FLASHOVER MECHANISM OF HIGH VOLTAGE INSULATORS

Flashover phenomenon is achieved through two successive phases: (1) appearance of a discharge at the surface of the wet insulator; (2) elongation for flashover if the conditions are favorable. The elementary phenomenon involved in flashover of high voltage insulators is the propagation of a discharge at the surface of an electrolyte. The study reveals two requirements: 1-Electrical conditions (applied voltage and discharge current) have to be fulfilled so that the discharge can be sustained by the power source throughout the elongation process. 2-A physical mechanism has to be shown which ″pulls″ the discharge and leads to flashover when the required conditions are met. The critical conditions are analyzed by a graphical method, using an electrical model. The physical mechanism is studied; it is shown through a set of experiments that it is an electrostatic force, acting on the discharge column. The macroscopic origin of this force is the perturbation of field distribution caused by the current flow in the liquid. The microscopic mechanism of interaction between the field and the discharge has yet to be analyzed in detail; a dielectrophoretic effect is nevertheless proposed which is the action of a divergent field on a dipole distribution.