计及温度-电场强度非线性的换流变压器瞬态电场影响分析

Study on Transient Insulation Condition of Converter Transformer Based on Nonlinearity Between Temperature and Electric Field

换流变压器在运行过程中承受高电压,内部绝缘系统的温度高、电场强度大,耦合现象明显,而传统绝缘设计手段并未考虑非线性绝缘特性。首先该文搭建三电极实验平台,分析绝缘油及油浸纸板在不同温度、电场强度下的耦合现象。实验结果表明绝缘材料的导电性能受温度、电场强度的影响较大,其中绝缘油以2kV/mm为拐点,电导率呈先下降再上升的U型非线性曲线。其次,该文建立了含绝缘层、角环、垫块等完整的换流变压器耦合计算模型,分析了绝缘系统受温度-电场强度影响下的瞬态电场。结果表明:换流变压器内部温度变化较大,最大温升达68.7K,并且温度集中的区域紧邻电场强度较大的端部,因此耦合现象不容忽视。最后,对比极性反转过程中的瞬态电场,相比传统认为的指数型变化,考虑U型电场强度非线性下的油浸纸板最大电场强度增加1.7kV/mm;考虑温度-电场强度非线性时,不仅绝缘状态发生改变且油浸纸板弛豫时间降低。

Converter transformer bears high voltage during operation,and the internal insulation system has high temperature,large electric field intensity and obvious coupling phenomenon.However,the traditional insulation design method does not consider the nonlinear insulation characteristics..First,a three-electrode experimental platform is constructed to analyze the coupling phenomenon of insulating oil and oil-immersed paperboard at different temperatures and electric field intensities.Results indicate that the electrical conductivity of insulating materials is greatly affected by temperature and electric field intensity,in which the inflection point of insulating oil is 2 kV/mm,and the electrical conductivity presents a U-shaped nonlinear curve that first decreases and then increases.Then,a practical converter transformer model is built with refine insulation layer,collar ring and spacer to calculate transient insulation condition with the effect of temperature and electric field.It indicates that converter transformer has larger temperature range and the maximum temperature growth can be up to 68.7 K,meanwhile the concentrated temperature area is next to the larger electric field region,so a strong coupling phenomenon cannot be ignored.Under polarity reversal condition,the maximum value of pressboard electric field with U-type electric-dependence increases 1.7 kV/mm compared with exponential variation,and reaction rate would decrease in taking nonlinearity between temperature and electric field into account.