How Tapchanger Controls Contribute to Premature Transformer Failures

This paper focuses on LTC (load tap changer) transformer control practices, which may cause tapchanger hunting and therefore excessive tapchange operations. Applications of paralleling methods and the determination and confirmation of optimum settings, which may contribute to excessive or untimely tap change operations, are discussed. The transformer applications considered in this paper will include transmission tie transformers as well as transmission-distribution interface transformers. Attention will be drawn to common paralleling commissioning practices in the field that can create conditions for tapchanger "hunting." In many applications, a control function will result in different actions depending on the system configuration and parameters. These changing system conditions are continuously affected by automatic operations on the transmission and distribution systems, such as protective relay operations or load management techniques. Some of these system conditions will also be discussed.