If the TA is saturated, the traditional second harmonic restraint program of Transformer differential protection in transformer load switching, internal or external fault removal cause the differential protection malfunction because the second harmonic content is low. The harmonic analysis is carried out for the differential current in the text. To some problems for the traditional second harmonic restraint, The new second harmonic restraint program is proposed based on the amplitude and phase of the second harmonic comprehensive criterion. The phase relationship between the fundamental and the second harmonic is researched in inrush current. The integrated brake criterion is constituted by the second harmonic restraint coefficient adaptively with the second harmonic content. The correctness and reliability of the proposed scheme is verified through a large number EMTP simulation.
