Electromagnetic Characteristics of a Scaled-Down Single-Phase Four-Column Autotransformer Calculation Excited by DC Currents

Single-phase four-column autotransformer is the key equipment of the extra-high voltage power grid, and its safe and steady operation is directly related to the security of the power system. By using different DC voltage sources represents various strengths of transformer DC bias, this paper proposes an model that combines finite element magnetic field model and equivalent circuit model to investigate the electromagnetic characteristics of single-phase, four-column autotransformer excited by DC bias, which is field-circuit coupled model. A DC bias parameter that denotes the strength of transformer DC bias is introduced, the simulation results under different DC bias parameters show that when excited by DC, there is an enhancement in the magnetic flux density of the core, and the distortion of the exciting currents waveform, with the even harmonics most significantly increasing in amplitude. The conclusion drawn is that GICs can significantly increase the content of harmonics and magnetic flux density of the core.