The salt-fog test that is described in IEC Standard 1109 has provided engineers with a simple but effective method of assessing the tracking and erosion resistance of polymeric insulation. It is essentially a test of the material but recent workon composite insulators constructed with either EPDM, RTV silicone or HTV silicone sheds has shown that the procedures can also be used to assist in the design and construction of insulator units. The importance of having correctly designed terminationsand void-free mouldings has been revealed and finite element analysis confirms that insulators employing poorly designed terminations incorporate high stresses that lead to partial discharge activity and premature failure.
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