CenterPoint Energy electric crews began the restoration work as soon as additional power generation was available.

Restoring Power and Replacing Transformers

May 7, 2021
Storm Stories Part 2: A load shedding event affected 1.4 million CenterPoint Energy customers in Houston during Winter Storm Uri.

Unlike in other parts of the country, Houston did not experience a major restoration event pertaining to damaged infrastructure on the overhead system in the aftermath of Winter Storm Uri. However, parts of CenterPoint Energy’s system did incur damage as a result of the historic weather, generation shortfall emergency, mandated load-shed and cold-load restoration activities.

At the peak of the winter storm, 1.4 million of CenterPoint Energy’s 2.6 million customers were out of power in Houston and surrounding areas. Due to an insufficient supply of electricity from power generators, the Electric Reliability Council of Texas (ERCOT) directed the regulated utility to reduce load on its system.

Reducing Load

CenterPoint Energy does not generate its own power, and outages due to the lack of generation availability were out of the company’s control. About 10 a.m. on Feb. 17, the company received the first load restore order from ERCOT, which meant that power generation sources were beginning to come back online and increasing capacity. By midnight, power generation was fully available.

By the next morning, within 12 hours of sufficient generation being restored, CenterPoint Energy was able to restore service to 99.64% of impacted customers.  By Saturday, the utility was back to normal operations.

“The linemen restored service safely and quickly, and by Saturday we were able to release resources to help other electricity providers across the state,” says Julienne Sugarek, vice president of power delivery solutions for CenterPoint Energy. “I’m proud of our people and our system.”

The last time CenterPoint Energy had a load shed event was an ice storm back in 2011, but it was of much shorter duration and fewer megawatts of load were shed.

While the load shed event was ongoing, Sugarek says CenterPoint Energy was very concerned about the state of the system.

“All the load shedding measures we were implementing were key activities to mitigate against having a black start event,” she says. “We were prepared to invoke our black start if it came to that, and we had linemen manning our black start path. I’m grateful that it didn’t happen, but it was an activity that we were prepared to do.”

Replacing Transformers

After generation had been restored, CenterPoint’s linemen shifted to the task of addressing outages related to equipment failures. When CenterPoint Energy began performing “cold load pickups” by turning on the circuits that had been off for a period of time, it put a strain on the system. Sugarek compared the process to trying to pedal a bicycle. When you first start pedaling, the first few rotations take extra muscle power to overcome inertia and gain momentum. In the same vein, restoring customers requires additional power to get the equipment in motion.

“For a short period of time, the power demand is high, and then it stabilizes, which puts extra stress on your equipment and your transformers,” she says.

In turn, linemen had to replace more than 1,000 residential pad-mounted transformers, which failed as they were coming back online. The average time of each of these transformer replacements took 3.5 to 4 hours, as the vast majority of these URD transformers were in backyards or not accessible by trucks.

Prior to the winter storm, CenterPoint Energy ramped up its transformer inventory. When necessary, the linemen had to repurpose transformers from buildings that were not yet operational for existing customers.

“Our supply chain made sure we had the inventory on hand that we needed for what we faced,” Sugarek says. “We were even able to offer our inventory to other impacted utilities. It’s part of our mutual assistance effort to not only supply people with skills to make repairs, but also inventory.”

Focusing on Resiliency

Houston didn’t experience significant snow and ice accumulation, but CenterPoint Energy experienced some minor and isolated damage to its infrastructure due to icing.

“When the wind is hitting the lines at a particular speed and a particular direction, it creates a situation where the wires are moving up and down or oscillating,” Sugarek says. “We saw some instances of this occurring, but we have been doing a lot of work to proactively mitigate the galloping condition.”

For example, CenterPoint Energy retrofits its transmission lines to prevent galloping conductor conditions.  Linemen have installed anti-galloping devices on the conductors to suppress their movement under ice and wind conditions to avoid outages. These devices attach at the point where the power line is at its lowest—in the middle of the span—to prevent the oscillating motion from occurring. As a result, CenterPoint Energy was able to minimize the ice-related outages, and its transmission and distribution system withstood the extreme weather and demands of the load shed event.

“The investments that we have made in our grid resiliency have been very effective,” Sugarek says.

Learning from the Event

With the temperatures dipping near single digits, the storm brought about challenges for CenterPoint Energy’s customers in Houston and surrounding areas.

“What made this event unique was the duration coupled with the generation shortfall,” Sugarek says. “It was very cold over a fairly significant period of time, which had a huge ramification for a lot of people in our service territory.”

To help the families who were impacted, the mayor of Houston set up a Houston Recovery Fund. CenterPoint Energy has donated $1 million and is working with other corporate partners to secure additional contributions, and its CEO is chairing the effort.

Looking ahead, CenterPoint Energy, like other T&D companies and along with other stakeholders in the electric market, will look for ways to improve their response to load-shed events in the future.

“I think anytime you have a major event like this, you have to use it as an opportunity to learn,” she says.

Sugarek says CenterPoint Energy wants to be part of the solution. The company said it is fully committed to working with the Governor, Texas Legislature, Public Utility Commission of Texas, the ERCOT, Texas power generators, and all stakeholders to take measures to address the issues related to this historic winter storm.

“We appreciated our customers’ continued patience during this very difficult event. In my case, I hope it is a once-in-my-career situation, and I hope that others that come after me will never experience it,” Sugarek says. “Our ability to restore approximately 1.3 million customers in a 24-hour period was not only a testament to our employees’ dedication and perseverance, but it also reinforced the value of the investments we have made in our systems and infrastructure.”

Amy Fischbach ([email protected]) is the Field Editor of the Transmission and Distribution World magazine.

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