The composite insulators were introduced in 1960s. Over 50 years of manufacturing, several standards and performance tests for these insulators introduced, new materials and composites developed and the manufacturing processes had improved. So nowadays these kind of insulators have been using all around the world because of their advantages to glass and porcelain insulators including their hydrophobic virtue, good action in contaminated areas, light weight, easy transmission and installing on electrical lines, high tensile and torsion strength and humidity resistance.
The structure of composite insulators consists of three main parts as shown in figure 1.
Figure1. Composite insulator structure
1. End fitting: The last part of an insulator in transmission line strings which joins other fittings. We manufacture insulators with a variety of different fittings such as socket, ball, clevis, tongue, y-clevis and eye, according to IEC standards (figure2). These fittings are forged steel based materials to obtain most high strength virtue.
Figure2. Different insulator fittings
(From left to right: eye, socket, clevis, ball, y-clevis and tongue fittings)
2. Composite rod: The composite part withstands torsion, tensile and compressive loads in an insulator. The rod material is a combination of 70-75 % fiber glass with epoxy or polyester resins. Fiber glass is distributed in longitudinal direction of insulator in a resin film and manufactured by pulltrusion process. Our Company has used these materials and manufacturing policy for composites to present high quality and strength products for customers all around the world.
3. Polymer sheds and sheath: The polymer layer around the composite part inhibits electrical conductivity in an insulator, so it should has a good resistance property to every environmental phenomenon that causes electrical conductivity such as rain, water drop, humidity, salt, sand and air pollution. The material in this part usually consists of a polymer like silicon rubber and filler like Aluminum tri hydrate (ATH). Fortunately the silicon rubber has a hydrophobic feature, means it fractures water flow to small drops and inhibits water to create a continuous flow along the insulator, and more importantly, it also transfer the hydrophobicity properties to the contamination in the upper layers. So it reduces electrical conductivity by water flow. Silicon rubber also has a good behavior in contaminated areas. By creating an appropriate sealing between Polymer sheath, composite rod and end fittings in manufacturing process, we will have a good humidity resistance as a result and again low possibility of electrical conductivity. We chose silicon material for insulators sheds and sheath to achieve these properties.
The sheds will be formed in our modern polymer molding machine to reach high quality products.