Main transformer replaced at Synfuels Plant during half-plant turnaround

The main transformer at Dakota Gasification Company's Great Plains Synfuels Plant was replaced during the plant’s half-plant turnaround in May and June.

In May 2018, the transformer failed, tripping the plant. An internal component in the transformer caused contamination, which caused an internal arc and took the transformer out of service for more than a month, according to Chad Kuntz, Basin Electric supervisor of electrical engineering.

The transformer was put back into service but was not recommended for long-term service. “We did an analysis and decided that two transformers should be replaced,” Kuntz said. “When a transformer trips, it reduces available load to the plant. Subsequently, there may be a cascading series of shutdowns throughout the plant. There is a substantial risk of damaging equipment in this type of event and it takes a lot of time and work to fully recover.”

The Synfuels Plant was in a two to three week half-plant turnaround while the work was completed. The short timeframe for the work, with the transformer outage being one month long, added to the unusual circumstances of the job, Kuntz said. “Usually, we install a transformer on a new facility where we have time to place them, test them, and then the facility is energized. In this case, it was an operating facility, still operating at half-plant capacity, and so while the opportunity was there to do the work, there was risk in that we could cause a trip which would take the plant off completely,” he said.

The new transformer was purchased in 2019, and the Synfuels Plant’s 2020 outage was delayed a year due to the COVID-19 global pandemic. “We worked with a lot of areas to coordinate this work. We coordinated with the Synfuels Plant on their outage schedule, a heavy-haul contractor on site to move a transformer that weighs 250 tons, design done on the engineering side, Transmission System Maintenance out of Beulah did a lot of work testing the transformer and some other high voltage work that was associated,” he said. “So lots of people coming together to make this happen.”

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