Abstract: Currents through delta windings of transformers connected in wye-delta mode cannot be measured directly therefore line differential current is used to realize differential protection.The symmetry inrush current resulted from line differential current may invalidate the restrained criterion for inrush current.A method for calculating the current through delta windings utilizing the measured current from current transformers is proposed.With this calculated current the phase differential current can be obtained.Based on the method an adaptive secondary harmonic split-phase restrained scheme for magnetizing inrush current for transformers connected in wye-delta mode is presented.The scheme can greatly improve the performance of transformer differential protection because it can adaptively adjust the secondary harmonic ratio of restrained current,and guarantee the fast action when transformers with internal faults are no-load energized.Simulation results in MATLAB/Simulink validate the proposed scheme.