降温过程中油-纸绝缘微水析出动力学过程及其对绝缘性能的影响

Oil-paper insulation is main insulation form for HV, EHV and UHV large transformer. There is inevitably a certain amount of moisture in oil-paper insulation, and saturation moisture content at steady-state is strongly dependent on temperature. The cooling process can lead to moisture precipitation from insulating oil, and the precipitation process may be one of the reasons for low-temperature failure of power transformers insulated by oil-paper. Therefore, it is of certain scientific and engineering significance to study dynamic process of moisture precipitation from oil-paper insulation and its effect on insulation properties during cooling process. The project will experimentally study the change rule of moisture content in oil on the different spatial location with temperature or time during cooling process, as well as dynamic mechanism of the rule influenced by initial moisture content in oil, cooling rate and oil-paper proportion. Based on experimental results and moisture diffusion theory of oil-paper insulation, moisture precipitation from oil is modeled and simulated to ascertain dynamic mechanism and physical nature of moisture precipitation from oil-paper insulation during cooling process. Furthermore, corresponding variation of dielectric properties of oil-paper insulation is investigated and feasibility of characterization of dynamic process of moisture precipitation from oil-paper insulation with change rule of dielectric properties of oil-paper insulation is explored. The results will provide a theoretical and experimental basis for the design, operation and maintenance of oil-paper insulation equipments in the cold regions.

油纸绝缘是高压、超高压和特高压大型变压器的主要绝缘形式，其内部不可避免地存在微量水分，且稳态饱和微水含量强烈依赖于温度。降温过程中油内微水析出可能是油纸绝缘电力变压器低温故障的主要原因之一。因此，研究降温过程中油-纸绝缘微水析出动力学过程及其对绝缘性能的影响具有一定的科学和工程意义。本课题拟实验研究降温过程中油纸绝缘结构内不同位置处油中微水含量随温度及时间的变化规律，以及初始微水含量、降温速度、油纸比例对这一规律的影响，并根据实验结果及油纸绝缘水分扩散理论进行物理建模和仿真分析，探明降温过程中油纸绝缘微水析出的动力学机理及物理本质。同时，研究对应状态下油纸绝缘介电性能的变化规律，探索通过油纸绝缘介电性能变化表征其微水析出动力学过程的可行性。研究结果可为寒冷地区油纸绝缘设备的设计与运行维护提供理论指导与实验依据。

作为变压器的主要绝缘形式，油纸绝缘的介电性能和变压器的稳定运行紧密相关。由于油纸绝缘内不可避免地存在微量水分，且其稳态饱和微水含量强烈依赖于温度，所以水分和温度将严重影响油纸绝缘的介电性能。因此，研究降温过程中微水对油纸绝缘介电性能的影响及微水析出动力学过程具有一定的理论价值和工程意义。. 本研究利用自建的低温高压实验平台，对降温过程中不同条件下变压器油及油纸复合绝缘的介电性能进行了实验研究。结果表明：降温过程中，随着初始微水含量的增加，变压器油及油纸绝缘的电导率及损耗因数增大，击穿电压及局放起始电压下降；随降温速率的增加，变压器油及油纸绝缘的电导率及损耗因数增大，击穿电压及局放起始电压下降；在空间位置上，沿容器自上而下变压器油及油纸绝缘的电导率及损耗因数增大，击穿电压及局放起始电压下降；对于油纸复合绝缘，随油纸绝缘中纸板比例的增加，油纸绝缘的损耗因数增大，电导率、击穿电压及局放起始电压下降。上述结果说明，降温过程中油纸绝缘微水含量高引起介电性能下降是导致变压器绝缘故障可能因素之一。. 通过对降温过程中油纸绝缘微水析出过程的仿真分析发现：变压器油中空间各处的水分浓度随高度的降低而增大，水分沉降过程完成的时间随温度的降低而减少；温度降低，绝缘纸板中水分的含量和扩散速度也随之降低，达到平衡所需的时间增加。