Insulators are materials which restrict the passage electric current. They behave exactly opposite to that of conductors (Conducting materials).
Do you think a power system is possible without Insulators?
The answer is Impossible. If there are no insulators, there would be conductivity with the ground causing the system
I hope now you are clear with Insulator meaning.
Let us see the rest of the things about Insulators.
Properties of Insulators
The following are few of the properties of an Insulator.
- The first and foremost property of an insulator is to provide electrical insulation which means the non-conducting function. Example: Insulators are used in a Transmission line to prevent the flow of electric current between Transmission Tower and Transmission Line.
- They should be mechanically strong against Wind, Rain, Heat.
- The Insulation resistance should be very high in order to resist the leakage current.
- The insulators should not have any cracks, holes, and poles.
- The temperature change should not affect the functioning of insulators.
Materials used in Insulators
Porcelain, Glass, and Synthetic Resins are some of the widely used Insulating materials.
Porcelain is one of the most commonly used insulating material for transmission purposes. It comes under the ceramic material. China clay is used as a prime material in the manufacturing of porcelain. The Clay powder, silicon, and feldspar are mixed and processed in mills. Then the resultant is heated under the high temperature in a controlled furnace.
Then the certain shape has been provided for the porcelain and finally, it is covered with the glaze. The Galvanized iron is used as metal parts by which one porcelain insulator section is joined by another insulator section.
Next the insulator piece is heated further to make it mechanically stronger. At last the resultant piece is sent for testing where it is checked for quality.
A good insulator must have higher insulating resistance and it should be free from pores and cracks.
The Dielectric Strength of Porcelain Insulator is 12 MV/m.
Glass is also an example of insulating material. Glass is manufactured by the process called annealing.
Advantages of Glass Insulators
- Due to the transparency nature, any cracks and defects in the Glass Insulator can be found easily.
- The Dielectric Strength of Glass Insulator is 14 MV/m which is higher than the Porcelain Insulator.
- Glass Insulators are cheaper than porcelain insulators.
Drawbacks of Glass Insulators
- Comparatively weaker than porcelain.
- Irregular molding is not possible.
The compounds of rubber, silicon, and resins are used to manufacture synthetic resin insulators. This kind of insulators is mostly used for indoor units and not for outdoor units.
Different Types of Insulators
The different types of Insulators are
Pin type insulators
Pin type insulators are suitable for the lower voltages of 11kV and they are used as a single piece. For higher voltages like 22kV, 33kV pin type insulators are available as a single piece.
The pin types insulators are mostly restricted up to 33kV as it becomes bulky more than that.
At the top of the pin type insulators lead screws are provided in order to prevent direct contact with the metal. In addition to that 4 to 5 turns of binding wire are wrapped in the top conductor and they are made of copper or aluminium.
Rain sheds or Petticoats are provided at the outer layer to keep the insulator stable even during the rain.
Suspension type insulators
Pin type insulators are not economical for high-level voltages and also they are also bulky when it comes to high voltages. In this case, suspension type insulators are preferred.
From the name itself, anyone can guess that the suspension types insulators are freely suspended. This suspension type insulator is designed in a way that a single unit can be connected with another unit in a series and the total unit can be suspended freely.
Suspension type insulators further classified into two types.
- Cemented cap type
- Hewlett or inter-linking type.
Cemented cap type
In this type, a cast-iron holder is provided at the top of the insulator. At the bottom, space is provided so that another unit can be connected using a steel wire spring ring.
Hewlett or inter-linking type
In this type of insulator, a “U” shaped connector is provided so that another unit can be bolted. The top unit is connected to the tower arm and the lower unit hold the conductor.
Both types are made of porcelain.
Advantages of Suspension type insulator
- For voltages higher than 33kV suspension type insulators are preferred over pin type insulators as they are highly economical.
- Insulator for higher voltage can be easily attained by interlinking the individual insulator unit.
- In the case of a single unit failure, that particular unit can be replaced whereas in pin type insulator the entire unit has to be replaced.
- If the line voltage has to be increased in the future, extra units can be added with this assembly to withstand the increased voltage.
- Here the conductor is at the lower end and the earth arm is at the higher end. In the case of lightning, the surge current will pass through the earthed arm and the conductor won’t get affected. (Note: The lightning will attack only at the higher end)
Strain insulators are used in the areas where there is no possibility for a normal transmission tower like the dead-end of the transmission line, line crossing the river, slopy region, and hilly stations.
In the previous case, that is suspension type insulators are held vertically whereas in the case of strain insulators they are held horizontally.
Strain insulators are used for higher voltages where the condition exists.
Shackle Insulators can be used vertically, horizontally, aerially and in the dead ends. Spool Insulator is the other name for Shackle Insulator and they are usually bulk in size. They are used in the distribution line where there is a need for the angle change.
Egg insulator is also called as a stay insulator. The image for stay insulator is shown below.
The stay insulator is made of porcelain. In order to provide insulation in the stay wire between the pole and the stay clamp stay insulators are used.