Unbalanced GSU Transformer Configuration at Rockport Plant???Analysis and Operating Experience

This paper describes extensive engineering studies carried out at the American Electric Power (AEP) Service Corporation to determine the feasibility of operating a 1300-MW generating unit with an unbalanced generator step-up (GSU) transformer bank. These studies served as a basis for plans to restart AEP´s Rockport Plant???following the failure of the phase 3 GSU transformer on December 17, 1985???with the two remaining single-phase GSU transformers and a dissimilar spare transformer. The GSU transformer failure at Rockport created a unique and complex problem because the only spare transformer available for installation was of a design with which AEP had previously experienced problems. The limitations of the spare transformer resulted in a highly unconventional operating mode for the Rockport generating unit.