A current-based solution for transformer differential protection - Part I:Problem statement

This paper analyzes the problem of transformer differential protection. Fir st, we review the concept of transformer differential protection. We then a nalyze magnetizing inrush, overexcitation, and current transformer (CT) sat uration phenomena as possible causes of relay misoperation. Finally, we sum marize the existing methods for discriminating internal faults from inrush and overexcitation conditions. In Part II of the paper, we propose a new ap proach for transformer differential protection and describe the relay that is based on this approach.