## 3 Cable Terminal-Sheath Structure Electric Field Simulation Research
When the outer surface is uniformly wet, the equipotential line inside the first umbrella skirt is almost parallel to the axial direction, and the potential decreases from the upper surface of the umbrella skirt to the lower surface of the umbrella skirt. The reason for this phenomenon is that when there is no pollution, the potential distribution of the cable terminal structure is mainly determined by the equivalent capacitance. Because the cable core has the highest potential, the farther away the measurement point is from the cable core, the lower the potential. Therefore, when  
Figure 4: Equipotential line diagram with a clean outer surface of the cable terminal. Figure 5: Equipotential line diagram when the outer surface of the terminal is covered by evenly distributed wet dirt. there is no pollution, the potential distribution inside the first umbrella skirt is distributed along a radial direction. When there is uniform pollution on the outer surface of the cable terminal, the electric field distribution outside the cable terminal is mainly determined by the wet pollution resistance. Since the highest potential on the outer surface can be found in the upper fittings and cable core, the farther away they are from the upper fittings and cable core, the lower the potential. In addition, at the top of the first umbrella skirt, due to its small radius of curvature, the potential line is relatively dense in uniform wet pollution, so the electric field here is very high. Electric Field Distribution of a Cable Termination-Sheath Structure Without External Moisture Contamination  
2.1 No Air Gaps Are Present Between Cable Terminals and Jackets, with No Interfacial Moisture Contamination  
The inner surface of a well-installed insulating sheath structure should fit well with the umbrella skirt column and metal flange of the cable terminal, and there should be no wet dirt and air gap defects on its interface. Here, the electric field was simulated when an insulating sheath was installed on the upper and lower fittings of the cable terminal. Figure 6 shows the electric field cloud diagram when the outer surface of the cable terminal sheath structure is free of dirt, and Figure 7 shows the distribution diagram of the electric field along the surface with and without a sheath, respectively. It can be seen that under the conditions of no pollution on the outer surface, the electric field distribution of the cable terminal after installing the sheath is basically not very different from that without the sheath, and the voltage distributed on the sheath is very small. With the insulating sheath, the leakage current mainly flows through the lower flange through the insulating sheath. At this point, the leakage current is mainly a capacitive current, and at this time, the presence or absence of the sheath will not affect the electric field on the surface of the cable terminal. We installed a uniform pollution layer on the outer surface of the cable terminal-sheath structure, with the size of the pollution layer the same as that in Section 2.1, to analyze the potential and electric field under wet pollution conditions after installing the insulating sheath. As shown in Figures 8 and 9, the potential diagram and electric field diagram along the outer surface of the pollution layer when the outer surface of the cable terminal sheath structure is uniformly wet. It can be seen that after the installation of the insulating sheath, due to the increase in surface leakage distance, the decline of surface potential slows down, and the electric field of the wet polluted surface decreases as a whole. Among the fields, the electric field at the top of the first umbrella skirt decreases the most, and the electric field at the root of each umbrella skirt decreases. This shows that the existence of a sheath can indeed reduce the probability of surface flash  
Figure 6: Electric field cloud diagram with a clean outer surface on the sheathed terminal.