变压器油纸绝缘系统中的空间电荷现象

Space Charge Phenomenon in Oil-paper Insulation System of Power Transformer

特高压直流输电技术的发展对换流变压器绝缘系统的性能及安全稳定运行提出越来越高的要求,而空间电荷问题是影响和制约变压器油纸绝缘材料耐电强度,导致其老化和破坏的重要因素。针对换流变压器开展在交直流复合、极性反转等复杂电场作用下的空间电荷相关机理和试验研究具有重要的理论价值,而且对工程实际中的绝缘结构设计、材料制备与生产工艺亦具有指导意义。为此,针对近年来国内外油纸绝缘领域中有关空间电荷方面的研究成果和进展予以阐述和评价。在变压器油流注放电发展过程的数值仿真方面,国外学者通过数学、物理模型的建立,得到了随时间快速推移的场强与电荷浓度波峰,这是变压器油中流注发展的标志性现象。在电声脉冲法测量空间电荷方面,国内学者通过不同场强、湿度和老化程度下油纸绝缘介质中的空间荷特性,确定了载流子的类型、迁移率、陷阱深度,并引入量子化学方法计算得到油纸介质的分子能态密度,这是今后对微观与介观深入研究的重要方向。在复合电场条件下非线性与各向异性电场与空间电荷仿真方面,现有计算方法较为成熟。如何建立更为准确、完整的模型以得到更为符合实际的结果,则是今后的发展方向。

The development of the ultra-high voltage（UHV） direct current（DC） electric power transmission technology brings more challenges and requirements to the performance,safety and stability of the converter transformer insulation system.Space charge phenomenon is one of the key factors which influence and limit the voltage withstand capability of the oil-paper insulation.It is also an important cause of the insulation degradation and breakdown.Therefore,the mechanism and experimental study on the space charge phenomenon that exists in converter transformer under complex voltage forms,such as AC-DC composite voltage,polarity reversal voltage,etc.,are valuable to the theoretical domain.Furthermore,these studies will play a significant role in providing directions for the processes of insulation structure design,material preparation and manufacture techniques.This paper describes and evaluates the recent achievements about space charge related problems in the field of oil-paper insulation from both domestic and abroad.Foreign researchers obtain the results of fast migration of electric field and charge concentration peaks by establishing mathematical and physical models.The fast migration peaks are representative phenomena of the streamer developing process in transformer oil.In the aspect of space charge measurement with pulsed electro-acoustic method,domestic researchers determine the carrier types,mobility and trap depth by studying space charge characteristics under different electric field,humidity and degradation levels.Quantum chemistry method is adopted to calculate the molecular density of states of the oil-paper insulation,which signifies the future direction towards in-depth research in microscopic and mesoscopic scales.For the nonlinear and anisotropic electric field and space charge distribution simulation under composite electric field condition,the corresponding numerical method is mature.The future direction is how to establish a more accurate and complete model to obtain a more realistic results.