The Technology and Characteristics of Aging Detection for Composite Insulators

With the improvement of composite insulator technology, the number of composite insulators has rapidly increased, most of which are made of silicone rubber as the sheath material. The main reason for choosing composite insulators abroad is their light weight and low cost. In China, the composite insulators currently in operation are all silicone rubber insulators, mainly aimed at solving the pollution flashover problem, which is closely related to the characteristics of overhead lines in China. Compared with traditional porcelain or glass insulators, composite insulators have advantages such as high strength, light weight, strong wet flashover resistance, high lightning voltage, and simple operation and maintenance.
The external insulation of composite insulators adopts organic silicone rubber, and the aging resistance of organic materials is far inferior to that of inorganic ceramics or glass. During operation, the umbrella and sheath materials of composite insulators generally exhibit different aging phenomena, such as leakage marks or electrical corrosion, cracking, cracking, breakdown, pulverization, fading, brittleness, and hardness. The severe aging of external insulation materials is the main reason for the elimination or replacement of many early operating composite insulators.
The commonly used electrical method for diagnosing the aging of composite insulators is to measure their flashover voltage in fog. It is reported that the changes in the electrical performance of composite insulators before and after aging can be evaluated by measuring the flashover voltage of composite insulators in fog (clean fog or salt fog).
In laboratory and on-site research, leakage current is considered one of the important parameters for detecting the aging status of insulators. The leakage current waveform can provide useful information, and the harmonic component of the waveform can serve as a sign of whether insulators need to be cleaned.
The above two insulation aging evaluation methods were studied from a macro perspective. However, during the aging process of insulation materials, the microstructure of the insulation material will change. Therefore, it is necessary to analyze the aging mechanism of insulation materials from a microscopic perspective and find evaluation methods for insulation aging.
The main factors causing the aging of composite insulators include surface discharge (corona discharge, arc discharge), ultraviolet radiation, temperature, and pollution. Among them, surface discharge has a serious impact on the performance of composite insulators. When the field strength on the surface of the insulator reaches 0.5-0.7kV/cm, corona discharge will occur between the water droplets on the insulator surface. Surface discharge is the main cause of aging of composite insulators, including arc discharge and corona discharge. The mechanism of dielectric degradation damage caused by partial discharge is roughly as follows:
(1) The impact of charged particles generated by partial discharge on the surface of silicone rubber causes the main chain of silicone rubber molecules to break, and the polymer depolymerizes or partially turns into low molecules;
(2) The manufacturer of post insulators believes that partial discharge causes a local temperature increase on the surface of the insulator, and the high temperature in the discharge area can cause chemical decomposition of silicone rubber materials;
(3) The oxidation and corrosion of active gases O3, NO, and NO2 generated by partial discharge gradually deteriorate the silicone rubber material; (4) The ultraviolet radiation or long wavelength X-ray generated by partial discharge leads to the depolymerization and decomposition of silicone rubber.