1. Analysis of electrical and environmental stress of composite insulators in operation
Under the combined action of electrical and environmental stress, surface dry belt arc can cause corrosion or marking of materials, water, electrical corrosion, chemical pollution of environmental factors can cause electrical damage of silicone rubber materials. The hydrophobicity loss of composite insulators in operation is mainly caused by electrical aging and manufacturing defects. The specific analysis is as follows:
(1) The wind blows through the composite insulator string to form eddy currents, and heavy dust and other dirty materials fall on the surface of the insulator. Under the combined action of ultraviolet light and mechanical force, the surface is slightly corroded, the surface roughness increases, and the invisible fine cracks are formed. The dirty layer is attached to the surface.
(2) The continuously diffused low molecular polymer migrates the surface of the umbrella and implanted into the dirty layer, so that the dirty material is covered with a very thin silicone and oxygen molecular polymer, and the surface maintains hydrophobicity.
(3) In bad weather, such as fog, dew, high humidity and light rain, small water droplets can form on the insulator surface. However, in places with serious surface erosion, small water droplets combine with the wet deposition of dust to form sewage droplets, which pass through the thin silico-oxygen polymer layer to form a conductive layer and promote the leakage current to change from capacitance to resistance.
(4) Due to the uneven distribution and wetting of the dirty layer, local multi-point high voltage parts are generated on the insulator surface, and thus point-like discharge occurs.
(5) the discharge consumes the thin layer of polymer around the small water drop and damages the hydrophobicity of the silicone rubber.
(6) The damage of hydrophobicity of the surface causes the water bead to form a water film. A continuous conductive layer is formed, which further increases the leakage current.
(7) The heat generated by the leakage current forms a local dry area on the surface. The surface is a conductive surface with high resistivity and a hydrophobic surface containing water beads, so the voltage distribution is uniform.
(8) Uneven voltage distribution is formed in different drying zones, so arc discharge will be generated and the surface will further lose hydrophobicity. The drying zone will be further extended. Discharge and partial arc will cause serious erosion of the insulator surface, resulting in the aging of the skirt surface.
(9) In a long dry period without discharge of the insulator, the silicone rubber will recover its hydrophobicity, and the self-recovery time generally needs 6-8 hours.
(10) If further discharge on the insulator surface accelerates the aging of silicone rubber, local high temperature will be generated. In severe cases, the heating temperature is between 260-400℃, while the highest temperature tolerated by silicone rubber materials is only 300-400℃. Therefore, white powdery substances will occur on the surface of insulators with frequent discharge, which is a new chemical reaction at high temperature. Cyclic discharge eventually causes permanent deterioration of insulator surface and permanent loss of hydrophobicity, resulting in loss of excellent pollution resistance of composite insulators.
2. Hydrophobicity loss caused by accelerated aging caused by manufacturing of composite insulators
The control of pollution flashover in the manufacturing process of composite insulators mainly consists of hydrophobicity and corrosion resistance. Hydrophobicity and hydrophobic self-recovery is the first close of antifouling flashover, good hydrophobicity, will make the pollution layer resistance is high, leakage current is small, pollution lightning pressure can be improved. After hydrophobicity loss and temporary loss, the umbrella skirt coat should be able to withstand the dry belt arc no trace, no erosion, which is the second key to anti-fouling flashover. The shape and design size of sheath skirt will affect the hydrophobic performance and leakage current. The scientific and reasonable design of shape and size is the third key to anti-fouling flashover.