Abstract: For the no-load transformer operating in a 110 kV substation,the abnormal characteristics of magnetizing inrush current waveform output from the electronic current transformer（ECT）are analyzed.According to the transfer characteristic of lossy integrator in the protection current acquisition system of ECT based on Rogowski coil,the analytical expression of the relation between the time constant and the transmission error is derived.Thus an appropriate integration time constant is selected to achieve 5TPE level accuracy of ECT.A simulation model is developed based on the theoretical analysis.After waveform fitting,it is proved that the main reason of abnormal magnetizing inrush current waveform is the improper integrator time constant of ECT.Meanwhile,the simulation also shows that the ECT with a proper integrator time constant has better transient transfer characteristics.