Observation of a lightning flashover with a high-speed video camera

In this paper we analyze images of a lightning flashover induced by a downward negative lightning flash that struck a transmission line located in São Paulo, Brazil. The lightning flash and the flashover were recorded by a high-speed camera running at 10,000 images per second. The approach of the negative downward leader did not launch an induced positive upward leader prior to the return stroke. One of the AC transmission lines that run over a railway line was struck. The flashover exhibits an oscillatory behavior. The flickering of the image occurs at exactly 120 Hz. The return stroke that struck the line had an estimated peak current of a moderate intensity. It was however, followed by a continuing current lasting 17 ms and an intense M-component that may have contributed to the occurrence of the flashover.