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Almost Half Of San Antonio Lost Power During Winter Storm; CPS Circuit Map Shows Affected Areas

CPS Energy
A low-resolution map of circuits that were shut off during the energy crisis. All circuits depicted here — red and blue — were affected during the storm and lost power at some point. Red circuits here have higher voltage than blue. TPR has requested a higher resolution version of this map but was initially told one could not be released due to security reasons.

Nearly 50% of the San Antonio area lost power during the winter storm and energy crisis last month. About one-third of CPS Energy’s circuits were taken offline.

A map released by CPS details which circuits the utility had to take down in order to keep from overwhelming the state’s power grid. It’s a complex pathway displaying which portions of the city had to go without power from the start of the rolling outages to several days in darkness with brief bursts of electricity.

On the morning of Feb. 15 — as snow was piling up across San Antonio — tens of thousands of people lost power in rolling blackouts.

CPS Energy calls this a load shed; the utility had to cut power in mass because of the Electric Reliability Council of Texas' demands to reduce power.

“In this event the whole goal is keeping the grid up — so this (was an) emergency, last-ditch operation to keep us up,” said Paul Barham, CPS Energy’s Chief Grid Optimization and Resiliency Officer.

About 400,000 homes and businesses lost power throughout the crisis.

“I think that would have included outages for all reasons, so load shed as well as outages due to failures,” Barham said.

The utility has about 866,000 customers in Bexar County and some surrounding areas. CPS is still trying to determine how long some went without power.

The 2021 winter storm was unprecedented for Texas in strength. It took dozens of power plants across the state offline due to extreme cold which is what triggered ERCOT to issue the calls for rolling outages. Those outages left millions of Texans without power.

However, it’s not the first time it’s happened. In 2011, similar rolling outages were issued during an intense cold weather event that also took power generation offline but the outages lasted less than a day.

This extended power crisis led to the question of who was losing power and why. There were accusations that the utility had cut power to low-income areas which Barham said is not true.

“I can tell you that lower income areas were absolutely not targeted,” he said.

Where those outages were happening wasn’t decided by a person as the crisis unfolded. It was a computer program.

“We came into this event with a program that would automatically manage load shed and as I mentioned during the presentation to the (CPS Energy Board of Trustees) that was actually an improvement we had made from the 2011 event so we were coming comfortable that that was going to provide really a better experience,” said Barham.

It didn’t work exactly as planned, though.

“But that amount of load shed that became required was beyond what the program could handle,” he said.

For CPS Energy, the outages for homes and businesses were spread out over circuits. Which circuits would lose power were predetermined, however.

“The automated system was working from a set of circuits that was predefined so there was decision making around that,” Barham said.

A circuit map displayed at that CPS Energy Board meeting this month shows the outages were spread all over Bexar County.

“All the circuits that were utilized for load shed at any point during the event were shown on that map,” Barham said.

CPS Energy Map - Circuits.png
CPS Energy
A slide showing the load shed circuit map was provided to CPS Energy Trustees at its Mar. 1 meeting.

The map is a spider web of circuits. Outside of Loop 410 on the North Side, there are long tangles of circuits that went dark, while inside the loop it shows entire areas without power. Other darkened circuits reach out into Comal, Atascosa and Medina counties.

Texas Public Radio requested a higher resolution image of the circuit map but a CPS Energy spokesperson said they couldn’t release it due to security reasons. Barham and the spokesperson said they were trying to create another map that could be released publicly.

The map displayed during the board meeting shows red and blue circuits, but Barham said that has nothing to do with who lost power. The red circuits are higher voltage.

CPS Energy has about 600 circuits. And it’s divided into three groups based on how critical those circuits are. The first group is tied to frequency management — an essential process to maintain system stability.

“Then a second (group) is associated with these critical loads such as our military bases,” Barham said.

That also includes hospitals, fire stations and police stations. Following that is everything else where the overwhelming majority of power outages occurred.

“And then, really, the circuits left for the load shed activity is what’s left over after that. The challenge is how do we increase that number of circuits that are available for load shed so the outages are not as long as they were,” Barham said.

It’s this third tier of circuits that were issued rolling blackouts in the beginning of the winter storm, which then lead to hundreds of thousands being without power for extended periods of time. Barham said the system is being examined now.

“The challenge is how do we increase that number of circuits that are available for load shed so that the outages are not as long as they were,” he added.

There was a mistake where some of those circuits that contained San Antonio Water System pumps were taken down which left many people without water. As much as 30% of the city lost water through lack of water pressure and weather related pipe bursts in homes.

“The SAWS pump — when that was identified to us — we then put that into a circuital circuit status where we wouldn’t be rotating outages on that.”

Each circuit in the system has about 1,500 to 3,000 homes and businesses attached to it — and that’s a rough estimate because every circuit is different. The red circuits indicated in the map have more customers on them.

Rolling outages were meant to only last 10-15 minutes at a time, but the energy reduction requirements became too high to restore power as the crisis evolved. Instead, people experienced long periods of no power and short bursts of electricity. CPS Energy released a list of answers to questions on Feb. 19, partially explaining this:

“To meet our required share of the load shed demand reduction, the duration of time circuits were off-line had to increase to a point where customers experienced extended outage periods and only brief periods of power. We adjusted our processes throughout this event to respond to the unprecedented levels of required load shed. We wanted to provide relief to customers who had been without power, but equipment limitations and failures occurred, resulting in the extended outage periods experienced by many.”

With the current urgency of figuring out how to pay ERCOT and natural gas providers for the energy it had to buy, CPS Energy is examining how to prevent a crisis like this from taking place again.

Barham said one of the first steps taking place in a potential revamp of the load shed system is working with the provider of the automated system which issued the first blackouts.

“I think ultimately to get really significant improvements, there’s going to have to be probably applications from different technologies that allows to better break up the system and take smaller pieces of the system out and not complete circuits, that’s something that’s probably much further down the road,” he said.

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