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Selection of insulators

Jan 31, 2021

Selection of insulators


1 Characteristics of various insulators

Domestic overhead power transmission lines usually use the following three forms of insulators, namely porcelain disc insulators, tempered glass disc insulators, and rod composite insulators.

-Some countries such as Germany, Japan and the United States also use non-breakable structures and deep climbing skirts and rod-type porcelain insulators with medium and large climbing distances.

It has been used in some 500kV lines in my country. In addition, a new organic composite anti-pollution disc suspension insulator has been newly developed in China, which has been installed on 500kV lines.

Network operation.

1.1 Disc porcelain insulator

At present, porcelain insulators are still the most widely used insulators in power systems. High-strength porcelain for UHV insulators is made of quartz feldspar, clay and alumina.

Become. The inside of porcelain is a composite composed of crystalline phase, a small amount of pores and uneven glass phase. The physical and chemical properties of porcelain are mainly composed of the crystalline phase that constitutes its microstructure.

And the type and quantity of glass phase are determined. The particles are fine and fine, the bonding force between each other is strong, the porcelain medium formed is uniform, the mechanical strength is high, and the performance is stable. but,

The fineness of the noodles means that manufacturing techniques such as drying, forming and sintering are more difficult. Porcelain is a kind of brittle material, its compressive strength is much higher than tensile strength. As for the

To make electric porcelain have higher mechanical strength, the porcelain should be designed to withstand compressive stress as much as possible. The surface of porcelain pieces is usually covered with glaze to improve its mechanical strength.

The square water is soaked to increase the surface smoothness. In order to improve the pollution flashover resistance of porcelain insulators, an insulator covered with semiconductor glaze has also been developed. When the insulator surface leaks

When the current increases, the glaze heats up to evaporate the surface water, thereby preventing the generation and development of local arcs on the surface and preventing the occurrence of pollution flashover.

Disc-shaped porcelain insulators have good insulation properties, weather resistance, heat resistance and flexible assembly characteristics, and are widely used in various voltage lines. Disc porcelain

The color edge is a breakdown type. With the extension of running time, its insulation performance will gradually decrease, which is the so-called "aging" phenomenon of porcelain insulators.

This problem is more prominent when imperfect prevention, structural design is not optimized as much as possible, and production process control is not strict. At present, the average annual aging rate of domestic porcelain insulators is lower than

0.005%.

One of the major advantages of porcelain insulators is that when anti-fouling products are needed, they can be designed into a double umbrella or triple umbrella with a smooth surface under the umbrella tray.

Its aerodynamic characteristics are very conducive to self-cleaning under windy conditions, and the pollution rate is low, which effectively improves the anti-fouling ability, and is especially suitable for drought, less rain and sand

Many filthy fields.



1.2 Tempered glass insulator

The glass insulator has the same environmental stability as the porcelain insulator, the production process is simple, the mechanization is easy to realize, and the production efficiency is high. Main components of glass insulator

It is composed of acidic oxides such as SiO2, B2O3, Al2O3 and alkaline oxides such as Na2O and K2O. The raw materials are silica sand, feldspar, and boron including these components.

Sand, calcium carbonate, and many other natural raw materials and industrial medicines. Also add a small amount of auxiliary materials as clarifying agent and reducing agent. At temperatures above 1300°C

Annealing treatment is carried out after melt molding. The quench tempering makes the glass surface tempered. After annealing and tempering treatment, permanent compressive stress is formed on the glass surface, which resists

The formation and diffusion of micro-cracks on the surface significantly improve the mechanical strength of glass parts.

Toughened glass insulators have excellent electromechanical properties, high tensile strength, vibration fatigue resistance, thermal shock resistance, arc burn resistance, and electrical breakdown resistance. Still have

It has the characteristic of zero self-explosion, so there is no need for insulation test. Operation practice at home and abroad has proved that tempered glass insulators have long-term stable electromechanical performance.

That has a long service life.

