A transformer with a digital integrator will produce deformed waveforms while ransferring high-frequency current generated in the transient process of the power system

resulting in misoperation of the relay protection system. We established mathematical models of elements in the transformers with disparate types of integrators

and analyzed their transfer characteristics and the transfer process of high-frequency signals from the line current. It is concluded that the frequency of high-frequency current signals overlaps in the sampling process. Output low-frequency signals from the sampling process are enlarged compared with high-frequency ones in the following integrator and then mixed with the original signals

which accounts for the distortion output signal waveforms from the transformer with a digital integrator. In contrast

the transformer with an analog integrator works well in such situation. Actual experiments have been performed to verify the analyses. In addition

improvement approaches are proposed regarding the filter and sampling frequency to solve this issue for the transformer with a digital integrator.