Streamer Charging of Dielectric Barriers in Inhomogeneous Air Gaps - Measurements of Surface Charge Depositions

Abstract

The purpose of this thesis is to conduct experiments on a rod-plane gap, with and without a dielectric barrier. The gap is connected to an impulse generator, which stresses the gap with a lightning impulse triggering streamers in the gap. The residual charge left by streamers can be measured with a nullifying probe. Two different laboratory set-ups are used. One with a grounded plane and the other upside-down with a grounded rod. Cameras able to take a trigger pulse was added to the grounded-rod set-up, but due to electric noise and other problems with the camera set-up, the camera ended up never working properly. The grounded-plane set-up, on the other hand, has a working camera and the possibility for measuring residual charge left on the barrier.

The residual charge, measured after streamers have shattered charged particles all over the barrier, shows that the shape of the residual charge curve was either bell-shaped or saddle- shaped. If the residual charge is saddle-shaped, back-discharges are visible in the PMT-signal. The saddle-shape is present when the barrier is close to the rod and/or the applied voltage is high.

Pictures taken of streamer activity in the gap show that a bright channel sometimes ignites after a streamer has developed in the gap. The bright channel looks more like a leader than a streamer. The rod-plane gap where this leader-type channel is observed is 80 mm or shorter. Leaders are traditionally only observed in gaps longer than 1 m.