Lightning-induced fault current arcs to communication cables buried in sand near overhead electric power lines.

摘要

A lightning stroke to an aerial electric power line may cause severe damage to a communications cable buried beneath it by initiating a fault current arc through the earth from the pole's ground electrode to the cable shield. The damage caused through this mechanism is much more significant than that caused by either a direct stroke to the cable or through a ground electrode that is not associated with an electric power line. This is due to the fact that a large amount of energy is available from the power line when a fault current arc is initiated to the cable.;The existence of the phenomenon was confirmed in initial tests performed on cable samples buried in a sand-filled cubical steel vessel 2 m on a side. A single soil electrode was subjected simultaneously to lightning impulses from a 3 MV Marx generator and 60 Hz power from a 1500 kVA, 15 kV transformer.;The ratio of fault current arcs to applied impulses as a function of power voltage and cable-to-soil electrode clearance was then examined more closely in a smaller soil container in which conditions could be more precisely controlled.;The apparatus was designed to allow rapid data acquisition. Sufficient data was accumulated to write an empirical formula for the damage radius around a power line ground electrode and to propose a model of the power arc inception mechanism in sand.