Abstract：For the converter transformer, the eddy current loss of the tank under DC bias will increase significantly, which will lead to the temperature rise of the transformer and threaten its safe and stable operation. Therefore, it is necessary to quickly evaluate the eddy current loss of the tank under DC bias. At present, given the particularity of the load current of the converter transformer, much research work has been carried out to study the relationship between the stray losses of the structural components corresponding to different harmonic contents. However, the research conclusions do not consider the impact of DC bias applied to the converter transformer. The research on the stray loss of tanks, pull plates, and other structural parts under DC bias is mainly based on AC transformers. Therefore, considering the characteristics of the nonlinear load current of the converter transformer, this paper analyzes the change of eddy current loss of the tank under DC bias. Firstly, the distribution of the magnetic circuit on the tank surface under different working conditions is analyzed. Combined with the actual nonlinear load current waveform and eddy current loss calculation formula, the influence of converter trigger angle and DC on the tank eddy current loss at the rectifier and inverter sides is obtained. According to the analysis conclusion, a loss ratio factor k is introduced, and a simplified formula for calculating the eddy current loss of the tank when the dc bias is applied is given. Then, the finite element simulation software COMSOL is used to build a finite element model of the eddy current loss of the tank of an 800 kV converter transformer. The field circuit coupling simulation is carried out with the external circuit of the primary and secondary sides of the converter transformer. The converter transformer tank current loss index under rated conditions has a small error compared with the value of the IEC standard, which also proves the correctness of the model to a certain extent. The simulation value variations of tank loss under DC bias, surface magnetic field, and eddy current distribution are also consistent with the theoretical analysis. Finally, two 380V transformers with a 1:10 structure scale are used to verify the theoretical analysis and simulation calculation. The main conclusions of this paper are as follows: (1) When DC bias is applied to the converter transformer, the eddy current loss of the tank can be expressed as the rated loss multiplied by the ratio factor k and the no-load DC bias loss. The coefficient is less than 1 and decreases with the increase of DC and trigger angle of the converter. (2) Under the same DC, the larger the trigger angle of the converter is, the smaller the eddy current loss of the tank. (3) When the converter transformer on the inverter side is DC-biased, the eddy current loss of its tank is generally larger than that on the rectifier side, so the converter transformer on the inverter side is more vulnerable to the DC bias.
黄天超, 王泽忠, 李宇妍. 换流变压器直流偏磁对油箱涡流损耗的影响[J]. 电工技术学报, 2023, 38(8): 2004-2014.
Huang Tianchao, Wang Zezhong, Li Yuyan. The Influence of Converter Transformer DC Bias on Eddy Current Loss of Tank. Transactions of China Electrotechnical Society, 2023, 38(8): 2004-2014.
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