shaped protrusion in SF6 gas. The breakdown voltagetime (Vt) characteristics and the breakdown voltagegas pressure (Vp) char-acteristics of a highly non-uniform SF6 gas gap under positive and negative lightning impulse voltages are investigated in the...
shaped protrusion in SF6 gas. The breakdown voltagetime (Vt) characteristics and the breakdown voltagegas pressure (Vp) char-acteristics of a highly non-uniform SF6 gas gap under positive and negative lightning impulse voltages are investigated in the pressurerange between 0.1 and 0.5 MPa. The pre-breakdown developments are examined by the corona current and light emission measurementswith high time resolution. As a result, the dielectric strengths versus time-to-breakdown of SF6 gas gap under positive lightning impulsevoltages were nearly independent of the gas pressure. The rst streamer corona was initiated at the tip of the needle electrode, and thestreamer corona pulses developed with a stepwise propagation. The discharge paths were zigzag, and the branches of the discharge chan-nel for positive polarity were created. On the other hand, the leader channel in the negative polarity was thicker and brighter than that inthe positive polarity.