Station post insulators are used for insulation and mechanical fixed connection between conductors and grounding bodies, such as post insulators for busbars or isolation switches. It is composed of solid porcelain columns and upper and lower metal accessories assembled by cement. The flashover distance of the post insulator along the external air is almost the same as the internal penetration path, so only the external flashover will occur, and the breakdown of the internal ceramic dielectric will not occur. It is a non-breakdown type. When the voltage level is higher, several post insulators can be connected in series. The post glass insulators will bear the action of bending moment and torque. In order to improve the mechanical strength, sometimes several sets of post insulators are connected in parallel.
In recent years, a composite station post insulator with a porcelain post as a core rod and a silicone rubber material as a sheath has been developed. The insulator uses a porcelain rod to withstand mechanical force, because cylindrical porcelain rods are easier to fire than those with umbrella groups. The strength is higher, and the pollution flashover resistance of the silicone rubber material is much higher than that of the porcelain material. Therefore, the electrical and mechanical properties of the insulator are better than those of the electric porcelain power station post insulator, and it has a broad development prospect.
The composite insulator can indeed be replaced if one of the following situations occurs.
1. The umbrella cover is brittle and internalized, powdered or cracked.
2. Umbrella cover re-repair is prone to traces and corrosion due to leakage, and the cumulative length is greater than 10% of the insulator's creepage distance, or the corrosion depth is greater than 30% of the material thickness at the location.
3. The sealing failure of each link part of the composite insulator, cracks and slippage appear.
4. The insulator is burned by arc on the surface of the umbrella skirt after the flashover.