Influence of DC Bias on Winding Vibration of Converter Transformer under Harmonic Condition

Abstract

Aiming at the problem of abnormal vibration of converter transformer windings under direct current bias, combined with Maxwell's equations, Lorentz force and related formulas of structural mechanics, based on the finite element simulation platform, a three-dimensional model of converter transformer coupled with multi-physics was built. Considering the symmetric structure of the model, in order to shorten the calculation time, the model is divided into four equal parts to reduce the calculation amount. According to the actual working conditions, a model of the direct current transmission system is built to obtain the harmonic content of the excitation source in the actual operation of the converter transformer. Through the comparative analysis of the magnetic flux density, it is shown that if the harmonic condition is ignored and the excitation source is set to a standard three-phase sinusoidal voltage, the simulation results will have a large deviation from the actual situation. According to the changes of the magnetic field distribution, current magnitude, stress distribution and deformation of the windings before and after the addition of the direct current component, the vibration characteristics of the converter transformer windings under direct current bias are studied. The results show that under the direct current bias, the leakage flux density, current, stress and displacement have increased, and the vibration of the winding is intensified.