复杂运行条件下换流变压器油纸绝缘在复合电场作用下的击穿及沿面闪络特性研究

The converter transformer is one of the key equipments in HVDC power transmission system, and its reliability will directly effect the safe operation of power system. The valve side windings of the converter transformer withstand not only AC voltage, lighting impulse voltage and switching overvoltage, but also DC superimposed AC and polarity reversal voltage. Existing research results and operating experiences show that the operation conditions, such as moisture content, temperature, oil streaming electrification and particle contamination in oil, have great influences on breakdown characteristics and mechanism for oil-paper insulation in converter transformer. According to real insulation structure in converter transformer and complex operating conditions that may occur during operation, this project will systematically carry out the research work on the breakdown and flashover characteristics with typical oil-paper insulation under complex voltages considering the operating conditions, such as moisture, temperature, oil streaming electrification and particle contamination. Through the experimental phenomena observation by different means, the influence mechanism of the different conditions on breakdown and creepage flashover characteristics under complex will be explored. The aggregation behaviors of space charge and fiber particle on cardboard surface under the oil flow driving, and its influence on creepage flashover characteristics for oil-paper insulation will be studied. The physical and mathematics models will be built to explain the experimental phenomenons above. The goal of the project is to provide theoretical and data references for design, manufacture and operation of the ultra-high voltage converter transformer to ensure its safe operation.

换流变压器是特高压直流输电系统中的重要设备，其运行可靠性直接影响系统的安全运行。运行中的换流变压器绝缘不仅承受交流电压、雷电冲击和操作过电压作用，还要承受交直流叠加和极性反转电压作用。已有的研究和运行经验表明，含水率、温度、油流带电及油中杂质等运行条件对复合电场下换流变压器油纸绝缘击穿特性及机理有着重要的影响。为此，本项目结合换流变压器实际结构及可能出现的复杂运行条件，在综合考虑含水率、温度、流油带电及油中杂质聚集等因素下，系统地开展典型油纸绝缘结构在复合电压下的击穿及沿面闪络特性的研究，并通过不同手段的试验现象观测，探索不同运行条件对复合电场下油纸绝缘击穿及沿面闪络特性的影响机理；探明油流驱动下空间电荷及纤维杂质在油纸绝缘中的聚集特性及其对沿面闪络特性的影响规律，建立用以解释试验现象的物理与数学模型，以期为特高压换流变压器设计、制造和运行提供理论与数据参考，保障换流变压器的安全运行。

换流变压器是特高压直流输电系统中的重要设备，运行时其将承受交流电压和交直流叠加等复合电压，且含水率、温度、油流带电及缺陷杂质等运行条件对复合电场下换流变压器油纸绝缘击穿特性有着重要的影响。为此，本项目结合换流变压器实际结构及可能出现的复杂运行条件，系统地开展典型油纸绝缘结构在复合电压下的击穿特性的研究，探索不同运行条件对复合电场下油纸绝缘介电特性和击穿特性的影响规律。研究结果表明：（1）温度和含水率对油纸绝缘电阻率、空间电荷和电场分布具有较大的影响，随温度及含水量的增加，变压器油和浸油纸板的体积电阻率均按指数规律下降；温度升高将导致纸中电场强度下降和油中电场强度上升，随含水量增加油中场强上升、纸中场强下降；绝缘纸板内空间电荷随温度升高呈先上升后下降趋势；（2）随着温度降低，低含水率变压器油击穿场强呈上升趋势，高含水率变压器油击穿场强则呈先降低后升高的趋势；变压器油击穿场强随外施电压直流含量增加呈下降趋势，油浸纸击穿场强随外施电压直流含量增加呈上升趋势。随着温度的降低，低含水率油浸纸的低直流含量击穿场强呈上升趋势，高直流含量击穿场强呈下降趋势；而高含水率油浸纸的击穿场强随温度降低呈上升趋势。油纸复合绝缘击穿电压随外施电压直流含量增加呈先升高后下降的趋势；（3）变压器油流速度对油纸绝缘油流带电和击穿电压具有较大影响，不同交流含量电压下冲流电流均随流速升高而增大，直流电场使起电层区域扩大，导致油流带电程度随外施电压升高而增大，且随着直流电压分量的增加，冲流电流出现饱和；油流带电使油纸界面空间电荷量增大，畸变了纸板和油中的电场分布，使油纸复合绝缘击穿电压随交流含量上升在不同流速下均呈先升后降的趋势；（4）在直流和交直流叠加电压作用下，绝缘油击穿电压都随纤维浓度增加而降低，整体上交直流叠加下的击穿电压比直流电压作用下的击穿电压高，且随纤维浓度增加下降幅度减小。