Translated Abstract
As a key equipment of HVDC transmission system, the ± 800kV UHV converter transformer plays a linking role connecting the AC and DC transmission systems, and its operational reliability is critical to the security and stability of the power system. The insulation structure of the UHV converter transformer is complex, its valve winding withstands the AC, DC, combined AC-DC, DC reversal polarity voltage and so on，and the internal insulation withstands a long-term combined effect of electric, magnetic, thermal field. Therefore, carrying out research on the insulation structure optimization of ± 800kV UHV converter transformer has great significance for improving operational reliability of the converter transformer, realizing independent design and localization of UHV converter transformer in our country.
In this paper, a UHV converter transformer used in ± 800kV UHVDC transmission system was taken as research project, its 3-D finite element simulation model was built by ANSYS, and the meshed method considering the skin effect in conductor eddy zone was studied, the electromagnetic field distribution and eddy current loss distribution of the converter transformer before and after applying the shielding were calculated, after that, the structure of copper shield on tank and shielding tube of AC lead were optimized, the optimization result passes the converter transformer temperature rise test verification. Then the insulation structures at the ends of valve winding were studied, and the allowable electric field strengths of converter transformer insulation structure under different operating voltages were selected, in addition, a reliability evaluation method of transformer insulating oil and oil-paper interface based on the volume effect was put forward. Based on this method, the IQDA was used to optimize the end insulation structures of converter transformer valve winding, and then the optimized insulation structure was checked if it meets the allowable electric field strength under the DC, AC conditions. The evaluation results show that the optimized structure meets the requirement of the control value.
With the research about the insulation structure optimization of ±800kV UHV converter transformer, this thesis provides a theoretical basis for the design of domestic transformer, Furthermore, the achievements have a practical value in enhancing the design autonomy and the international competitiveness of domestic UHV converter transformer.
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