Spatial-temporal investigation of breakdown of long air gaps by lightning voltages up to 2.4 MV

The breakdown behavior of long rod-Plane air gaps by Lightning Impulses (1.2/50 μs) has been investigated and the results of a new measurement system are reported in this paper. A series of up to eight photos (made by a high-speed camera) have recorded the expansion of discharge activities during the breakdown process. The pre-discharge current and voltage have been measured as well. The modern measurement techniques have made possible the synchronization of the photos with the current and voltage measurements in nanosecond-ranges. The combination of the measured current, voltage, and photos can precisely explain the breakdown process. The experiments have been carried out with the lightning impulses up to û=2.4 MV and the air gaps up to s=4 m. Despite of such high voltages, the experimental system has been verified to be appropriate for measuring the pre-discharge current in mA-ranges.