By Justin Lee
Rolling blackout is not a new term in the utility world. Countries in Europe have been subjected to it routinely over the past several months. We’ve seen it happen during recent summer heatwaves in California and the Texas transmission grid failure in winter 2021. But Cullman Electric Cooperative had never in its 86-year history experienced a rolling blackout prior to Christmas weekend 2022.
On the morning of Dec. 23, 2022, an arctic cold front moved across the southern U.S., and temperatures plummeted to record lows. Our power provider, the Tennessee Valley Authority, was nearing record-high system load, with all generation units running as well as purchased power being fed into the TVA grid from outside the valley. Early in the morning, two of the main generating units at TVA’s Cumberland Fossil Plant in northwest Tennessee went offline. The loss of this plant as well as two other small gas generation units, forced TVA to implement its Emergency Load Curtailment Plan (ELCP). As the sun started to rise, temperatures outside did not, and the extreme demand for electricity resulted in TVA escalating from ELCP Step 10 and Step 20 at 8:30 a.m. all the way to Step 50 by 9:30 a.m.
When an ELCP is activated, Step 10 and Step 20 are simple. Step 10 is in-house load reduction. That’s when the co-op turns off the lights in the hallways and cuts back the thermostats a few degrees. Step 20 is a public appeal for voluntary load reduction. The communications team will contact our local media and post energy-savings tips on social media. ELCP Step 10 and Step 20 are rarely activated but happen on occasion during the hottest summer days or on very cold winter mornings.
Step 50 — when rolling blackouts begin — had never before been issued by TVA. At Cullman EC on the morning of Dec. 23, the Step 50 notification called for a five percent reduction to get through the morning peak. We were able to cover this reduction thanks to the quick response of several large industrial customers, including Cullman Castings, Rehau, Topre, Tyson, and Louisiana Pacific. These quick actions are the sole reason Cullman EC residential members did not see rolling outages that morning, while some of our neighboring co-ops in North Alabama were not so lucky.
TVA staff worked around the clock to restore Cumberland in hopes that Step 50 could be avoided the next day; however, during the night, their purchased power from outside of the valley was curtailed due to similar issues in other parts of the country.
Cullman EC was notified around 4 a.m. on Christmas Eve that another ELCP Step 50 was imminent. Engineering and operations staff reported to the office, and by 5:30 a.m., the call came through, this time requiring a 10 percent reduction of system load. Using our internal Step 50 protocols — which are reviewed and updated every year — we immediately initiated our in-house schedule for rolling blackouts.
This was a situation no one ever wants to face, but the good news is our emergency response plan worked. By the end of the rolling blackout at 11 a.m., Cullman EC had rolled 40 station breakers in just over five hours, affecting over 33,000 member accounts. Most members experienced a power outage that lasted no longer than 20 to 25 minutes. In the process, Cullman Electric did its part to prevent any long-term blackouts across the TVA system.
At Cullman EC, we have already identified several ways to make our emergency response plan better both operationally and systematically. We will continue to plan, upgrade, maintain, and improve our system, so we are prepared for the days we hope will never come.
Justin Lee is the Manager of Engineering & Technicians at Cullman Electric Cooperative.