直流偏磁对不同铁心结构和联结组别变压器感应电动势的影响

特高压直流输电系统单极运行会导致临近变压器出现直流偏磁现象,而变压器感应电动势会对电网电压产生重要影响。为了研究直流偏磁对不同铁心结构和联结组别变压器感应电动势的影响,本文将三相三柱式和五柱式变压器时步有限元模型与YNy和YNd连接的外部电路相结合,建立了能够反映不同联结组别和铁心结构的变压器场-路耦合模型。研究了变压器感应电动势和励磁电流的基波及谐波含量随直流偏磁程度的变化规律,揭示了感应电动势波形畸变率与铁心结构及联结组别之间的关系;最后通过实验验证了结果的正确性。结果表明,直流偏磁对三相五柱式变压器感应电动势的影响较大,采用YNd联结会减小感应电动势波形的畸变率;而直流偏磁对三相三柱式变压器感应电动势基本没有影响。

Influence of DC Bias on Electromotive Force of Transformers with Different Iron Core Structures and Winding Connections

DC magnetic bias will occur nearby transformers during the monopole operation of UHVDC transmission system. Meanwhile, the Electromotive Force(EMF) of transformers also affect the voltage of power grid. To study the influence of DC magnetic bias on the EMF of transformers with different iron core structure and winding connections, this paper established a field and circuit coupled time stepping finite element model of transformer by combining the time stepping finite element model of three-limb and five-limb transformer with electric circuit model of YNy and YNd winding connections. This paper observed the variation of excitation current and the EMF of transformers along with the degree of DC bias and revealed the relationship between Total Harmonic Distortion(THD) of EMF and the iron core structure, winding connections. The experimental results verify that DC bias seriously deforms the waveform of EMF of five-limb transformer while the deformity rate can be decreased in YNd winding connection and that DC bias has little effect on the EMF of three-limb transformer.