Under normal power frequency voltage, especially in high temperature and humidity weather or polluted HTV silicone rubber composite insulator may operate under flashover, and the discharge mechanism of hydrophobic composite insulator is different from that of porcelain and glass insulator. When the same creepage distance and hydrophobicity are good, the effective creepage distance of composite insulator is larger than that of porcelain insulator and glass insulator. When the hydrophobicity of composite insulator drops above HC5, its effective creepage distance can be smaller than that of porcelain and glass insulators. The HTV silicone rubber umbrella has deteriorated and the flashover of composite insulator has been operated for several years.

The hydrophobicity of HTV silicone rubber can reduce the humidity of composite insulators by 10% and 30%, and the operating frequency pollution withstand voltage reduces by 30%~40% The obvious decrease of power frequency intensity is also one of the reasons for flashover. If the hydrophobic part or total loss, the disc diameter and umbrella distance are small, it is easy to have a short arc canopy under high humidity atmospheric conditions, and reduce the electrical strength. This is one of the main reasons for composite insulator flashover, which should be paid enough attention to by the production enterprises and operation departments.

The 220 kV line does not have a high pressure balance device installed at the end of the composite insulator. When the voltage equalizing device is installed or the voltage equalizing device at the high and low voltage sides is installed separately, the umbrella skirt of the potential distribution at the high voltage side accounts for 17.2%, 12.4% and 10.1% of the operating voltage respectively. The installation of the balance device greatly reduces the voltage at the attachment connection point at the high voltage side, and greatly improves its power frequency electrical performance.

Install circular rear balance devices with protective layer thickness of 40mm and 75mm respectively, the second umbrella skirt of the potential distribution of 21.3% and 12.2% of the operating voltage at the high voltage side, and the depth of the potential distribution curve of 75mm are more uniform than the potential distribution curve of the insulator with insulator coverage depth of 40mm, and the depth of coverage on the impact potential distribution equalization device is larger. When the equalizing device is installed, the high voltage of the potential distribution on the insulator accounts for 19% of the operating voltage, 1.8% higher than that of the insulator without the equalizing device, indicating that the correct installation of the equalizing device has a great impact on the electrical performance of the composite insulator.

The skirt shape is optimized according to the pneumatic principle and external insulation. The umbrella is a porcelain and glass insulator with the diameter of 200-250mm and the spacing of 130-150mm, which improves the effective creepage distance of the unit umbrella and greatly reduces the power frequency flashover voltage of the silicone rubber insulator under the high humidity environment during normal operation, that is, under the high humidity environment, the hydrophobicity of the hydrophobic composite insulator drops to a level. It is equivalent to the operation of XP 160 disc suspension porcelain and glass insulator.