A level 3 tornado wiped out the only substation in Dumas, Arkansas. The disaster severely tested Entergy's construction division capabilities and presented many challenges to the line crew.
On a cold Saturday afternoon in February, while the rest of the Midwest was dealing with massive blizzard conditions, a tornado carrying winds up to 207 mph hit the city of Dumas head on. In a matter of seconds, the tornado injured 37 people and left two young children in critical condition. The tornado destroyed or damaged 40 businesses and 120 homes.
At the eastern edge of Dumas, the city's only power supply was a heap of twisted metal, barely recognizable as Entergy's energy substation. The tornado also left the community of 5300 southwest of Pine Bluff, Arkansas, without power. Entergy's response was swift and unprecedented, but the sustained urgency involved not only restoring power, but also building a new substation from the ground up.
The first order of business was to restore service to the 2700 customers in Dumas. Entergy Corp. delivers electricity to 2.7 million utility customers in Arkansas, Louisiana, Mississippi and Texas. Entergy Arkansas, which provides electricity to almost 673,000 customers in 63 counties, had never seen such substation devastation in the history of the company.
Entergy maintains a fleet of portable transformers including a new 50-MVA mobile substation. The utility was working out the logistics of mounting and transporting the large custom-designed unit when the tornado hit. The self-contained substation platform contains everything necessary to become a temporary substation all in one platform — main breakers, circuit switchers, relays and remote terminal units (RTUs). It is larger than the company's other temporary transformers.
The utility needed a way to restore and maintain power until a new substation could be built. For that reason, the utility deployed the mobile substation to Dumas as soon as possible. Part of the challenge was the fact that this was the first time the unit had been deployed strategically.
A site across the street from the damaged substation was designated as the site of the temporary transformer. It was located next to the 115-kV transmission line that ran directly overhead. While Entergy line construction crews and contractors began repairing lines and erecting temporary distribution circuits to the new temporary site, a team was dispatched to move the mobile transformer. At the same time, more than 100 linemen from Entergy Arkansas and Entergy Louisiana and contractors were working night and day to repair local business and residential distribution lines in Dumas.
On Tuesday, three days after the tornado hit, the temporary transformer substation was energized and power delivery was restored to all of the 2700 residents and businesses that could accept power.
Rebuilding From the Ground Up
With the temporary substation operational, the next challenge was to deal with the existing substation, which was barely recognizable and unsalvageable. With warm weather approaching along with peak load demands, Entergy set a June deadline for rebuilding the distribution portion of the substation. This was half the time required to build a state-of-the-art substation of this size. The utility determined that the focus of the rebuild needed to be the completion of the low side — the 13.8-kV distribution circuits, followed by a four-breaker ring configuration system and a new 115-kV capacitor bank — which had been destroyed by the tornado.
As the mangled steel, broken foundations and damaged equipment, wire and other materials were being cut up and removed, construction commenced. Engineers from Entergy's corporate office surveyed the existing footprint and began designing the new substation on the site.
As with any emergency restoration effort, procurement of equipment was a challenge. Fortunately, Entergy maintains an inventory of spare poles, wire and equipment such as transformers in the system for other projects and emergencies. These items were quickly identified and diverted to the Dumas Substation.
One of the persistent challenges of the fast-track rebuild was working simultaneously on multiple phases of the 260-ft by 330-ft substation construction site. In a normal substation build, workers complete the site, foundation and ground conduit work first and then work on setting the control house and other equipment structures. This is usually followed by the setting of equipment and wiring and the testing of circuits. AC/DC battery back-up systems and other miscellaneous tasks are also usually completed incrementally in phases. On this job, however, they were all going on at the same time.
The contractor who was building the foundations, grounding and conduit work would complete a small section, and then the contractor who was in charge of the electrical work would begin erecting steel, putting up structures, installing breakers on pads, putting up bus work, insulators and switchers, and installing the two transformers. The foundation crew would then move on to another section of the site.
At one point, 52 personnel were working on various phases of the project at the same time. Normally there would never be this many people inside a substation at the same time. Entergy's core value is never to compromise safety for urgency. To address this challenge, an operational coordinator led the entire construction project. From day one, this person was on site 99% of the time, coordinating the contractors and internal crews, organizing tailboard meetings every morning and making sure everyone knew what everyone else was doing.
Change of Scope Meetings
Each group of workers conducted a daily job safety/hazard analysis to review the crews' tasks, identify the potential risks and determine how to mitigate those risks. If the job had a major change in scope, the construction coordinator approached the foreman in each group, who then had a huddle meeting with his group to go over new hazards associated with the change.
For example, a 109,000-lb transformer was unexpectedly delivered a day early. This circumstance wasn't discussed during the morning tailboards, so the construction coordinator stopped the crews and talked about the hazards associated with the early delivery of the transformer. When the workers unloaded the transformer, they needed to know exactly what was going on at the substation.
Bringing a large vehicle and piece of equipment into the substation involved a rigging crew, a crane, a truck and a trailer in order to set up the transformer, unload it and set it on the pad. Dumas police also provided assistance with traffic control and vehicle safety for delivery. With temporary flagging, barricading and cranes in operation, everyone's job was affected. The goal was to keep everyone safe.
Throughout the project, everyone on the job was kept informed about what other crews were doing. When anyone new came on to the work site, he or she was pulled aside and given a safety orientation along with a briefing on what types of work were being performed by the various journeyman mechanics, operators, foreman, journeyman substation mechanics, senior relay technical, apprentice relay technicians and general craft personnel.
Protection and Control
One of the pivotal milestones of the project was when the control house was installed and made ready. Before Entergy puts any system into service, there has to be control and monitoring capability of that equipment. Once the foundation and conduit were in place for the control house, it was brought in from another substation project.
The control house contains all the relay protection and control monitoring equipment. This includes two transformer differential relay panels, transmission line relay panels, ac/dc systems, and supervisory control and data acquisition required to provide safe and reliable service to Entergy's customers.
To ensure that the system protection and control phase of the project was implemented correctly, a contractor crew, along with Entergy technicians, were charged with wiring, terminating, testing and checking the relay and control system. All cable related to system protection and control is run through the conduit into the control house. It is then hooked up to the relay panels and RTUs, metering and ac/dc circuits feeding the relay panels and breakers. All the battery systems also were installed and ready for service by the scheduled June deadline.
From the day the tornado hit, Entergy employees and contractors worked more than 20,000 man-hours rebuilding the site, all without an Occupational Safety and Health Administration recordable injuries.
A fast-track project would normally last only a few weeks during an emergency such as a storm-restoration effort. This project was done in half the time of a normal substation build, but still took four, at times grueling, months. April and May were unseasonably wet and rainy, followed by unbearably hot, humid working conditions. To mitigate the stress and fatigue, Entergy made every effort to find days off for the crews to rest and take care of personal matters.
In June, Entergy met its cutover deadline and removed the 50-MVA mobile substation. During that month, work also continued on the 115-kV transmission portion of the substation, which will be completed by the end of 2008.
While the tornado was a huge disaster for the Dumas community, one positive outcome is that the city now has a brand-new, state-of-the-art $10.8 million substation that will provide reliable electrical service for many years to come.
Paul Chamoun has worked for Entergy for more than 23 years. In 2002, he was appointed to the position of supervisor of Transmission and Distribution Construction for Entergy Arkansas. PCHAMOU@entergy.com