In the digital renovation process of conventional substation

the circumstance may exist that CT and ECT mix in transformer differential protection. The problem needs to be analyzed that whether the circumstance would influence transformer inrush recognition to prevent differential protection’s disoperation. The analysis starts from transformer inrush current characteristics and identification criterion. Transfer characteristics of CT and ECT is simulated

and the harmonic content of differential current after the inrush is transferred under saturated and unsaturated CT is studied

the validity of the second harmonic restraint criterion is analyzed

the transformer inrush recognition problem in CT mashup is answered.