Insulators are devices installed between conductors with different potentials or between conductors and ground potential components, which can withstand voltage and mechanical stress.

Insulators play two basic roles in power system: one is to support conductors and bear mechanical stress; The second is to prevent the current from flowing or returning to the ground between conductors with different potentials and withstand the effect of voltage. It is combined with fittings to fix the conductor on the tower and reliably insulate the conductor from the tower. During operation, the insulator should bear not only the working voltage, but also the operating overvoltage and lightning overvoltage. In addition, the insulator should have good electrical insulation performance due to the dead weight of the conductor, wind force, ice and snow and the mechanical load of environmental temperature changes, At the same time, it shall have sufficient mechanical strength.

Classification of insulators

1. According to the insulating materials for manufacturing insulators, they can be divided into porcelain insulators, tempered glass insulators, synthetic insulators and semiconductor insulators.

2. It can be divided into breakdown type and non breakdown type according to whether the shortest puncture distance in the insulator is less than half of the flashover distance in the external air.

3. According to the structural form, it can be divided into column (pillar) insulator, suspension insulator, butterfly insulator, pin insulator, cross arm insulator, rod insulator and sleeve insulator.

4. According to the application, it can be divided into line insulator, power station insulator and electrical insulator. Power station insulator: used to support and fix the indoor and outdoor distribution of power plant and substation

The hard bus of the electrical device and insulate the bus from the earth. It is divided into post insulator and bushing insulator according to different functions. Electrical insulator: used to fix the current carrying part of electrical appliances. It is also divided into post insulator and bushing insulator. Post insulators are used to fix the current carrying part of electrical appliances without closed shell; Bushing insulator is used to lead the current carrying part of electrical appliances with closed shell (such as circuit breaker, transformer, etc.) out of the shell.

Line insulator: used to consolidate overhead transmission and distribution conductors and flexible bus of outdoor distribution devices, and insulate them from the grounding part. There are needle type, hanging type, butterfly type and porcelain cross arm.

5. According to the service voltage, it is divided into low-voltage (AC 1000 V and below, DC 1500 V and below) insulators and high-voltage (AC 1000 V and above, DC 1500 V and above) insulators. Among the high-voltage insulators, there are ultra-high voltage (AC 330kV and 500 kV, DC 500 kV) and ultra-high voltage (AC 750kV and 1000 kV, DC 800 kV).

6. It is divided into indoor type according to the service environment: the insulator is installed indoors, and there is no umbrella skirt on the insulator surface. Outdoor type: the insulator is installed outdoors, and there are many and large umbrella skirts on the insulator surface to increase the discharge distance along the surface, and block the water flow in rainy days, so that it can work reliably in harsh climate environment.

7. According to different functions, it can be divided into ordinary insulator and antifouling insulator.

Classification of insulators

1. High voltage line insulator

① Rigid insulators of high voltage line: including pin type porcelain insulators, porcelain cross arm insulators and butterfly type porcelain insulators. When in use, they are directly fixed on the tower with their own steel feet or bolts.

According to the structural form, porcelain cross arm insulators of high voltage lines can be divided into four types: all porcelain type, glue mounted type, single arm type and V-shape; According to the installation form, it can be divided into vertical type and horizontal type; According to the standard, lightning impulse full wave withstand voltage can be divided into four levels: 165kv, 185kv, 250kV and 265kv (originally, 50% full wave impulse flashover voltage can be divided into six levels: 185kv, 2l0kv, 280kv, 380kV, 450kv and 6l0kv). Porcelain cross arm is used in high-voltage overhead transmission and distribution lines, which can replace pin and suspension insulators, and reduce the length of pole and cross arm.

Butterfly porcelain insulators of high-voltage lines are divided into 6kV and l0kV according to the rated voltage. It is used for insulating and fixing conductors on overhead transmission and distribution line terminals, tension and corner poles. At the same time, it is also widely used to cooperate with line suspension insulator to simplify hardware structure.

② High voltage line suspension insulator: including disc suspension porcelain insulator, disc suspension glass insulator, porcelain pull rod and ground wire insulator.

