. MST (approx.): Approximately half of Black Hills Energy’s impacted customers had power restored as the system began to be re-energized in segments.
- 4:30 p.m. MST: Restoration efforts continued across the affected region, with utilities warning that power delivery could remain unstable for a period.
- 8:30 p.m. MST: Black Hills Energy reported that power had been restored to nearly all customers affected by the regional transmission incident (Black Hills Energy).
