Non-continuous Positive Leader Propagation in Sphere-Plane Air Gaps

The effect of a large series resistance on leader initiation and propagation in a large sphere-plane gap during switching impulse breakdown is an interesting topic since it can be used for studying air insulation physics. The series resistance inhibits discharges and is known to increase the 50% disruptive discharge voltage of an air gap and may therefore be useful for improving the insulation design of high voltage systems. In addition to improving the withstand voltage, the series resistor has also been observed to slow down the breakdown process. This effect has now been studied utilizing and ultrahigh-speed camera together with current measurements of the discharge events. A stepwise leader propagation is observed unlike any non-continuous positive leader propagation reported on in literature. A 0.5 m diameter spherical electrode was connected to a voltage divider and impulse generator via a 2.5 m long tunable water resistor. The sphere-plane gap was set to 2.4 m.