Overhead line insulators are used for transmission, distribution lines and electrical traction lines. The design can be different for each application and the product range is wide depending on the dimensional, mechanical and electrical requirements.
Pin Insulators are the earliest developed overhead insulator but are still used commonly in power networks up to 33 kV systems. Pin type insulator can be one part, two parts or three parts type, depending upon application voltage. It is desirable to increase the vertical length of the insulator surface area for lengthening leakage path as the leakage path of the insulator is through its surface. One or two or more rain sheds or petticoats are provided on the insulator body to obtain a long leakage path.
Post Insulators are similar to Pin Insulators but are more suitable for higher voltage applications. Post insulator comes with a much higher number of petticoats and a greater height compared to pin insulators. This type of insulator is very easy to mount on supporting structure horizontally as well as vertically. The insulator is made up of one piece of porcelain and it has clamp arrangement are in both top and bottom end for fixing. It can be a single stag as well as multiple stags. The conductor is fixed on the top of the insulator with help of connector clamp, two or more insulators can be fixed together one above other for higher voltage application.
In higher voltage, beyond 33KV, it becomes uneconomical to use pin insulator because size, the weight of the insulator becomes more. Handling and replacing bigger size single unit insulator are quite a difficult task, for overcoming these difficulties, disc insulator was developed. In disk insulators, a number of insulators are connected in series to form a string and the line conductor is carried by the bottom-most insulator.
In case of low voltage lines, the stays are to be insulated from the ground at a height. The insulator used in the stay wire is called the stay insulator and is usually of porcelain and is so designed that in case of breakage of the insulator the guy-wire will not fall to the ground.
Usually in a low voltage distribution network, the shackle insulator is normally used. It can be used in both the horizontal or vertical positions. The use of such insulators has decreased recently after increasing the usage of underground cable for distribution purpose.