Rocky Mountain Power Probes Mysterious Multi-State Blackout After 100,000 Lose Power

County 10 and Your Wyoming Link contributed to this report.

Rocky Mountain Power says it has launched an internal investigation after a massive, fast-moving outage knocked out electricity to more than 100,000 customers across Wyoming, South Dakota and Montana on Thursday — and even sparked a fire at one of its coal plants.

The company admits it still doesn’t know exactly what went wrong.

“The cause is still unknown and is currently under investigation,” Rocky Mountain Power senior communications specialist Jona Whitesides said Friday. “Given the complexity of this event, the investigation to determine the root cause and precise order of events on the system will take time.”

Rocky Mountain Power, Wyoming’s largest regulated electric utility and a subsidiary of PacifiCorp, said a large portion of its own system in the state went down as part of the wider grid disturbance. While several other utilities have said the problem started outside their systems, Rocky Mountain Power isn’t ready to say that.

“The exact duration [to determine the cause] is not known at this time,” Whitesides added.

The outage hit around 12:45 p.m. Thursday, cutting electricity to homes, businesses, coal mines in the Powder River Basin, and oil and gas refineries. Power blinked back on in some areas that afternoon, with most of the region restored later that night.

Rocky Mountain Power says the disturbance affected PacifiCorp, the Western Area Power Administration (WAPA) and Black Hills Energy, disrupting customers across three states.

WAPA, which oversees hydroelectric power and major transmission lines across the West, initially said the event was “triggered by two tripped 500-kilovolt lines near Medicine Bow, Wyoming.” In grid speak, a line “trips” when it automatically shuts off to protect equipment from a disturbance. That trip apparently led to “abnormal voltage” across the shared regional grid, causing multiple utilities and rural co-ops to shed load as safety systems kicked in.

Powder River Energy Corporation, one of the affected co-ops, said its protective systems behaved exactly as they were supposed to under those high- and low-voltage swings, even if the sudden blackout was a shock to customers.

The grid event also triggered a fire at Rocky Mountain Power’s Dave Johnston coal-fired power plant near Glenrock.

Whitesides said the fire was “quickly extinguished.” Safety systems “operated as designed,” she added, with no injuries and only some reported equipment damage.

But local officials say they were left largely in the dark about what, exactly, happened.

“I wish I could tell you exactly what happened there, and I honestly cannot,” Converse County Emergency Management Coordinator Russ Dalgarn said Friday. “They haven’t told us anything.”

Dalgarn said that kind of communication gap isn’t new, calling Rocky Mountain Power “notorious” for failing to share information with local emergency responders.

Whitesides pushed back on that characterization.

“I am surprised by that because our relationships with state and local first responders and emergency managers have been very collaborative, and we value those relationships very much,” she said.

Because of its unusual scope and impact, industry observers say the incident is more than just a blip for grid reliability.

“There’s definitely going to be accountability held at one of those federal levels,” said Joe Roth, vice president of member service at Powder River Energy.

Possible players include:

• Western Electricity Coordinating Council (WECC);
• Federal Energy Regulatory Commission (FERC);
• North American Electric Reliability Corporation (NERC), which sets and enforces reliability standards.

The Wyoming Public Service Commission also has reliability requirements for utilities. Chief Counsel John Burbridge said it appears a federal investigation may be coming, though nothing has been formally announced.

For now, Rocky Mountain Power says no outside probes have been officially launched that it’s aware of.

“While state and federal agencies may choose to conduct their own reviews, at this time we have not been notified of any [outside] investigations,” Whitesides said.

She added that PacifiCorp has already filed reports about the event with:

• The US Department of Energy;
• The Wyoming Public Service Commission;
• NERC.

The company says it’s handling the main investigation in-house, reconstructing the exact sequence of events across a complicated, multi-utility grid.

A separate spokesperson, David Eskelsen, has cautioned that a “thorough, detailed investigation may take months.”

In the meantime, Wyoming residents, local officials and federal regulators are waiting on answers to a fairly simple question about a very complex system:

What, exactly, turned out the lights for so much of the northern Plains — and how do we keep it from happening again?