High voltage line disc suspension porcelain insulators are divided into ordinary type and pollution resistant type. It is used for high voltage and ultra-high voltage transmission lines to suspend or tension conductors and insulate them from poles and towers. Suspension insulators have high mechanical and electrical strength. They can be applied to various voltage levels through different string groups and meet various strength needs. They are the most widely used. The ordinary type is suitable for general industrial areas. Compared with ordinary insulators, pollution resistant insulators have larger creepage distance and shape convenient for wind and rain cleaning. They are suitable for coastal, metallurgical powder, chemical pollution and more serious industrial pollution areas. When the pollution resistant insulator is used in the above areas, it can reduce the size of the tower and has great economic value.

The purpose of high voltage line disc suspension glass insulator is basically the same as that of high voltage line disc suspension porcelain insulator. Glass insulator has the characteristics of high mechanical strength, mechanical impact resistance, good cold and heat performance, long service life, excellent electrical performance and lightning resistance. When it is damaged during operation, its umbrella disc will be broken automatically, which is easy to find, greatly reducing the workload of insulation detection.

High voltage line porcelain pull rod insulator is used on the terminal pole, tension pole and corner pole of overhead power line with small cross-section conductor of l0kV and below as insulation and fixing conductor. It can replace some butterfly porcelain insulators and disc suspension porcelain insulators.

③ Rod type porcelain insulators for overhead contact system of electrified railway.

2. Low voltage line insulator

① Pin type, butterfly type and spool type porcelain insulators for low-voltage lines: pin type porcelain insulators for low-voltage lines are used for insulation and fixing conductors in overhead power lines below 1KV. Butterfly porcelain insulators and spool porcelain insulators for low-voltage lines are used as insulated and fixed conductors on power supply and distribution line terminals, tension and corner rods.

② Tension porcelain insulator for overhead line: it is used for balancing the tension of the pole at the terminals of AC and DC overhead distribution lines and communication lines, corners or long-span poles, so as to insulate the lower stay wire from the upper stay wire.

③ Insulator for tram line: used as insulation and tensioning conductor for tram line or as insulation and support for conductive part on tram and power station.

④ Pin type porcelain insulator for communication line: used for insulating and fixing conductor in overhead communication line.

⑤ Insulators for wiring: including drum insulators, porcelain splints and porcelain tubes, which are used for low-voltage wiring.

3. High voltage power station insulator

① High voltage indoor post insulator for power station: it is used on the electrical equipment bus and distribution device of indoor power station and substation with power frequency rated voltage of 6 ~ 35kV. As an insulating support for high voltage conductive part. It is generally installed at an altitude of no more than 1000m and the ambient temperature is - 40 ~ 40 ℃, and should be used without pollution and condensation. The specially designed plateau type can be used in areas with an altitude of 3000m and 5000m.

② Outdoor pin post insulator: it is applicable to the insulated part of electrical appliances or power distribution devices with AC rated voltage of 3 ~ 220kV, ambient temperature of - 40 ~ + 40 ℃ around the installation site and altitude of no more than 1000m. It is used as insulation and fixed conductor.

③ Outdoor rod post insulator: it is used for high-voltage electrical appliances and high-voltage distribution devices to insulate and fix conductors. It has largely replaced the use of outdoor pin post insulators.

④ Antifouling outdoor rod post insulator: suitable for salt coating density of 0.1mg/cm ² The medium pollution area within is used for the insulation and fixation of high-voltage electrical appliances and power distribution devices.

⑤ High voltage wall bushing: including indoor wall bushing, outdoor wall bushing, bus wall bushing and oil paper capacitive wall bushing.

⑥ Electrical porcelain bushing: including transformer porcelain bushing, switch porcelain bushing, transformer porcelain bushing, etc.

Transformer porcelain bushing includes bushing porcelain bushing and pillar porcelain bushing for power transformer and test transformer. Switch porcelain bushing includes porcelain bushing of multi oil circuit breaker, porcelain bushing of low oil circuit breaker, porcelain bushing of load switch, porcelain bushing of explosion-proof switch, porcelain bushing of disconnector, porcelain bushing of air circuit breaker, etc. It is mainly used as the insulation of the high-voltage lead of the switch to the ground and as the container for circuit breaker insulation and internal insulation. The porcelain bushing of transformer is used as the insulating element of current transformer and voltage transformer.