## 2 Structural Parameters and Simulation Model
### Model Analysis and Accuracy Illustration  
It is necessary to understand the structural dynamical characteristics before conducting the seismic performance analysis. As expected, due to its suspension structure, the filter capacitor exhibits an obvious geometric nonlinearity. The main reason is the hinge joints between the suspended insulators of the layers. Because of such a flexible structure, it shows dramatically lower vibration frequencies than the steel door-type gantry. The earliest mode related to the steel gantry is the 23 rd mode that displays a coupling vibration of the filter capacitor and the gantry. The corresponding frequency is 1.78 Hz. The first three vibration modes of the structure with a pre-tension force of 20 kN are shown in Figure 5. The vibration mode information and effective mass are summarized in Table 2.  
The first two mode shapes are the horizontal bending of the capacitor and they have the same frequency of 0.181 Hz, showing the low vibration frequency and bending stiffness. Furthermore, the structural deformation nonlinearity also can be found in Figure 5. Reference [29] investigated an \(\pm\)800 kV coupling filter circuit and the fundamental period of the suspended filter is 5.556 s, that reflects a natural frequency of 0.180 Hz. The simulation model of this type of suspended filter was also validated by on-site hammer tests in the authors' other publication [44]; thus, the frequency results could be regarded reliable. The  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Order**} & \multirow{2}{*}{\
\begin{tabular}{c} **Frequency** \\ **(Hz)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Mode** \\ **Shape** \\ \end{tabular} } & \multirow{2}{*}{**Direction**} & \multicolumn{6}{c}{**Effective Mass**} \\ \cline{5-10}  & & & & **X-tra** & & **Y-tra** & & **Z-tra** & **X-rot** & **Y-rot** & **Z-rot** \\ \hline \multirow{2}{*}{1} & \multirow{2}{*}{0.181} & \multirow{2}{*}{Bend} & Along & \multirow{2}{*}{0.004} & \multirow{2}{*}{37,900} & \multirow{2}{*}{0} & \multirow{2}{*}{5,419,260} & \multirow{2}{*}{0.640} & \multirow{2}{*}{0} \\  & & & & & & & & & & \\ \multirow{2}{*}{2} & \multirow{2}{*}{0.181} & \multirow{2}{*}{Bend} & Along & \multirow{2}{*}{37,560} & \multirow{2}{*}{0.004} & \multirow{2}{*}{0} & \multirow{2}{*}{0.644} & \multirow{2}{*}{5,449,320} & \multirow{2}{*}{0} \\  & & & & & & & & & & \\ \multirow{2}{*}{3} & \multirow{2}{*}{0.253} & \multirow{2}{*}{Torsion} & \multirow{2}{*}{0} & \multirow{2}{*}{0} & \multirow{2}{*}{0} & \multirow{2}{*}{0} & \multirow{2}{*}{0} & \multirow{2}{*}{0} & \multirow{2}{*}{0.032} & \multirow{2}{*}{44,819} \\ \hline \hline \end{tabular} Note. “-tra” and “-rot” represent the translational component and the rotational component, respectively.  
\end{table}
Table 2: Vibration mode information and the effective mass of the filter capacitor.  
Figure 5: The first three mode shapes of the suspended filter capacitor.  
electrical equipment with the same voltage has a similar size and structure, so we can refer to the results in References [29; 44]. It can be found that the two 1 st mode frequencies of the simulation models are extremely close, which indicates the accuracy of the simulation model in this study.