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 t he pre-formative leakage current, the transient phenomena associated with p artial arcs across dry bands, the location of partial arcs and the voltage drop across dry bands can be determined. Interpretation of test data is gre atly aided by finite element computation of insulating structures with a co nducting surface layer. When this layer is continuous, this allows straight forward prediction of dry band formation under wetting conditions. Followin g 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 are voltage gradients to be quantified. These results will be discussed in the context of previous work on the pollution flashov er mechanism of ceramic insulators.