Harmonics study for three-phase transformer under DC inrushing

In this paper, the circuit model of three-phase transformer with three-legs under DC inrushing is set up. Considering the magnetic coupling of three legs, the nonlinear single-value curve of one leg of transformer is deduced. Combining the circuit equation and nonlinear B ~ H curve of one leg of transformer, we gain the wave and harmonics distribution of exciting current. Because of magnetic coupling among three legs, although the winding of transformer have DC current, DC flux doesn´t exist in the legs of three-phase transformer. So the DC current inrushes the winding of symmetric have little influence on the exciting current, but increase heat loss