Development of indigenous composite long rod insulator for high voltage transmission

Insulators form an integral part of electrical power transmission system. They are used to of fer mechanical support to the conductors and also isolate the live conductor from other parts from the safety point of view. Conventionally, ceramic and glass insulators have been in use for over a century and their performance has been well established. But for their brittle nature making them vulnerable to vandalism and handling difficulties, they are excellent insulators with very long service life and performance. With the ever-increasing demand for power, however, the transmission line voltages are getting increased thereby warranting the need to increase the creepage distance and also the tower size in order to meet the electrical clearance requirements. This poses serious problems. Increasing the creepage distance requires additional disc insulators added to the insulator string. This reduces the line-to-ground clearance demanding changes to the tower and this activity is expensive.

As a result of research all over the world, new polymeric materials are available in the market for various electrical applications. One such material is the silicone rubber, which is being extensively used for making the new class of non-ceramic insulator. This material too has advantages and limitations. ERDA has developed 66 kV suspension type insulator using commercially available silicone rubber compound and the same has been field-tried. A new rubber formulation has also been developed using indigenous raw materials with a view to make insulator with improved tear resistance. Detailed evaluation of the material and testing of insulator have been carried out. Failure of two insulator samples has been reported after 20 months of field trial at one of the locations. The causes of failure and other test results are presented in the paper.