Abstract: There may be high-amplitude zero-sequence inrush generated by a high voltage built-in high-impedance transformer in the process of no-load closing. The zero-sequence inrush will distribute in the line and may cause the maloperation of the line zero-sequence over current protection. In addition, the above phenomenon exists when a spare transformer is put into operation, and the automatic device transfer operates unsuccessfully. In order to solve this problem, the characteristics of zero-sequence inrush are studied based on the formula of zero-sequence inrush in this paper. The dead angle and second harmonic of zero-sequence inrush are calculated and analyzed. On this basis, the feasibility of a dead angle and second harmonic breaking criterion to identify zero-sequence inrush is analyzed. The results show that the dead angle of zero-sequence inrush reduces so significantly compared with phase inrush that it cannot be regarded as a characteristic to identify zero-sequence inrush. The second harmonic component increases obviously, so the second harmonic breaking criterion is an advisable scheme to ensure that automatic device transfer is put into operation successfully. Finally, a simulation test based on PSCAD/EMTDC verifies the accuracy of the analysis results.