Formation and characterization of dry bands in clean fog on polluted insulators

The formation and development of dry bands can best be studied by modifying the standard test procedures. When such controlled behavior is allied with synchronized optical and electrical recordings, then characterization of the pre-formative leakage current, the transient phenomena associated with partial arcs across dry bands, the location of partial arcs and the voltage drop across dry bands can be determined. Interpretation of test data is greatly aided by finite element computation of insulating structures with a conducting surface layer. When this layer is continuous, this allows straightforward prediction of dry band formation under wetting conditions. Following formation, dry bands can be represented by discontinuities in this layer. Simulation of dry bands with various lengths, when combined with the test data, enables partial arc voltage gradients to be quantified. These results will be discussed in the context of previous work on the pollution flashover mechanism of ceramic insulators.