Development of Composite Insulators for Overhead Lines
Cables and insulators are the two aspects of overhead power transmission lines. Conventionally the insulators are made of ceramics polymer and glass. These materials have outstanding insulating properties and weather resistance, but also have the disadvantages: heavy, easily fractured. Therefore there was a desire to develop new materials that could overcome these disadvantages.
The 1930s and 1940s the first insulators appeared that organic material replaced the inorganic materials, but these have problems in weather resistance, and their characteristics were not suitable for outdoor use.
In the 1950s epoxy resin insulators were developed, but disadvantages were heavy, suffered from UV degradation and tracking, and so they were never put into actual service.
By the mid-1970s a number of new insulating materials had been developed, and the concept of a composite structure was advanced, with an insulator housing and a core of fiber-reinforced plastic (FRP), that is rudiment of composite insulator.
Since these materials were new, however, there were many technical difficulties that had to be remedied, such as adhesion between materials and penetration of moisture, and the end-fittings, which transmit the load, had to be improved.
Since the 1980s, Because of its weather resistance, virtually permanent, and its hydrophobic properties, allowing improvement in the maximum withstand voltage of pollution, and this had led to an explosive increase in the use of composite insulators.
In 1980, Furukawa Electric developed composite insulators
that had advantages of light weight and flexibility.
In 1991 the first composite insulators having silicone rubber housing were used as inter-phase spacers for 66kV duty,.
And in 1994 the voltage of composite insulator was extended to 275kV with the length 7m/unit--the world’s largest. With a view to cutting transportation costs, simplifying construction work and reducing the cost of insulators, more and more engineers considerate composite insulator as suspension insulators.
Later Furukawa Electric developed suspension composite insulators and delivered the 154kV tension insulators and V-type suspension insulator strings to Japan.
Now the pin type, post type, DS type, line post type, cross-arm type and rail way type have been developed , and more and more composite insulators are used all over the world.