NOTE: Information on this incident is developing and is subject to change pending new information.

SUNDANCE, Wyo. - On Thursday, November 13, Powder River Energy Corporation (PRECorp), a rural electric distribution cooperative serving northeast Wyoming, experienced an unprecedented power blackout and voltage instability beginning approximately 12:45 p.m.

The resulting outage cut power to every PRECorp service, more than 27,000 meters in Campbell, Crook, Johnson, Sheridan and Weston counties in Wyoming and parts of southern Montana.

Local media have reported the blackout resulted from power problems at a 500 kV transmission line near Medicine Bow. Cascading events rolled toward the PRECorp system and also affected electric providers at Montana-Dakota Utilities, Rocky Mountain Power, Black Hills Energy, Basin Electric, and Gillette City services. At its peak, more than 100,000 services from Casper to Rapid City to Sheridan and the northern edge of Cheyenne were impacted.

In response, PRECorp deployed line crews to nearly all of its 30-plus substations to prepare to safely restore power to circuits across the system. “We wanted to have eyes on every substation before it was energized,” VP of Engineering Quentin Rogers said. “We avoided some problems for sure.”

The restoration process began approximately 3 p.m. as incoming voltage stabilized and PRECorp crews prepared equipment settings to be re-energized. Crews successfully restored power to communities through individual substations beginning approximately 4:30 p.m. and final services were restored approximately 9 p.m.

PRECorp officials said the response was aided by favorable weather conditions that allowed linemen and others to access all facilities. Although the sudden loss of electricity across an entire region came as a jolt to residents and businesses who operate here, the PRECorp systems that protect infrastructure and consumers performed as designed as it responded to the high and low voltage scenarios. At this time, no employees were injured during the response and restoration. The PRECorp team operated nearly every switch and breaker on November 13, with only a few problems detected.

PRECorp is assisting with the investigation into the impact of this widespread and unprecedented incident.

Other notes:

• PRECorp line crews, distribution design technicians, engineers, and information technology teams will conduct routine evaluations of equipment in the coming days and weeks to identify any damage that might have occurred during this incident.
• Members may experience additional power issues from damaged arrestors, particularly during wet weather. Call the 24-hour PRECorp outage number 1-888-391-6220.
• Scammers are likely to take advantage of this event to unlawfully solicit members’ personal information. The only number you can trust when dealing with PRECorp is 1-800-442-3630.
• PRECorp CEO Brian Mills will host a telephone town hall meeting for members at 6:30 p.m. Thursday, November 20, to answer questions about the incident. The meeting will also be carried live on Facebook.