Insulator flashing and flashing

A device that insulates a live part and mechanically supports it is called an insulator. In particular, insulators that operate outdoors should have a certain electrical insulation performance and mechanical strength of a certain strength, and should also have the conditions to withstand the invasion and pollution of various natural environments to ensure safe power supply. According to the use, it can be divided into three categories: line insulators, substation support insulators and casings. According to the material of the insulator. There are currently porcelain, glass and organic composite insulators.

There are many types of insulators that fail during operation. At present, the impact on the power system is relatively large, and the more frequent accidents are the pollution flashover accidents of the porcelain insulators of the power transmission and transformation equipment under the operating voltage. The lightning flash accident of the outdoor high voltage bushing and insulator of the substation and the "zero value" of the line suspension insulator caused the landing of the high voltage wire. This chapter focuses on the analysis of the first two accidents, and makes reference to its fault detection method and operation and maintenance.

Insulator discharge

Insulation pollution discharge is often referred to as the external insulation flashover of the power transmission and transformation equipment under the working voltage. This flashover is not due to an increase in the applied voltage. It is the result of a decrease in the insulation capacity of the insulator surface. It has a unique discharge mechanism. It is related to factors such as insulation surface area contamination, surface soil layer wetting, and the resistance characteristics of the insulator itself. In order to correctly analyze the cause and take effective preventive measures, this section will introduce in more detail the process of insulator fouling discharge, the mechanism and the pollution resistance characteristics of various insulators and their influencing factors.

Insulator overview and hazard

With the development of industry, the increase of power grid capacity and the increase of rated voltage level, the pollution flashover accident of the external insulation of power transmission and transformation equipment has become increasingly prominent. According to incomplete statistics, there were 1126 pollution flashovers in China's transmission lines from 1971 to 1980, and 761 accidents in substation equipment. By 1981-1990, the number of pollution flashovers on transmission lines reached 1907. There were 695 accidents in substation equipment, and the number of pollution flash accidents in the last ten years was generally higher than in the previous decade. The accident is not only manifested in the increase in the number of times, but also in the expansion of the area and its severity. Table 10-1 lists the major pollution flashovers that have occurred in China since the 1970s. It can be seen from Table 10--1 that the pollution of China's power system has occurred in the 1950s and 1960s and is concentrated in the relatively developed industries. Regional accidents occurred one after another; in the late 1980s and 1990s, cross-regions Large-scale pollution flashes across provinces and cities have also begun to appear. The losses to the national economy are getting bigger and bigger.

Pollution flash is a regional issue. Its remarkable feature is the high probability of simultaneous multi-point tripping. The lower the insulation, the larger the trip rate and the smaller the recombination power. According to statistics from North China Power Grid from 1975 to 1985, the transmission line trip rate was 27%. From 1996 to 1997, several times, the coincidence of the substation equipment of Beijing, Tianjin and Tang power grids failed. Poor coincidence means that there is a permanent failure, and multiple failures mean that multiple power supplies lose power, and even cause large-scale accidents.

The above characteristics of the flashover are caused by its own particularity. A large and medium-sized substation, the number of insulation equipment to the ground is about a few hundred to thousands; and the substation has several to a dozen lines of incoming and outgoing lines, in areas around tens or hundreds of square kilometers. Atmospheric pollution is almost similar, and the wet weather conditions such as fog, snow, and drizzle are almost the same. Once a flashover trip occurs, it indicates that nearly a few hundred or thousands of insulators in the same area are in a critical flashover state. When a trip occurs, the reclosing action will also cause the oscillation of the power grid, so that the adjacent flashover device is subjected to an operation overvoltage, which makes the device in a more unfavorable state. Especially when the insulation resistance of the external insulation of many equipments is much lower than the actual pollution degree, it will often cause a large-area pollution flashover in the region. From the end of 1989 to the beginning of 1990, the fundamental reason for the large area of ​​several provinces and cities nationwide was the level of external insulation of the transmission line configuration, which was far from the actual level of contamination on the surface of the equipment.