Southwestern Power Administration (Southwestern or SWPA) energized a new autotransformer at its Nixa Substation on December 2, 2021 to improve electric reliability in Southwestern's footprint and to support the regional electrical grid as a whole.
The new 80-megavolt-ampere (MVA) autotransformer replaced existing 20-MVA autotransformer No. 1, which had been identified as having the potential of being overloaded during certain contingency events.
"We replaced the autotransformer because planning studies have shown that the replaced 20 MVA Nixa Autotransformer No. 1 could be severely overloaded if the 70-MVA autotransformer No. 2 experienced an outage during high loading conditions," explains Patrick West, who acted as Project Manager for the replacement and is an Electrical Engineer in Southwestern's Division of Transmission Engineering and Planning.
West explains that the single contingency analysis identified Nixa Autotransformer No.1 to be replaced by Summer 2022 to avoid further operational issues, so it was especially important that the autotransformer be in place and energized well before that deadline.
Springfield Regional Maintenance Manager Scott Sims agrees, noting that Southwestern maintenance personnel had been working toward the replacement of the autotransformer for some time.
"This project has been in the works for at least two years," says Sims. "There have been loading issues in the past, and my predecessor Marty Smith (who retired from Southwestern in July 2021) worked hard to get things in place for this project. I've been able to continue his work and help get it to the finish line."
Sims and West both agree that the COVID-19 pandemic presented a unique challenge to the autotransformer project because Southwestern normally does an inspection at the factory of the core and coil assembly prior to the assembly being lowered in the autotransformer tank, which is referred to as the pre-tank inspection. However, at the height of the COVID-19 pandemic, Southwestern had to complete the pre-tank inspection via video conference. Hours of video inspecting the core and coil assembly proved difficult, but Southwestern's team of Sims, West, and Carlos Valencia, Director of Southwestern's Division of Transmission Engineering and Planning, did their best to overcome the challenges.
Fortunately, Sims, West, and Valencia were later able to inspect the exterior of the autotransformer, witness Doble power factor testing, and review drawings at the manufacturer's (WEG) factory in Mexico. During the factory visit inspection, Southwestern's team created a detailed punch list of items that needed to be addressed prior to the autotransformer leaving the factory. Some of these punch list items included revisions to the tertiary and control cabinet, additional support for gauge wires and nitrogen tubing, and improvements to the grounding. The factory visit inspection was critical to the success of the project because it avoided unnecessary delays during the installation/testing at Nixa Substation and provided a better product for Southwestern.
Sims and West were also aided in their efforts by personnel from Southwestern's Division of System Protection and Communications. Electrical Engineer Bryan Viles designed the system protection and controls for the project and oversaw installation of said components so that the benefits of the upgraded autotransformer could be realized and further contribute to regional reliability through system protection.
"Bryan and Scott, Southwestern inspector Randy Shearer, High Voltage Electrician Lead Curtis Hunt, and the whole Springfield Maintenance Crew did an outstanding job getting the equipment installed and providing inspection of the contractor's work," says Project Manager West.
"Scott's crew executed the switching procedures, installed new conduits, modified the bottom of the tertiary cabinet to allow for the connection of the tertiary cables, and installed jumpers from the autotransformer to the bus." West adds that in addition to completing the design of the system protection and controls, Bryan Viles also oversaw the installation of the control cable, completed the checkout of all the alarms and controls, and made the appropriate adjustments so that the new autotransformer will operate in parallel with Nixa autotransformer No. 2.
West points to Southwestern's interaction with the primary contractor, Native American Transformer Services (NATS), as another factor in the successful project. He says that issues encountered during the manufacture and installation of the autotransformer were resolved due to extensive coordination with NATS and that Southwestern will continue to monitor the autotransformer through periodic tests performed by Southwestern's Maintenance Crew.
West acknowledges too that the project was a long time in the making. "The turnkey contract was awarded to NATS in November 2019," he explains, "and we have been working since to get the autotransformer energized in time."
"All in all, it was a successful project," says West. "It took coordination among the Division of Transmission Engineering & Planning to plan, coordinate, and manage the project, Acquisition and Facilities Services to solicit and award the contract, Maintenance to inspect and provide installation assistance, and System Protection & Communications to make sure all the elements were in place to operate and protect the autotransformer. Great job to everyone involved."