Study On Mechanism And Prevention Of Transformer Differential Protection's Error Action

With the advance and the unceasing development of electric power system, the requirements of differential protection is becoming more and more high for transformer. After the research on the crucial problems, which have the influence on the digital differential protection, the method is presented to solve the protection's error action while outer fault removing. First, establishing the mathematical model of transformer, this paper analyzes the characteristic of transformer recovery inrush and indicates itself cannot result in mal-operation of differential protection while the CT is good; 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. Based on the analysis, a new method ,which is in other to determine the length of delay protection on the size and variations of differential current when the action point moves to the action district, is proposed to prevent the mal-operation of differential protection while fault is removed.