## 5 Pipeline Overvoltage Protection Based on Solid-State Decoupler  
The solid-state decoupler is a product designed to protect against AC/DC interference. It combines embedded current drainage, surge protection, and AC decoupling, and has a high capacity for breaking impact currents. Internally, it typically consists of capacitors, thyristors (or diodes), and surge protection devices connected in parallel. Figure 13 illustrates the appearance and internal circuitry of the solid-state decoupler, while Table 3 provides its technical parameters. This section aims to decrease the electric potential of the pipeline insulation layer by utilizing the specific wiring method of the solid-state decoupler. It also seeks to validate  
Figure 13: Solid-state decoupler. (**a**) Physical images. (**b**) Circuit diagram in thyristor mode. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline DC Leakage/mA & \(\leq\)1 mA & Isolation Voltage/V & +2/ –  
the solid-state decoupler's ability to reduce the voltage of the pipeline insulation layer through modeling and simulation. Figure 13(a) illustrates the simulation diagram. In this setup, a bare copper wire is placed parallel to the natural gas pipeline, with a distance of 1m between them. The length of the bare copper wire is determined based on the current dispersion characteristics of the tower grounding grid. In order to save cost and avoid excessive design, the laying length of bare copper wire \(pl_{1}\) is defined as shown in Figure 13(b). The calculation term equation of laying length of bare copper wire is shown in term Equation (1). In this section, \(pl_{1}=0\) m indicates that there are no protective measures for natural gas pipelines. \[pl_{1}=2\times\left(d_{gp1}-0.5\times l_{ga}\right)+l_{ga} \tag{5}\]  
In term Equation (5), \(pl_{1}\) is the length of bare copper wire laying, \(d_{gp1}\) is the \"tube-line\" spacing, and \(l_{ga}\) is the length of the epitaxial ray. To evaluate the effectiveness of the method, a simulation model is created using COMSOL Multiphysics simulation software, as illustrated in Figure 13(a). The aim is to analyze the impact of varying laying lengths of bare copper wire (\(pl_{1}\)) on the resistive coupling overvoltage of natural gas pipelines at the cross-crossing. The simulation parameters used are as follows: lightning peak current (I\({}_{0}\)) = 50 kA, soil resistivity (\(\rho\)) = 1000 \(\Omega\)-m, spacing between the tube and the line (\(d_{gp1}\)) = 40 m, length of the epitaxial ray (\(l_{g1}=l_{g2}\) = 20 m), commutation angle (\(\alpha\)) = 45\({}^{\circ}\), and cross angle between the tube and the line (\(\beta\)) = 0\({}^{\circ}\). The laying lengths of bare copper wire considered are \(pl_{1}\) = 0 m, 30 m, 40 m, 50 m, 80 m, and 200 m. Figure 15 depicts the overvoltage amplitude of natural gas pipelines under different lengths of bare copper wire, as determined through simulation calculations. Figure 14: Solid-state decoupler wiring diagram. (**a**) Simulation diagram. (**b**) Bare copper wire length diagram. Figure 15: Influence of bare copper wire length on overvoltage of natural gas pipeline. (**a**) Induced voltage amplitude of metal layer and insulation layer of pipeline. (**b**) Voltage amplitude of pipeline insulation layer. According to the results shown in Figure 15, as the length of the bare copper wire increases, the induced voltage of the metal layer of the natural gas pipeline also increases gradually, while the voltage of the pipeline insulation layer decreases gradually. This phenomenon occurs because the solid-state decoupler causes an instantaneous short-circuit between the bare copper wire and the pipeline when subjected to lightning impulse current. The soil potential in the area where the bare copper wire is located is much higher than the induced voltage of the pipeline metal layer, leading to an increase in the induced voltage of the pipeline metal layer during the short-circuiting process.