Study On The Effect Of Transformer Recovery Inrush To Differential Protection

With the development of electric power system, high capacity and super voltage transformer is used more commonly. The status of transformer become more important in electric power system, and the requirements to differential protection performance of transformer are becoming higher. First, establishing the mathematical model of transformer, this paper analyzes the characteristic of transformer recovery inrush and the effect to differential protection while the CT is good, propose a solution to this problem; And then the CT transient saturation model under external faults has been analyzed in detail and indicates that CT saturation and CT local transient saturation result in mal-operation of differential protection while fault is removed. After the research on the crucial problems of mal-operation in recently years, a cubic curve-fitting in the mal-operation region is proposed. This scheme could avoid the mal-operation of the different protection due to CT partial transient saturation during the removal of external fault.