The disadvantage of the tempered glass insulator is that due to the limitation of the manufacturing process, the anti-fouling type can only be made into a bell jar type. To improve the antifouling performance, the number of edges and height must be increased.

degree. As a result, the furrows are deep, easy to accumulate, difficult to clean, and poor self-cleaning performance. It is more suitable for coastal dirty areas with less dust and more weather. For less rainy areas,

It is not easy to be immersed in the wet, local area, which can hinder the development of leakage current and arc.

In addition, due to the spontaneous explosion characteristics of glass insulators, it has been reflected in pastoral projects that some herders regard glass insulators as objects for slinging stones for fun. This situation is

There is a similar statement in the United States. According to AEP engineers, some people like to shoot glass insulators. The company does not use glass insulators for its lines. Also due to

Glass insulators explode spontaneously, and their fragments scattered on the ground sometimes cause complaints from local residents.

1.3 Composite insulator

The main structure of composite insulators is generally composed of three parts: umbrella sheath, glass fiber reinforced plastic core rod and end fittings. Middle umbrella skirt jacket-generally made of high temperature vulcanized silicon rubber

Made of organic synthetic materials such as rubber and ethylene propylene rubber; FRP core rods are generally glass fiber reinforced plastic composite materials with glass fiber as reinforcement material and epoxy resin as matrix; end fittings

-Generally, it is carbon cast steel or carbon structural steel with a hot-dip galvanized layer on the outer surface. The mandrel and the umbrella skirt bear the mechanical and electrical loads respectively, thus integrating the umbrella skirt sheath

The material has the advantages of superior resistance to atmospheric aging and good tensile mechanical properties of the core rod material.

Composite insulator is a new type of anti-pollution insulator, which has the advantages of high strength, light weight, good pollution resistance, easy installation and small maintenance workload.

Composite insulators have 30 years of operating experience. After long-term development, the material formula has been continuously improved, the product design has been gradually improved, and the production art has become

mature. According to the survey report published by the Great Power Grid Conference in 2000, the damage rate of composite insulators was 0.035%.

The main problem currently existing in domestic composite insulators is the decrease in mechanical strength after operation. It should be shown as the mechanical strength test is removed after 2 to 3 years of operation.

During the inspection, it was found that some ends of the mandrel slipped or fell out of the end fittings under the rated mechanical load. This situation is at the end of various connection methods

It has happened in the head, especially the products using the outer wedge type, and even some foreign products that use the crimping type end. In addition, there are aging and hydrophobic

The impact of performance degradation, unexplained flashover, ice and snow on the safe operation of composite insulators and other issues. Especially in the wind and sand, strong ultraviolet rays, drought and less rain

In areas with severe weather conditions, the use of composite insulators should be carefully considered and further studied.



1.4 Long rod-shaped porcelain insulator

Long rod-shaped porcelain insulators have the advantages of invisibility, high mechanical strength, high reliability, long service life, good pollution resistance, easy installation and small maintenance workload.

.point.

Long rod-shaped porcelain insulators have more than 30 years of operating experience in more than 30 countries and regions, and the recorded annual damage rate is less than three parts per million.

Rod-shaped porcelain insulators began to enter my country in the late 1990s. The first trial was the Jiangsu and Anhui power grids in East China (598 strings for 500kV lines in Jiangsu, Anhui

198 strings for 110kV lines). At present, the rod-shaped porcelain insulators used in Jiangsu have a specific distance of 3.2cm/kV, and the specific distance used in Anhui is 2.5cm/kV, both of which are German

CERAM's products, in the I ~ grade pollution area, operating about 5,900, except for heavy cement pollution areas have achieved good results.

1.5 Organic composite pollution-resistant disc suspension insulator

Organic composite pollution-resistant disc suspension insulators absorb the advantages of porcelain insulators and composite insulators, maintain the stable and reliable mechanical strength of porcelain insulators, and have

The composite insulator has the characteristics of good pollution resistance and light weight. It has been connected to the network for 500kV line operation.


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