## 2 Structural Parameters and Simulation Model  
### Physical Structures and Structural Parameters  
The analyzed filter capacitor functions in an \(\pm\)800 kV ultra-high-voltage (UHV) direct current power transmission system. The transmission grid system comprises a series of converter stations, serving as nodes, interconnected by a number of transmission lines. In an \(\pm\)800 kV converter station, a suite of equipment interconnected by conductors or wires constitutes the whole substation system. In the station, two identical suspended filter capacitors are in operation, one of which is the focus in this paper. The filter capacitor is a suspended structure that is installed on a door-like steel gantry. The materials of the gantry adopt Q345 steel. The overall structure and sizes are depicted in Figure 2. The overall structure mainly consists of the steel gantry, the filter capacitor, the interlayer glass-fiber reinforced polymer (GFRP) insulators, and the top and the bottom tension insulators. The steel gantry is a single-span lattice frame with a span of 24 m. The total height of the steel gantry is 45 m, and the height of the suspension point of the filter capacitor is 42.5 m. The components of the beam and columns of the steel gantry are provided in Table 1, including the cross-section information and sizes. The filter capacitor is fixed to the gantry by the top tension insulators and to the ground by the bottom tension insulators. The top insulators have a length of 10.560 m while the bottom insulators have a height of 4.053 m.  
The filter capacitor has a total of 32 layers arranged in two rows per layer. Each layer has eight capacitor modules, organized in double rows, with four modules per row, as shown in Figure 2b. Each layer, accounting for the grading ring and other attachments, has a mass ranging from 1000 to 1500 kg. The upper layer has a mass of 1500 kg, whilst the lower layer has a mass of 1400 kg. The layers of the filter capacitor are interconnected by four vertically suspended GFRP insulators with hinge joints, so such a suspension structure with hinge connections has an obvious geometric nonlinearity. Figure 2c shows the details of the top suspended insulators. They are connected to the gantry and the top layer of the capacitor with hinge joints. The four top insulators and the interlayered insulators are perpendicular to the ground and separated by 2.40 m and 2.07 m along the two horizontal orientations. With an inclined degree of 63, the bottom tension insulators are installed as the  
Figure 2: Structures and sizes of the \(\pm\)800 kV suspended filter capacitor.  
connection of the filter capacitor and the ground. The two ends of the inclined insulators are both hinge joints.  
All insulators in the suspended filter are made of GFRP composite materials whose specified tension load (STL) is 300 kN and elastic modulus is 60 GPa. The lengths of the top insulators and the bottom insulators are 10.50 m and 4.05 m, respectively. The height between the capacitor layers is 0.85 m. The diameters of the top and bottom insulators are 30 mm whereas the diameter of the interlayer insulators is 45 mm. For reducing the dynamic response of the filter capacitor, a pre-tension force is applied to the bottom insulators. As shown in Figure 2d, there is a regulating instrument on each bottom insulator so that the pre-tension forces of the four insulators can be adjusted artificially. The pre-tension force of the bottom insulators of the suspended filter capacitor is set to 20 kN during the initial design to reduce the oscillation and seismic responses.