直流偏磁对换流变压器励磁电流的影响

Influence of DC magnetic bias on excitation current of transformer

直流偏磁是换流变压器的一种非正常工作状态,是指在变压器励磁电流中出现直流分量,它使励磁电流显著增大及波形严重畸变,使变压器铁心在正、负两个半周内饱和程度不一致,即使铁心磁化曲线不对称,使铁心出现周期性的饱和.针对上述情况,提出了一种在直流偏磁情况下研究变压器空载的二维瞬态场路直接耦合有限元分析方法,分析了在不同直流偏磁情况下,变压器空载状态下的铁心磁感应强度、励磁电流情况.结果表明,随着变压器直流电流的增加,变压器铁心饱和度愈高、励磁电流畸变愈严重.

DC magnetic bias is an abnormal working state of a converter transformer, which means that the excitation current contains DC component. DC magnetic bias makes the excitation current rise obviously and magnetic field waveform distort seriously, which leads to different saturation levels in positive-half cycle and negative-half cycle. It makes magnetization curve of the iron core asymmetric and iron core saturate periodically. For this case, 2-dimensional transient finite element method coupled with circuit loop was adopted to study the no-load transformer on the basis of DC magnetic bias, which was used to analyze iron core magnetic flux intensity and excitation current in case of the no-load transformer on the basis of different DC magnetic biases. The results indicate that with increasing the DC of a transformer, the higher is the core saturation, and the more serious is the excitation current distortion.