Photographic investigations of electric discharges in Sandy media

Abstract

A complementary work to the accompanying paper of discharges properties in sand is presented here by means of photographing techniques. Photographic records of electric discharges in sand of three types are displayed. A few pictures were recorded under DC voltages. Most of the investigation was for lightning impulses. Streamer paths were recorded for very dry sand (large resistivities) and wet sand (low resistivities). Under DC voltages photographic cameras were mainly used. When applying lightning impulses the recording was made by placing X-ray sensitive films along the paths of the discharges. The observed features of the streamers are briefly described. A rare and new type of discharge has been observed. Positive streamers initiated at a certain radial distance (low field region) from the conductor and propagated towards the central conductor (high field region). This mechanism took place only for larger sand particles and application of negative lightning impulses under high resistivities of sand. Clear differences between the streamers were found, specially for high resistivitis. The discharging shapes were mainly dependent on the particle size and the impulse polarity.