A Study of the Direct Current Erosion Mechanism of Silicone Rubber Housing Composites for DC Outdoor Insulation
Jayaram, Sheshakamal and Cherney, Edward A. (Adjunct)
High voltage direct current (HVDC) can be an economical mode of transmitting power over long distances, but justification for its use must address the aspect of reliability. The reliable performance of outdoor insulators, which are recognized as the backbone components of the transmission line system, has accordingly become a crucial demand. Currently, outdoor silicone rubber (SiR) insulators are replacing the conventional ceramic insulators, as SiR housing materials have demonstrated an electrical performance superior to porcelain and glass. However, in polluted conditions, all SiR insulators are prone to dry-band arcing (DBA) eroding the housing material, which may lead to insulation failure and consequently interruption of the power supply.
Extensive investigation into the erosion mechanism has led to well-established formulations of SiR housing composites for AC outdoor insulation applications, but with lesser concern given to the case involving DC. In particular, composites that have been designed for AC are being applied to DC, with simple modifications of the insulation creepage distance or geometry and despite the very different DBA characteristics under DC as compared to AC. Such a practice sheds the light on the existing DC insulators as an unknown entity that requires further investigation in order to ensure the reliability of power supply, particularly with the increased interest in DC.
In this study a thorough investigation into the erosion mechanism of the DC DBA as opposed to AC DBA, for which the latter is understood, is presented. Such an understating requires building solid guidelines of evaluating erosion under DC and finding reliable indicators of the corresponding eroding DBA. To this end, the study will closely examine the role of inorganic fillers, which are vital for suppressing the effects of DBA, as a foundation for the development of polymeric composites for outdoor HVDC.