Overhead insulators used for transmission lines rated 500kV and above, are relatively long, and the voltage distribution along the insulator length generally is non-uniform. Even though contamination of the outdoor insulator due to pollution is one of the prime factors leading to flashover and the resulting transmission line faults, it has been observed that the flashover can occur even before the presence of actual contaminants. In practice, the presence of water droplets over the insulator surface creates locations of high electric field intensity, a region where the electrical breakdown can initiate. The degree of field intensification at the triple point between water, air and insulator is a function of the wettability of the insulator surface, which increases with insulator degradation. In this work, the variation of electric field distribution around a typical water droplet in the sheath and shed regions as a function of the contact angle is reported. Two types of commonly used insulating materials namely hydrophobic silicone rubber (SIR) and porcelain have been investigated in our study.
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