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 developed to restart AEP´s Rockport Plant -- following the failure of the phase three 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.