Wind turbine generator step-up transformer failure investigation

This paper presents an investigation into the recurring failures of pad-mounted generator step-up transformers that have been experienced by Exelon Wind at a wind farm in Northern Texas. Observations indicate that the transformer failures are typically a result of contaminated oil due to arcing within the transformer expulsion fuse tube. To determine the underlying cause of this phenomena, S&C Electric Company installed digital monitoring equipment to capture electrical and thermal data at a pad-mounted generator step-up transformer over a four-month period. Electrical data was also captured at the point of interconnect between the wind farm and the local utility. The data captured in this time frame revealed that high-current surges and current cycling frequently occurred due to the WTG cycling on and off from the highly variable wind speeds in the area. High-current surges and current cycling places thermomechanical stress on the transformer and expulsion fuse links, which may ultimately lead to the types of failures experienced at this location.