Silicone rubber (SiR) insulators were employed in power system due to its light weight, high electrical strength and excellent contamination performance. Much attention has been paid on the accurate evaluation of the insulator hydrophobicity. In this chapter, the acoustic characteristics of surface discharge were investigated to evaluate the hydrophobic properties of SiR insulator at different ageing degrees. The obtained results indicate that the acoustic characteristic of discharge is sensitive to the hydrophobic properties in the laboratory tests, which can be applied as a non-contact method for hydrophobicity evaluation of SiR insulator. Besides, the surface charge behaviors considering the hydrophobic properties of SiR insulator were discussed. The droplet experiment was carried out to investigate the maximum value, cumulative charge and energy eigenvector of discharge current. Finally, considering the strong airflow for SiR insulators employed in high-speed railway, the hydrophobic properties and corona discharge properties were investigated in this chapter.
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The ±800kV UHVDC transmission line is now in experimental operation in China (Shang, 2006; Shu et al., 2006). More than ninety percent of insulators used in the HVDC transmission lines are polymer insulators due to advantages of light weight and surface hydrophobicity (Nazir et al., 2016; Matsuoka et al., 2002; Fu et al., 2011). In these lines, corona discharge could occur even on well-designed hardware and insulators, and the corona can damage the polymeric insulators (Du et al., 2009; Liu et al., 2016; Fernando et al., 2010; Du et al., 2009; Baker et al., 2009; Rajini et al., 2009). Under dc voltage, compared with ac voltage, the electrostatic force due to the constant electrostatic field makes more ions bump against the insulator surface. By causing some chemical changes, significant material degradation will reduce the insulator surface hydrophobicity (Kim et al., 1994; Khattak et al., 2016). When insulators are exposed to long-term humidity and severe contamination, with the decrease of hydrophobicity, the conductive layer will be easily accelerated to form on the surface. Thus, leakage current will be driven to pass through the layer and cause the dry-band discharges (Lopes et al., 2002). When there is sufficient heat energy, UV radiation, acids etc. produced by the discharges, more molecular chains of silicone rubber will be broken, which induces severe surface deterioration. Due to the hydrophobicity loss and the development of discharges, flashover may take place and affect operating reliability of power system (Chandrasekar et al., 2009). From the viewpoint of safety and reliability, to develop methods for hydrophobicity evaluation of SiR insulators is mainly the basis for the insulation design and the reliable operation of power system (Sabri et al., 2010; Liu et al., 2010).