Modelling of dry-band discharge events on insulation surfaces

Discharges on composite insulator insulation surfaces are one cause of long-term ageing. Consequences of such ageing are further acceleration of damage, and ultimately an increased likelihood of flashover. Normally it is an unacceptable flashover probability that requires maintenance or replacement of aged insulators. In some cases however, the surface discharges can lead to deep erosion which can then lead to of the surface being penetrated. This can result in moisture penetration into the core and internal tracking and permanent insulator failure. For these reasons modelling of discharge activity is important to understanding ageing processes. Here we show that the dynamic behaviour of moisture on the surface of an insulator is critical to its ageing. Circumstances are identified in which very rapid ageing can take place. The thermal properties of arcs are also shown to be non-linear. Experimental evidence from testing in salt fog chambers is presented and used to quantify the description of energy available for the degradation process. Using these experimental results, arc power and energy are analyzed as functions of arcing length. Causes for unusual heating of the polymer substrate, which ultimately damages the insulation material more rapidly than otherwise expected, are also identified.