Replacing the original porcelain insulators or glass insulators with composite insulators is one of the important technical measures to prevent pollution flashover. Under the same creepage distance and pollution conditions, the anti-pollution flashover ability of composite insulators is significantly higher than that of porcelain insulators and glass insulators. The reasons are as follows.
(1) The surface of the silicone rubber umbrella skirt is a low-energy surface with good hydrophobicity and ability to migrate, making the dirt layer also hydrophobic. The water on the dirt layer surface appears in the form of small water droplets, which makes it difficult to form a continuous water film. Under the action of continuous voltage, it does not form a concentrated and strong arc like porcelain and glass insulators, and it is not easy to form a concentrated discharge channel on the surface, so it has a higher pollution flashover voltage.
(2) The diameter of the composite insulator is small, and the surface resistance is larger than that of porcelain and glass insulators under the same pollution conditions, and the pollution flashover voltage is correspondingly higher.
(3) Unlike the umbrella rib structure on the lower surface of porcelain and glass insulators, the structure and shape of the umbrella skirt of composite insulators is not conducive to the adsorption and accumulation of dirt, and does not require cleaning of dirt, which is beneficial to the operation and maintenance of the line.
In addition to excellent anti-pollution properties, composite insulators have high mechanical strength, small size, light weight, easy operation and maintenance, and high economy. The composite insulator is a non-breakdown structure, and there is no zero detection problem.
However, with the rapid increase in the amount of composite insulators used, the cases of flashover and damage are also increasing. The main causes of on-site damage of composite insulators include: mechanical damage, mainly including brittle fracture, typhoon and other factors causing the core rod to break. This type of accident has serious consequences and may lead to malignant accidents in the power grid; electrical damage to insulators, such as flashover and internal breakdown.
The damage of composite insulators mostly occurred in early products, mainly including improper material selection and immature technology. China's annual damage rate of composite insulators is about 0.005‰, which is better than the average level of other countries in the world. However, it needs to be pointed out that composite insulators will also have pollution flashover failures due to the following reasons: rapid or excessive dirt accumulation on the surface makes it difficult for the hydrophobicity to migrate; external factors such as climate and environment cause the insulator to weaken or temporarily lose the hydrophobicity; and the aging of silicone rubber materials will cause decline of hydrophobicity and pollution flashover performance.