Abnormal polarity effect in nanosecond-pulse breakdown of SF6 and nitrogen

• Subnanosecond- and nanosecond-pulse breakdown characteristics in SF6 and nitrogen are investigated.
• The polarity effect in point-to-plane gaps of subnanosecond- or nanosecond-pulse breakdown is studied.
• The inversion of polarity effect takes place not only in SF6, but also occurs in nitrogen.

The breakdown of gas gaps in an inhomogeneous electric field at subnanosecond and nanosecond voltage pulse rise times are studied, and the famous polarity effect in point-to-plane gaps is investigated. It is shown that at a voltage pulse rise time of ∼0.5 ns, the inversion of polarity effect takes place not only in electronegative gases such as SF6, but also occurs in electropositive nitrogen. The inversion of polarity effect is related to a delay of electron emission from the plane cathode on arrival of the ionization wave front anode to the cathode. It is found that with a voltage pulse rise time of ∼0.5 ns, the inversion of polarity effect occurs at SF6 and SF6–N2 pressures of 0.25 MPa and lower, and with a voltage pulse rise time of 15 ns, at a SF6 pressure lower than 0.12 MPa.