Porcelain was at one point the main insulating material for electrical equipment like transformers and switchgears and was used in transmission lines. However, despite the advantages of its high insulation strength, it has a low strength to weight ratio and is prone to fragmentation under stress.
Advances in technology have given us a more cost effective choice with the advancement of polymer insulators. Polymer materials have a higher insulation value that is the same quality of porcelain with acceptable strength when it comes to compression and tension. Polymer insulators are also capable of working in contaminated and polluted environments because of their water and sleet shedding properties.
Although the cost of both porcelain and polymer materials are the same, polymer is often favored because of the handling. This is because polymer insulators are a lighter weight than porcelain while still producing the same function. The weight of suspension of a polymer insulator in the 138 kV class is only 8% of the porcelain insulator of the same voltage power.
With the polymer insulators, a fiberglass insulation rod or shaft serves as the internal rod of the internal structure, much like the shape of a petticoat. In this design, the fiberglass rod has a high compression and tensile strength and the metal fittings at both the ends are crimped directly to the fiberglass rod. Proper sealing is done to avoid access of moisture or contamination into the fiberglass rod.
The time in which petticoats dry up is crucial and depends on a number of factors such as the contamination level in the area, the temperature, the humidity and the wind velocity after bad weather. If an area is has extreme contamination, polymer insulators with various petticoat sizes are used to obtain a greater distance between outer edges which helps avoid flashover.
Polymer insulators are suitable for high voltage applications of ethylene propylene (EP) and silicon rubber (SR). Ethylene propylene polymer has a higher resistance to corrosion and a better physical property while silicon rubber has a better performance under contamination. Silicon rubber also offers a higher resistance to ultra violet sunrays. A combination of EP and SR polymer has better hydrophobic, electro-mechanical properties and high resistance to industrial pollution. This is perfect for use in bushings of transformers, reactors, switchgears, and much more.
Polymer insulators are most frequently used on suspended lines that have a dead end or carry a tension load, as well as being incorporated into lines that join two lines together. They might also be used to control conductor spacing. Northern Power only carries the best polymer insulators and we only work with the best companies. For more information on power equipment, visit our blog more often!