特快速暂态过电压和雷电冲击下SF_6长间隙伏秒特性

Voltage-time Characteristics of Long SF_6 Gap Under VFTO and Lightning Impulse

为研究特高压气体绝缘开关设备(GIS)在特快速暂态过电压(VFTO)和雷电冲击(LI)下的SF6长间隙伏-秒(U-t)特性,设计了VFTO模拟产生装置。通过改变实验间隙距离、气压和电压种类,研究了不同气压下SF6棒-板和球-板长间隙在负极性VFTO和LI下的U-t特性。实验结果表明:球-板稍不均匀电场间隙在VFTO下的最小击穿电压高于LI下的,而VFTO下的U-t曲线较LI下的曲线平坦,导致2种电压下U-t曲线相交。对于高气压(0.5MPa)下棒-板间隙,VFTO下的U-t曲线位于LI的之下。基于对实验结果和U-t特性曲线物理意义的分析,得到了用于预测给定SF6长间隙U-t曲线的半经验公式,该公式为带有3个参数的幂指数函数,其中的待定参数可由气压、间隙距离和电场不均匀系数共同决定。校验结果表明:采用半经验公式预测的U-t曲线能准确反映SF6间隙击穿特性,从而为GIS绝缘设计提供参考。

In order to study the voltage-time（U-t} characteristics of SF6 long gap of ultra-high voltage{ UHV） gas insulated switchgear （GIS） under very fast transient overvoltage （VFTO） and lightning impulse （LI）, a generating system of VFTO and LI was designed. By changing the gap length, gas pressure, and voltage type, the U-t characteristics of rod-plane and sphere-plane SF6 long gaps under negative VFTO and LI were investigated at different gas pressures. Experimental results show that, although the minimum breakdown voltage of the sphere- plane gap under VFTO is higher than that under LI, the U-t curve of the sphere-plane gap under VFTO is flatter than that under LI, resulting in the intersection of U-t curves. However, for the rod-plane gap, the U-t curve under VFTO is below that under LI at the pressure of 0.5 MPa. Based on the analysis of experimental results and physical background of U-t curves, the semi-empirical formula is derived to predict the U-t curves of the given SF6 gap. This formula can be expressed by a power exponent function with three parameters, which are related with gas pressure, gap length, and field nonuniformity factor. It is demonstrated that the predicted U-t curves can reflect breakdown characteristics of SF6 gaps accurately, which is useful for insulation design of GIS.