Insulators are used to insulate the electrically charged part of any machine or equipment from other uncharged metal material or charged part. One other purpose of the insulator is that it keeps the live conductors unreachable by completely covering it from the human being and other animals. On the other hand, at high voltage overhead transmission and distribution, the transmission towers or poles carry the line, and insulators play their part by insulating the live conductor from the transmission towers. These insulators also bear a large tensional and compressive load of the transmission and distribution systems.
According to the materials used, the HV/EHV insulators are divided into two broad types. Those two types are Ceramic and polymer insulators. The latter ones are also called composite insulators.
Now, composite insulators are constantly getting famous and the use has increased in high voltage transmission systems. These insulators contain a fiber rod surrounded by an outer casing of some polymer. The hydrophobic nature of the surface of the insulators allows it to create discontinuities in the wet creepage path. This property makes these insulators the best performer in polluted and coastal areas. One other advantage of the composite insulators is that it is very light in terms of weight than porcelain insulators.
There are different types of insulators used in the transmission and conductors’ support.
- Pin Type Insulators: Pin type is the first type of the insulators that are being used for overhead lines. The voltage grade limit for these insulators is up to 33kV. The top of the insulator is connected with the live conductor, while the bottom of the insulator is connected to earth. When the insulator gets wet, its outer surface becomes conducting, which decreases the flash over the distance of the insulator. All the electrical insulators are designed to get the minimum decrease of flashover distance when the insulator is wet. So, the uppermost part of a pin insulator is designed like an umbrella to protect the rest lower parts from the rain.
- Post Insulators: Suitable for higher voltage, post insulators come with more numbers of petticoats and have a height greater than pin type insulators. This type can be used horizontally as well as vertically on different supporting structures. Two or more of these insulators can be used for higher voltage application to attain the needed requirement.
- Suspension Insulators: In this type, disc insulators are connected in series to make a string. The numbers of discs change according to the voltage grade, which makes it suitable for many voltage levels.
- Strain Insulators: In strain insulation, suspension string is used to support the tensile load of the conductor. Each disc of the insulator is designed for 11kV.
- Stay Insulators: These insulators are for low voltage lines. The insulator in the stay wire is also called stay insulator.
- Shackle Insulators: Shackle insulators are used in the low voltage distribution network and can be placed both in horizontal and vertical positions.
Well, despite these, there are many more, which you would require to know, just Google for more help.