Ice accumulation on high voltage insulators can cause accidents by flashover across the ice-covered insulators. The ice accumulation can be reduced by changing the insulator surface properties by application of a semiconducting RTV silicone coating. This method is based on the hydrophobicity and semiconductivity properties of the coating. The mechanism for reducing ice accretion is analyzed theoretically. Experimental results are presented to validate the effectiveness of the semiconducting RTV coating at reducing ice on insulator strings. The results show that the coating on the insulators delays ice formation and reduces the amount of ice.

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The corona onset voltage (COV) for bare overhead bundle conductors for transmission lines has been investigated using numerical calculations and the gas discharge theory. First, an accurate numerical method, the charge simulation method, was used to calculate the electric field distribution in the vicinity of bare sub-conductors in bundles. Then the electric field values and a criterion from the gas discharge theory were used to evaluate the onset voltage for negative coronas on the bare sub-conductors. The COVs obtained are in good agreement with literature data for laboratory models and full-scale test lines. Some numerical results for the COV for six-bundle conductors are also discussed.

In this study, the corona onset voltage (COV) of bipolar bare overhead bundle conductors for transmission lines has been investigated using numerical calculations and gas discharge theory. First, an accurate numerical method, the charge simulation method, was used to calculate the electric field distribution in the vicinity of bare sub-conductors in bundles. Then, the electric field values and a criterion from the gas discharge theory were used to evaluate the onset voltage for monopolar positive or negative coronas on the bare sub-conductors. The monopolar criteria for single conductors have been further developed for use in bipolar bundle conductors with a rational demonstration. The bipolar COVs obtained are in good agreement with the literature data for laboratory models and full-scale test lines. Furthermore, some numerical results for the COVs influenced by the different effect factors of the bundle conductors have also been discussed.