The earliest silicon-based composite insulators have been used for more than 40 years. Considering their spiral use and years of use, research into in-service defect or damage monitoring methods has become important. There are a number of potential failure modes that represent potential threats to the full operation of composite insulators, including flashover, aging, and mechanical failure.
In the first category, lightning flashover is usually a common threat to these insulators, mainly because it depends on the dry arc distance and has little to do with the insulator material. If the dry arc distance of a composite insulator is the same as that of a porcelain or glass string, its flashover withstand capability is basically the same. Although composite insulators cannot increase the lightning flashover voltage, they cannot reduce the lightning performance of the line. Regardless, auto-reclosing is usually successful in this situation, so the impact of this potential problem on network reliability is relatively low.
Because the silicone rubber shell has excellent hydrophobicity and hydrophobic transmission properties, composite insulators have excellent pollution performance. This translates into relatively few contamination flashovers, which is one of the main reasons for its widespread use. Flashovers caused by bird droppings, on the other hand, present a much bigger problem, primarily because large birds release "streamers" near the top of the insulator, i.e., essentially portions of the conductor that "float in the air." , thus greatly distorting the electric field D of the insulator. distribute. Additionally, if the streamer is close to the edge of the insulator, the distortion in the electric field is greater and flashover is more likely to occur. Composite insulators are more susceptible to flashover from bird streamers than porcelain or glass strings because of their smaller shed diameter. In fact, the majority of flashover failures recorded as unexplained were probably triggered by birds.
The second largest threat to composite insulators is aging, which involves the occurrence of surface phenomena such as cracking or cracking due to natural weathering. The aging of silicone rubber is often accompanied by a decrease in hydrophobicity and a corresponding decrease in pollution flashover resistance. However, aging can also be caused by other factors, such as pecking birds that can damage a silicone shed, or sustained strong winds that can tear a shed apart depending on its diameter and design. Mechanical failure is the third major type of problem that can arise, primarily involving the core of a composite insulator breaking, causing the conductor to fall off.
Basically, operational monitoring of composite insulators consists of inspections to determine the type and extent of damage associated with these possible failure modes. In the event of a lightning flashover, a lightning location system is usually provided which can assist maintenance personnel in locating the affected tower. In our country, the policy of power supply companies is to determine which composite insulators have experienced lightning flashover and replace them to eliminate potential damage risks. Online leakage current monitoring is often used to evaluate its resistance to pollution flashover. For flashovers caused by bird streamers, inspections are used to look for nests on towers or the presence of large birds nearby. Likewise, when it comes to aging and damage to silicone sheds, visual inspection is the primary technique-with or without the aid of optical equipment.
