Negative Creeping Discharge along Aerial Insulated Wire in Wet Condition

Aerial insulated wires are supported by postinsulators and binding wires on reinforced concrete poles. When a lightning flash strikes near by the wires, an overvoltage due to the indirect lightning surge is induced in the conductive wire core. A creeping discharge can develop along the wire surface from the free end of the binding wire through the postinsulator and reinforced concrete pole if flashover occurs at the postinsulator, and this also leads to wire damage such as melting or snapping. This can occur under either rainy or thunderstorm conditions. In this case, it indicates that the wire surface is stressed by lightning impulses under wet condition. Consequently, it is important to prevent wire damage and to clarify the characteristics of creeping discharges along the wire surface under dry and wet conditions. In previous investigations, we observed the characteristics of creeping discharges along wire surfaces under dry conditions. In this investigation, we examined creeping discharges under both impulse voltages with various wave front durations and wet conditions on the wire surface. These voltages were applied to the conductive wire core as inductive lightning surges. The duration and phenomena of negative creeping discharges developing along the wire surface were measured using a still camera with an image intensifier. We report the characteristics of the development of negative creeping discharges along wire surfaces under wet condition.