Breakdown Phenomena in SF6 and Very Inhomogeneous Large Rod-Plane Gaps under 50 HZ-AC and Positive Impulse Voltages

Results of breakdown measurements in SF6 are presented using very inhomogeneous large rod-plane gaps, 50 Hz ac and impulse voltage at pressures from 0.05 to 0.6 MPa. It is shown that for both voltage forms breakdown occurs over the whole pressure range due to a transition of the discharge mechanism from streamer to leader development. It was possi ble to determine the leader inception voltage. The minimal possible breakdown voltage of such large inhomogeneous gaps is practically independent of pressure over a range from 0.3 to 0.6 MPa and can be described by a simple empirical re lationship as a function of the gap width.