特高压直流换流变压器的研制

Development of UHVDC Converter Transformer

结合向-上特高压直流工程换流变压器的技术参数和试验要求,重点分析所需研究的交流和直流电场分布、绝缘结构与散热、阀侧引线及出线装置等关键问题。在运输限界基本不变的前提下,换流变压器的阀侧试验耐受电压、直流偏磁耐受能力等要求均有较大提高。特高压换流变压器研制中应优化主、纵绝缘结构,合理控制场强分布,要充分考虑温度对直流电场分布的影响,提高绝缘强度,以保证换流变压器的绝缘可靠性;在运输条件允许的情况下,阀侧引线应尽量放置在油箱内部,减小现场安装的难度和风险,同时,阀侧套管和阀侧出线装置仍是设备制造瓶颈。

The basic structure for converter transformers of Xiangjiaba Shanghai project is single-phase, doublewinding, on-load tap changer and oil-immersed. Compared with converter transformers in ± 500 kV HVDC projects, withstand voltages of valve windings are higher. It is difficult to select insulation material to regulate the DC and AC voltage distribution. Furthermore, the coordination between insulation structure, the reasonable electric field strength on the interfaces of oil and insulation pressboards and transportation limits shall be more important in the design of converter transformer. As for the barrel system arrangement of valve windings, it is related to the transportation limits and assembly work on site. The internal barrel system structure of valve windings for converter transformers of Xiangjiaba-Shanghai project is selected. The DC bias current control also is crucial in converter transformers＇ design. In Xiangjiaba Shanghai project, the requirement for DC bias current is as much as 15 A per converter transformer, so the margin of magnetic intensity shall be enough in core structure design. As the acceptance required, the type/routine test is specified and also the corresponding coition is based on the IEC standards and special requirements of Xiangjiaba Shanghai project. Compared with converter transformers in±500 kV HVDC projects, test voltages of the DC applied voltage withstand test, polarity reverse test and applied AC voltage withstand are much higher.