## 5 Pipeline Overvoltage Protection Based on Solid-State Decoupler
On the other hand, the induced electric potential of the pipeline insulation layer remains relatively stable and fluctuates within a certain range, which can be disregarded. The withstand electric potential of the insulation layer depends on the difference between the induced voltage of the pipeline insulation layer and the metal layer. Therefore, when the induced voltage of the insulation layer changes slightly and the induced electric potential of the metal layer continues to increase, the withstand voltage of the insulation layer gradually decreases. When the bare copper wire length (\(pl_{1}\)) is 0 m, the induced voltage amplitude of the metal layer of the natural gas pipeline is 42.25 kV and the voltage amplitude of the insulating layer is 7.23 kV. When the bare copper wire length is 80 m, the induced voltage amplitude of the metal layer of the natural gas pipeline is 43.43 kV and the voltage amplitude of the insulating layer is 5.45 kV. Similarly, when the bare copper wire length is 200 m, the induced voltage amplitude of the metal layer of the natural gas pipeline is 43.59 kV and the voltage amplitude of the insulating layer is 5.39 kV. It can be observed that increasing the length of the bare copper wire from 0 m to 80 m results in a decrease in the withstand voltage of the pipeline insulation layer from 7.23 kV to 5.45 kV, representing a decrease of 24.62%. However, when the length increases from 80 m to 200 m, the withstand voltage of the pipeline insulation layer decreases only slightly from 5.45 kV to 5.39 kV, representing a decrease of 1.10%. To better understand the impact of the external bare copper wire of the solid-state decoupling device on the overvoltage of the natural gas pipeline, in close proximity, we focused our research on the central section of the tower grounding grid. This section, which is perpendicular to the natural gas pipeline, was chosen as the research path. Figure 16 illustrates this selection, with a research path length (\(l_{\rm r}\)) of 400 m and depth (\(\hbar_{3}\)) = 2 m. By conducting simulation calculations, we obtained the soil potential change curve for the path under different lengths of the bare copper wire (\(pl_{1}\)), as depicted in Figure 17.  
Figure 17 demonstrates that the implementation of solid-state decoupling primarily alters the soil potential surrounding the bare copper wire and the pipeline location. However, it has minimal impact on the soil potential of the tower grounding grid and other regions. As the length of the bare copper wire increases, the soil potential around it gradually decreases. Conversely, the soil potential at the pipeline position exhibits a gradual increase. Figure 16: Research path top view. The subsequent increase of 120 m of bare copper wire has minimal impact on reducing the voltage of the pipeline insulation layer. Therefore, increasing the length of the bare copper wire does not improve the overvoltage protection effect of the pipeline. In practical engineering, it is more economical and convenient to determine the length of the bare copper wire according to Figure 14b. The detailed calculation term equation is shown in term Equation (5).