Insulators are devices that are installed between conductors of different potentials or between conductors and ground elements and can withstand voltage and mechanical stress. There are many types and shapes of insulators.

Although the structure and shape of different types of insulators are quite different, they are all composed of two parts: insulating parts and connecting fittings.

Insulator is a special insulation control, which can play an important role in overhead transmission lines. In the early years, insulators were mostly used for telegraph poles, and gradually developed into a high voltage wire connecting tower with a lot of disk-shaped insulators hanging at one end. It is to increase the creepage distance, usually made of glass or ceramic, called insulators.

Insulators can be divided into suspension insulators and pillar insulators according to different installation methods. According to the different insulating materials used, it can be divided into porcelain insulator, glass insulator and composite insulator (also known as composite insulator); According to the different voltage levels, it can be divided into low voltage insulators and high voltage insulators; According to the different environmental conditions, the pollution resistant insulators used in polluted areas are derived. According to the different types of voltage, DC insulators are derived; There are also a variety of special purpose insulators, such as insulation crossbar, semiconductor glaze insulator and tension insulator for power distribution, spool insulator and wiring insulator.

In addition, according to the breakdown possibility of insulating parts, it can be divided into type A non-breakdown insulator and type B breakdown insulator.

Suspension type insulator
Widely used in high voltage overhead transmission lines and power generation, substation soft bus insulation and mechanical fixation. In the suspension insulator, it can be divided into disc suspension insulator and rod suspension insulator. The disc suspension insulator is the most widely used type of insulator in transmission lines. Rod suspension insulators have been widely used in Germany and other countries.

Pillar insulator
It is mainly used for insulation and mechanical fixation of bus and electrical equipment in power plants and substations. In addition, pillar insulators are often used as components of electrical equipment such as isolators and circuit breakers. In the pillar insulator, it can be divided into pin type pillar insulator and rod type pillar insulator. Pin type pillar insulators are mostly used in low-voltage distribution lines and communication lines, and rod type pillar insulators are mostly used in high-voltage substations.

Porcelain insulator
An insulator made of electrical ceramics. Electrical ceramics are baked from quartz, feldspar and clay. The surface of porcelain insulator is usually covered with enamel to improve its mechanical strength, waterproof infiltration and increase the surface smoothness. Among all kinds of insulators, porcelain insulators are the most commonly used.

Glass insulator
An insulator made of tempered glass. Its surface is in a compressive prestressed state, such as cracks and electrical breakdown, the glass insulator will spontaneously break into small pieces, commonly known as "self-explosion". This feature makes the glass insulator in operation without the need for "zero value" detection.

Composite insulator
Also known as composite insulator. The insulating part is an insulator composed of glass fiber resin core rod (or core tube) and sheath and umbrella skirt of organic material. It is characterized by small size, light weight, high tensile strength, excellent anti-fouling flasher performance, but the anti-aging ability is not as good as porcelain and glass insulators.
Composite insulators include: rod suspension insulator, insulation cross strut insulator, pillar insulator and hollow insulator (composite sleeve). Composite busings can replace porcelain busings used in a variety of power equipment, such as transformers, arresters, circuit breakers, capacitive busings and cable terminals. Compared with porcelain sleeve, it has the advantages of high mechanical strength, light weight and small size tolerance, but also can avoid the damage caused by explosion.

Low voltage insulator and high voltage insulator
Low-voltage insulators refer to insulators used in low-voltage distribution lines and communication lines. High voltage insulators refer to those used in high voltage and ultra high voltage overhead transmission lines and substations. In order to meet the needs of different voltage levels, different numbers of single (piece) insulators of the same type are usually used to form insulator strings or multi-section insulation pillars.

Stain resistant insulator
The main measures are to increase or enlarge the insulator umbrella skirt or umbrella edge to increase the creepage distance of the insulator, so as to improve the electrical strength of the insulator in the polluted state. At the same time, the structure shape of the umbrella skirt is changed to reduce the amount of natural fouling on the surface and improve the anti-fouling and flashover performance of the insulator. The creepage ratio of dirt resistant insulators is generally 20% ~ 30% higher than that of ordinary insulators, or even more.
In areas with frequent pollution flash in China's power grid, it is used to adopt pollution-resistant insulators with the shape of double-layer umbrella structure, which has strong self-cleaning ability and is easy to be cleaned manually.

Dc insulator
It mainly refers to the disk insulator used in DC transmission. Dc insulators generally have longer creepage distance than AC stain-resistant insulators, and their insulating parts have higher body resistivity (not less than 10Ω·m at 50℃). Sacrifying electrodes (such as zinc sleeves and zinc rings) should be added to their connecting fittings to prevent electrolyzing corrosion.

Type A and type B insulators
Type A is a non-breakable insulator, whose dry flange distance is not more than 3 times (pouring resin) or 2 times (other materials) of the dry flange distance; type B is a breakable insulator, whose breakdown distance is less than 1/3 (pouring resin) or 1/2 (other materials) of the dry flange distance. Insulator dry flashover distance refers to the shortest distance through the air along the outer surface of the insulation; Breakdown distance refers to the shortest distance through the insulation material.