Study On Transformer Differential Protection Based On Waveform Symmetry Elements

Because of the importance of power transformer differential protection and the complexity of inrush current ,the study on magnetizing inrush current is furthered more and more by relay protection workers. Aiming at the faultiness of second harmonic brake principle and dead angle principle, the paper analyzed carefully the form and characteristics of inrush currents of single-phase transformer and three-phase transformer. Based on this, a deep study is done on waveform symmetry principle ,moreover, the paper anatomied some questions that exists in the practice, for example ,the infection of direct current, the determination of K,etc. The paper also gives an instance to realize this protection and explains its software and hardware in details.