Abstract: Abstract: In order to explore the characteristics and typical influential factors of fierce wildfires developed from ignition of typical forest vegetation materials via accidental faults inducing discharge breakdown processes of simulated broken and fallen segments of high voltage transmission lines(steel bar electrodes), a platform of such case was self designed to perform simulation experiments. Corresponding discharge and ignition experiments of simulated broken and fallen power lines were carried out on eucalyptus leaves, tuber fern chips, cedar pine needles and poplar chips under different gaps. Results show that the discharge inducing ignition stages can be summarized as "two phases and two points" (discharge induction period, gap breakdown point, arc induction period and fault removal point) when there is a proper gap between the simulated broken and fallen lines and the vegetation surfaces. There is no fault removal point in case of direct contacts. The possibility of ignition of the above four vegetation materials by the discharges is as follows: cedar pine needles>eucalyptus leaves≈poplar chips>tuber fernchips. With increasing water contents, eucalyptus leaves can still be ignited and the breakdown voltages required for discharge inducing ignition gradually decrease. For different forest ground vegetation types, under proper gaps and moisture contents, once they are ignited by the discharges between simulated broken and fallen lines and the vegetation materials, ignition and sustained flames will be produced, the formations of streamer channels will be promoted and the discharges and burning processes will be further aggravated until a wildfire is possibly triggered.

Key words: Key words: transmission line, fault of broken and fallen line, forest vegetation, wildfire, ignition, breakdown voltage, streamer, discharge