How to distinguish inrush current and fault current is the inherent problem of transformer differential
current protection. At present the second harmonic restraint method is used to prevent misoperation on
inrush current. But statistical data show that the method faces the risk of misoperation [1]. In recent years,
many methods for discriminating inrush current have been presented. Most of those methods are based on
one aspect of the features of current waveform, such as the virtual third harmonic [2], the attenuation
factor of the harmonics [3], and the difference between the differential current waveforms in different