复杂电场作用下换流变压器套管绝缘特性分析

Analysis on Insulation Property of Converter Transformer Bushing Under Complex Voltage

换流变压器套管是高压直流输电系统的关键设备之一,在运行中需要承受各种类型的电压作用。为综合考量换流变压器阀侧出线套管的绝缘特性,笔者建立某干式直流套管数值分析模型,利用有限元计算方法计算套管在不同类型试验电压作用下的电场分布,分析套管绝缘性能。结果表明:换流变压器套管在交流电压下电场呈容性分布,且在环氧树脂主绝缘内较为集中;在直流电压作用下电场呈阻性分布,且在SF6气体内较为集中;直流电场下介质中积累的电荷造成极性反转时套管内电场突变,环氧树脂和硅橡胶中的电场在反转后瞬间均出现峰值;伞群中部硅橡胶中的峰值场强达到了直流稳态值的22.32倍,会对套管绝缘造成极大威胁。

A converter transformer bushing suffers complex voltage in a high voltage direct current（HVDC）system. To comprehensively evaluate its insulation property, a numerical model is built to calculate the electric field distributions under different kinds of voltage with finite element method. Results show that： 1）under AC voltage the electric field distribution in the bushing is capacitive with potential contours concentrating in epoxy resin; 2）under DC voltage the electric field distribution in the bushing is resistive with potential contours concentrating in SF6gas; 3）the DC static voltage makes free charges accumulating on the surfaces of solid media to lead to a dramatic change of electric field distribution when the polarity reversal occurs, and a transient peak value of electric intensity appears in respective epoxy resin and silicon rubber after the polarity reversal; and 4）the peak value of electric field reaches up to 22.32 times of the static value in the middle of the shield, which will greatly harm the bushing＇s insulation.