A simple electronic technique for measuring streamer velocities in insulating liquids and gases

The measurement of streamer velocities in insulating liquids and gases requires considerable apparatus and knowledge, and cannot be considered a laboratory routine. Velocities in some liquids have been estimated using high speed cameras and photocells1 or by the use of Lichtenberg figures2 and chopped impulse waves, but even in these cases, the values quoted are considered approximate. With the present-day trend to more compact HV apparatus and use of new dielectrics, it would appear that a simple technique for assessing streamer velocities would be worthwhile. It is believed that such a method, which only utilizes apparatus common to most HV laboratories and employs small (<30 mm) electrode spacings, is now available. This technique was recognized by the author during a recent investigation of the charge and energy associated with ac point-to-insulated plane discharges in mineral oil, when it was noted that the value of positive streamer velocity estimated from the current pulse rise time for a small gap agreed closely with published data1, 3 for gaps near 100 mm. This encouraged an examination of streamer propagation in other insulating liquids and gases.