DC bias computation study on three-phase five limbs transformer

作者：Li Xiao Ping^*; Wen Xi Shan

来源：Proceedings of the CSEE, 2010, 30(1): 127-131.

• AC transmission
• B phase
• Current harmonics
• DC bias
• Dc current
• DC transmission systems
• Electric circuit
• Magnetic intensities
• Neutral point of transformer
• Nonlinear algebraic equations
• Nonlinear characteristics
• Single phase
• Transformer core
• Two phasis
• Zero sequences

The DC current flows into the earth as DC transmission system runs in monopole. At the same time the DC current inrush the AC transmission system through the earthed neutral point of transformer, which result in DC bias of AC transformer and consequently harmonics are produced. In previous research, DC bias problem on transformers of single phase and three-phase three limbs had been studied and had got some regularities. In this paper, DC bias on three-phase five limbs transformer had been studied by calculation. In the process of calculation, Maxell formula was used instead of magnetic circuit formula, coupling with electric circuit, combining with nonlinear characteristics curve of transformer core. A series of mathematic transformation were performed and numerical nonlinear algebraic equations were solved finally. Meanwhile DC bias problem on three-phase five limbs transformer were analyzed. The reasons were that A and C phase is much more close to zero sequence magnetic circuit than B phase and the coupling extent of B phase with other two phases under DC bias become feebleness. The magnetic intensity of transformer core limbs was calculating synchronously. The magnetic intensity of end yoke is largest and that of side leg is smallest without DC bias. Under DC bias the magnetic intensities of end yoke and side legs are increasing fastest with the increase of DC bias.

• 出版日期2010