气体绝缘开关设备（GIS）进出线套管处的电磁模型对特快速暂态过电压（VFTO）、暂态外壳电压（TEV）以及外部瞬态空间电磁场的建模计算有重要影响。特高压GIS系统的VFTO频率最高可达100MHz，此时套管屏蔽层导体的长度与电磁波波长可比拟，不能再用集总参数对套管建模。建立了具有双层屏蔽导体的特高压GIS复合套管宽频等效电路，分别采用传输线理论、分段传输线的级联和近似公式建立套管的三导体系统间均匀段、尺寸渐变段的双导体和导体间电磁泄漏阻抗的模型；用集总电容来等效导体尺寸不连续处激发的电磁波的高次模对主模传输的影响；分别提取套管顶部均压环、中间屏蔽层的对地电容，提取套管顶部均压环对中间屏蔽层的部分电容。综合上述传输线及各个部位的阻抗模型，计算1~100MHz频率范围内，从套管底部看进去的输入阻抗，并与全波电磁仿真的套管三维输入阻抗对比，二者一致性较好。%AbstractElectromagnetic model of bushing of gas insulated switchgear (GIS) is very important for the simulation of very fast transient over-voltage (VFTO), transient enclosure voltage (TEV) and transient electromagnetic field. The VFTO can contain frequency components up to 100MHz. At such high frequencies, the length of the inner shielding conducting layer is comparable with the wavelength and hence the bushing can not be modelled as a lumped parameter element. The broadband circuit model of a gas insulated bushing with double layer shielding is investigated. The three-conductor system of bushing is modeled using transmission line theory. The influence of high order modes of electromagnetic waves excited in the discontinuities of bushing on transmission of the main mode is treated as a lumped capacitance. The two-conductor with tapered size is considered as the cascading of multiple segments of transmission lines. The electromagnetic leakage from bushing is handled with by using a radiation impedance obtained from the approximate formula. The ground capacitance parameters of top grading ring and the middle shielding layer as well as the capacitance parameter between top grading ring and the middle shielding layer are extracted respectively, by using numerical computation method. The input impedance observed at the bottom of the bushing is calculated using the circuit model of transmission line and impedance model built above within the frequency range from 1MHz to 100MHz. The results from the broadband circuit model are in good agreement with those from the 3D full-wave simulations solver CST-MWS.
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