Advantages of Composite Insulator Compared with Porcelain Insulator and Glass Insulator
1. High strength, light weight.
The glass fibre core used in composite insulator has high axial tensile strength, generally 600 Mpa or above, 5-10 time higher than porcelain.
The gravity of the materials used in core and shed of composite insulator is around 2.0 kg/m3. The weight of a composite insulator of hundred kN rated charge is only 10-15% of the porcelain insulator.
2. High Pollution Flashover Voltage
A. The shed of composite insulator is made of silicone rubber. The surface of silicone rubber shed has a lower cohesive energy than water drop, and hence become hydrophobic. Under humid and polluted environment, the water drop cannot form a water film but only separated small drops. Due to this factor, the partial electric arc cannot be developed and result in a high pollution flashover voltage.
Silicone rubber contains some micro-molecules (CH3) which would spread out to the surface of the shed and decrease the surface energy of the pollution and enhance the hydrophobicity. This is technically called hydrophobic migration.
B. Long leakage distance. The thickness of the composite insulator is much thinner than that of porcelain insulator. The composite insulator could contain 2 time of sheds more than porcelain insulator. The more are the sheds, the longer leakage distance it is, and hence a much higher pollution flashover voltage.
C. The equivalent diameter of composite insulator is much smaller than porcelain and glass insulator. The surface resistivity of composite insulator is in inverse relation to the equivalent diameter. Even the lost of hydrophobicity, under the same electric resistivity, the surface resistivity of composite insulator is still much higher and its leakage voltage is much lower than porcelain and glass insulator, hence the pollution flashover voltage of composite insulator is much increased.
3. No need to test the null value. The composite insulator is in a post insulation structure, and has a nearly same distance between inner and outer pole. Generally no inner insulation breakdown happen and hence no need to test the null value. It is easy to maintain composite insulator due to its good performance in pollution flashover, no need to do cleaning to the pollution.
4. Silicone has excellent aging resistance, high and low temperature resistance, good tracking resistance and electric corrosion resistance.