Application of dimensional analysis to flashover characteristics of polluted insulators

In the paper, the method of dimensional analysis is applied to determine the flashover characteristics of polluted insulators. Expressions deduced for the flashover voltage in a d.c. circuit under simplified conditions are found to agree with the analytical findings of previous authors. The work is then extended to flashover characteristics in a.c. systems, where the dynamic properties of arcs are introduced. It is found that the same functional dependence of the flashover voltage on pollution and insulator characteristics prevails as for d.c. conditions, although the magnitude of the flashover voltage may be different in the two cases. Finally, an expression for the velocity of arc propagation along the polluted insulator surface is deduced with due consideration of insulator, layer and circuit parameters. Of special interest is the dependence of the ultimate arc velocity on the short-circuit current of the test circuit, as well as the expression for the minimum voltage necessary to start arc motion. Whenever possible, the analyses included in the paper are compared with previous field and/or laboratory experience.