Texas, CPS Energy, transmission towers, storm restoration
Crews position equipment to remove conductor from the other side of the damaged 345-kV tower.

Texas Twisters Total Transmission Towers

Linemen repair infrastructure and restore power after four tornadoes snapped distribution poles in half and mangled transmission structures.

A severe storm slowed down west of San Antonio, Texas, before suddenly picking up strength and speed. It then rammed into CPS Energy’s service territory like a locomotive, disrupting power and destroying infrastructure.

Several different storm lines intersected outside the city, sparking four separate tornadoes that obliterated homes, wood poles and transmission towers. Winds of more than 100 mph knocked down trees and inflicted damage in the heavily developed north and northeast side of San Antonio.

While the city has experienced severe weather in the past, the tornadoes had rarely touched the core of the city. As such, it became one of the most destructive storms the city — and CPS Energy — had seen in at least three decades. Tornadoes tore across four different transmission corridors, but only caused failures and significant damage in one corridor. The utility was thankful that the devastation wasn’t even more widespread.

One crane supports part of the damaged 345-kV tower while another crane sets up to move the conductors off of the tower.

Twisted Towers

When the tornado touched down in northeast San Antonio, four transmission towers were in its path. Two towers, which were located 850 ft apart and served two different circuits, failed completely. Meanwhile, two other towers were damaged and will need to be replaced eventually.

Of the two towers that failed, one tower buckled at mid-height and crashed down to the ground, knocking out distribution lines and power to local residents and businesses. This tower was built directly behind an elementary school, and one of the circuits crossed over the school and the homes located near the right-of-way.

After the tornado took down the towers, the system operator alerted CPS Energy’s transmission lineman group that a line went down and both circuits were affected. That night, the linemen arrived on site to assess the damage. In addition, they called two line contractors away from other projects to provide assistance. The next morning, the contracting crews were on site and moving cranes, bulldozers, pole diggers and pickup trucks into position in the muddy right-of-way.

CPS Energy then assigned one contractor crew to work on one tower and the other to focus on the second tower. The utility’s foreman and manager oversaw the two contracting crews to ensure that work was getting done safely and efficiently.

At the peak of restoration, when more than 84,000 of CPS Energy’s customers had no electricity, about 70 linemen were on site to restore the transmission lines, including about 12 from the utility. With warmer weather on the way, the crews tried to work as swiftly as possible to ensure the circuits were restored to support higher loads for the customers.

With part of the damaged 345-kV tower supported by a crane, crews survey the damage before beginning work.

Restoring Power

Following the tornadic activity, the contracting crews from North Houston Pole Line and Maslonka Power Line Services manually cut up the disfigured towers, untangled them from the conductor, and then used a crane to remove the tower piece by piece.

To restore power, the linemen erected temporary wood structures so one of the circuits could become re-energized. The distribution crews punched holes for three sets of wood structures. The linemen hung one of the 345-kV circuits in a vertical configuration with one pole per phase.

Fortunately, CPS Energy’s transmission department was prepared for emergency situations. A few years ago, the senior director asked his group, “What does a bad day look like in the transmission world? What do we need to do to be prepared for tower failure?”

The linemen responded that a total tower failure would be the most severe result, so the department ensured that long poles are on hand in its yard to prepare for such a severe weather event. In addition, CPS Energy stocked the hardware so it could quickly respond following a storm or other emergency.

Using these on-hand materials, the contracting crews quickly performed the work necessary to energize one of the two downed circuits. Through hard work and cooperation, it only took about three days for the crews to clear out the damaged tower structure, erect the temporary wood poles, and rehang and energize the line.

While the power is now back on, the transmission linemen and contracting crews still have work ahead of them. For example, they must rebuild permanent transmission towers. As soon as the crews get access to the necessary materials, they plan to replace the transmission assets.

An EF-1 tornado caused this 345-kV tower to bend at its foundation and fall across the easement.

As a concerted effort, the crane on the far left holds the structure while crews work from the center cranes to remove small sections of the damaged tower. The crane on the far right held the conductor while the crews worked


Distribution Damage

In addition to the transmission system, the four tornadoes also damaged the distribution infrastructure. The tornadoes started in the center of the city, just west of a market. Three smaller tornadoes then sprouted behind the main twister and tracked northeast, where they inflicted the worst of the damage.

Overall, CPS Energy reported 290 cases of wire down. And 90 poles and crossarms, 90 transformers and 10,500 ft of wire were completely destroyed and had to be replaced. High winds from the tornado snapped distribution poles in half and pushed some of them so far sideways that they were no longer useable. By replacing the damaged wood poles with other wood poles, the crews were able to restore power more quickly.

Within 90 minutes, the storm had torn through San Antonio. As the crews were waiting for the storms to pass, outage calls were coming into the system operation center. The utility was watching storms pass on the screen, and it was deploying crews behind the storm.

As soon as they got the green light, the linemen were at the service centers, ready to roll out to the storm-stricken zones. After assessing the damage, the distribution crews, troublemen and system operators sprang into action to restore power for schools, homes and businesses. From the moment they were ready to go out on the restoration effort to the time the last customer was restored, it was only 48 hours.

To restore power that quickly, CPS Energy sectionalized its system and repaired power. The crews focused on the backbone feeders first and then cleared lateral lines on a systematic basis. By using this approach, the crews were able to drop the number of affected customers from 48,000 to 17,000 in just 12 hours. In the last 24 hours of the restoration, the crews focused on clearing tree limbs, replacing transformers and restoring service in the heart of its service territory. Going forward, the crews are working on replacing non-critical infrastructure such as streetlight poles, which were also damaged by the tornadoes.

In addition to 25 of its own distribution crews, CPS Energy also called upon contractors to help with the distribution work including T&D Solutions, Pike Electric and Chain Electric. The contracting crews worked alongside the utility crews to help replace poles, rehang wire and restore power as quickly and safely as possible.

Linemen clear transmission conductor from distribution poles and lay it on the guard structure shown in the foreground.

As a result of this focus on productivity and safety, CPS Energy did not experience any safety incidents during the storm restoration. To ensure that the linemen worked safely, the community came to their aid. For example, one night, when the line crew rolled into a residential neighborhood, the neighbors shone their flashlights on the poles so the crews had enough light to work safely.

The linemen often work long hours in difficult conditions, and CPS Energy’s customers showed their appreciation for their hard work and commitment to keeping the lights on through both typical and severe weather conditions. ♦

Rudy Garza is the senior vice president of distribution services and operations for CPS Energy, responsible for overseeing the service centers and the emergency management center. Garza, an electrical engineer, also manages the troublemen and line crews at CPS Energy.

Paul Barham is the senior vice president of electrical delivery service and manages the transmission, substation and engineering group at CPS Energy. He is a mechanical engineer with experience with power generation and energy delivery.


 

 

 

TAGS: Transmission
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