Influence of Direct Current Bias on Vibration Characteristics of Converter Transformer

A three-dimensional physical model of multi field coupling of converter transformer is built, the type of excitation source of the model is changed by using the field circuit coupling method, and the electromagnetic and vibration characteristics of converter transformer under the action of DC component are studied. With the increase of DC content, the excitation current waveform of converter transformer is seriously distorted. Correspondingly, the distribution of magnetic flux density of iron core is more and more disordered, and the value of magnetic flux density increases. Due to the magnetostrictive effect, the increase of magnetic flux density directly leads to the increase of force on the iron core. DC bias makes the harmonic components of excitation current increase at each frequency, and the distortion intensifies. The increase of DC content and harmonic in the winding increases the force on the winding. When the DC bias coefficient reaches 1, the iron core is close to saturation, and the force on the iron core increases slowly, while the increase of magnetic leakage caused by iron core saturation increases the force on the winding more violently. The displacement of iron core and winding increases with the increase of DC content, and the variation law is consistent with the force. With the increase of DC content, the loss of core and winding increases. After the iron core is saturated, more excitation current is required. As a result, after the DC bias coefficient reaches 1.0, the loss of iron core increases faster than that of winding.