1. Material properties toughened glass strength and steel, high thermal stability, than porcelain is not easy to aging and long life. The difficulty of composite insulators is to solve the aging of organic materials under outdoor conditions, brittle break and creep of mandrel. It can be seen that tempered glass not only has much higher mechanical and insulating strength than porcelain, but also has excellent anti-aging properties than organic materials, which lays a good foundation for the reliable operation of insulators.
2. Product structure and pollution resistance
Glass insulator adopts cylindrical head structure, bearing components under uniform force, has the characteristics of small size, light weight, high strength and excellent electrical performance. Because the linear expansion coefficient of glass is much larger than that of porcelain, the appearance size is much smaller than that of composite insulating materials, and it is easy to connect with metal accessories and cement, so the material of stress components is well matched. Under various climatic conditions, it is not as easy as porcelain and composite insulators to produce dangerous stresses and lead to aging. It is difficult for composite insulators to solve the structural quality of composite interface. However, composite insulators have excellent pollution resistance and usually do not require cleaning. This greatly reduces line maintenance costs. Glass insulators have large leakage distance, less condensation on the surface and strong resistance to thermal stress caused by pollution, so they are not prone to flashover accidents.
3. Mechanical Properties
The strength of mechanical and electrical failure load is an important index of insulator performance. It is found that the mechanical strength of insulators with poor test results decreases gradually with the increase of running time. After 15-20 years of operation, the test value of some porcelain insulators is lower than the factory test standard value, and the unqualified rate increases with the extension of operation years. After high frequency vibration fatigue test, the mechanical and electrical strength of porcelain insulator decreases obviously. The stability and dispersibility of glass insulators are better than those of porcelain insulators, and the mechanical and electrical strength of glass insulators does not change much after high-frequency vibration fatigue test. The mechanical and electrical failure resistance strength of composite insulators is relatively high, but after several years of operation, the mechanical strength of composite insulators is removed for mechanical strength test, and it is found that the mechanical strength of composite insulators also decreases to a certain extent.
4. Lightning flashover performance
Lightning flashover occurs on insulators in the following two situations: Counterattack: If lightning strikes the tower or lightning rod directly, it will cause overvoltage on the insulation of the line. Once this instantaneous high voltage exceeds the shock discharge voltage of the insulator string, the insulator will flashover. Winding strike: Although there is a grounded lightning rod above the overhead power line, the lightning sometimes bypassing it and directly impacts the wire, namely winding strike. When winding strike occurs, the lightning will generate hundreds of thousands of volts of lightning overvoltage on the line. If the overvoltage exceeds the impact flashover voltage of the insulator string of the line, namely, the insulator string will flashover and cause the line to trip. According to operational experience, the lightning flashover failure rate of composite insulators is higher than that of porcelain glass insulators in transmission lines, especially in the transmission lines with the voltage level of 110kV and below. Lightning flashover of insulators will cause tripping of transmission lines, which is very unfavorable to transmission and power supply. Therefore, we should try to improve the lightning resistance level of transmission lines. The main lightning protection measures are: set up lightning arrester to reduce the grounding resistance of the tower; Erection of coupling ground wire; Adopt unbalanced insulation; Use arc suppression coil grounding: use line arrester: strengthen insulation and so on.
5. Deterioration performance
For the selection of transmission line insulators, the deterioration of insulators must be considered. According to current operational experience, the deterioration of porcelain insulators is manifested as "zero value" and "low value" of head stealth. For porcelain insulators with zero or low value, it is necessary to test them on the pole one by one, which requires a lot of manpower and material resources every year. Moreover, the accuracy of testing is greatly affected by the experience of operators, atmospheric humidity, manual adjustment of spark gap distance and other factors. On the other hand, the deterioration rate of porcelain insulators belongs to late exposure. Under the action of mechanical and electrical load, the deterioration rate will gradually increase with the increase of running time. Glass insulators have the characteristics of zero value self-detonation, and the self-detonation rate of glass insulators operating in areas with serious pollution will increase. The self-detonation rate of glass insulators belongs to early exposure, and with the increase of operation time, the self-detonation rate is decreasing year by year. As long as periodic inspection is carried out, defective glass insulators can be found and replaced in time without the need of tower climbing. The operational reliability of composite insulators is better than that of porcelain and glass insulators, but with the increase of operating time, the deterioration of organic materials will gradually become prominent.
6. Anti-aging rate
With the increase of operating life, different types of insulators have aging problems to some extent. The anti-aging ability of porcelain insulators is strong, but the aging becomes more and more serious with the increase of running time. The electrical strength of glass insulation generally remains the same throughout the operation, and its aging process is relatively slow; Synthetic insulators are made of organic materials that age much faster than inorganic materials such as porcelain and glass. The aging of insulators will lead to the deterioration of their performance in many aspects. Therefore, the aging problem should be considered in the selection and maintenance of insulators.