高速动车组牵引变压器轻量化理论与方法研究

The lightweight of electric traction system has been admitted as a prospective development direction of high-speed EMUs (electric multiple units) in China. The OBTT (on-board traction transformer) is the heaviest single electrical equipment on EMUs. The OBTT with large weight has put a heavy strain on further increasing the speed of trains and caused irreversible degradation of key components of EMUs. Therefore, the lightweight of OBTT has been assigned as a top priority initiative. Superconducting transformers, power electronic transformers and light dry-type transformers are potential solutions to the lightweight of EMUs. Compared with the other two types of transformer, dry-type transformer has some advantages: for example, it can avoid the inherent hazards of the liquid nitrogen coolant, which is a necessity of superconducting transformers. Moreover, it can also overcome the inherent drawbacks of power electronic transformer as the main components of power electronic transformer may not be able to withstand continuous overvoltage. However, due to the limitations of winding electrical properties, core magnetic properties and insulation thermal performance, existing dry-type transformer manufacture is hard to meet the loading capacity requirements of EMUs. There is still plenty of leeway to reduce the weight of windings and core of the dry-type transformer. To solve the above limitations, the project aims to develop a series of key components of OBTT including the high-conductivity high-strength windings, high-magnetic-density low-loss cores and high-thermal-conductivity high-thermal-resisting insulation system. Moreover, it will also explore the optimal coordination strategy among the above three key components and the corresponding electric system (i.e., traction power supply network and load). The whole project will be conducted by following a clear and systematical roadmap of mechanism exploration, material fabrication, performance evaluation and coordination validation. The outcomes of this project will open up a new theory and methodology for the lightweight OBTT development with an ultimate goal to significantly reduce, by a conservatively estimated 50%, the whole weight of existing on-board transformers (including accessories).

电力牵引系统轻量化是我国高速动车组既定的发展方向，车载牵引变压器是其中单体最重的电气设备，其重量已严重限制列车进一步提速，同时导致关键部件的提前劣化，因此轻量化已是当务之急。超导变压器、电力电子变压器和轻型干式变压器是潜在的轻量化方案，干式变压器可以避免超导变压器液氮冷却剂固有的安全隐患，也能克服电力电子变压器主要器件无法承受牵引网持续过电压的固有缺陷。但受限于常规绕组电性能、铁心磁性能、绝缘热性能，既有干式变压器技术难以满足装车容量需求，且其绕组和铁心有大幅减重空间。为此，本项目拟通过机理剖析、材料制备、性能测试与匹配性试验，研究高导电率高强度绕组、高磁密低损耗铁心、高导热高耐热绝缘，探寻“高导电绕组—高磁密铁心—高导热绝缘—外围系统（牵引网和负载）”的最优匹配方法，从而突破干式车载牵引变压器轻量化的理论与方法，力求整体重量比既有车载变压器（含附件）轻约50%。

车载牵引变压器作为电力牵引系统中单体最重的电气设备，其重量已严重限制动车组进一步提速，同时导致关键部件的提前劣化。干式轻量化是潜在的最可行的方案，但既有干式变压器技术难以满足装车容量需求，且其绕组和铁心有大幅减重空间。为此本项目通过突破绝缘导热、散热和整体优化设计等难题，实现了干式车载牵引变压器的轻量化设计。具体研究内容包括：1）构建了车载牵引变压器“电-磁-力”多物理场耦合的精细化三维模型，探究了不同运行工况和短路冲击下车载牵引变压器电、磁场分布特征与电动力分布特征，找出了绕组受到最大电磁力的数值与位置。2）通过分子模拟与实验手段相结合制备出基于六方氮化硼三维导热网络的高导热环氧树脂，相比既有绝缘热导率最高可提升138%。提出了基于液体橡胶吸能网络的高导热环氧树脂力学性能提升方法，结合绕组最大短路电动力对配方进行了筛选，保证绝缘能够承受短路电动力的冲击。3）通过电场-磁路耦合建模得到了各层级的边界磁通密度，解析了二阶麦克斯韦时准静态场方程组，获取了较为精确的截面电磁分布函数，构建了渐变截面宽度与磁场强度、涡流密度的动态耦合关系，明确了卷绕方式、带材形状对变压器铁心磁场、涡流及其损耗的影响机制，实现了大型卷铁心涡流损耗的解析计算。4）基于冷却流体及绕组间的耦合传热，以绕组线饼中单匝导体为基本单元进行传热分析，构建了由热流量、传导及对流热阻等参数关联组成的热网络传热模型，可实现绕组整体温度分布计算及热点定位，为多参数下散热结构优化设计及绝缘匹配研究提供高效工具。5）提出了基于中心复合试验设计和响应面法的干式车载牵引变压器多约束下的优化设计方法，基于所得轻量化优化设计方法，联合厂家完成了样机研制，实现了相比同容量油浸式车载牵引变压器减重约50%的目标。研究过程中取得以下成果：培养博士研究生10名、硕士研究生12名，发表SCI论文28篇、EI论文13篇，录用SCI论文1篇，授权发明专利19项。