Influence of Design and Operating Practices on Excitation of Generator Step-Up Transformers

The damage resulting from overexcitation of generator step-up transformers could have an impact on generator reserve requirements unless suitable steps are taken by the industry. This paper discusses transformer design theory relating to overexcitation, utility operating practices, and overexcitation experiences; also, an estimate is made of the probability of overexcitation occurrence for units rated 150 MW and larger. Automatic corrective action is recommended, and a logic circuit is presented to accomplish this objective.