Measurement of Streamer Propagation Velocity over Solid Insulator Surface in a C4F7N/CO2/O2 Mixture under Lightning Impulse Voltages

For a better understanding of the discharge development over a solid insulator surface, experiments are conducted over epoxy-anhydride resin samples in a C
₄
F
₇
N/CO
₂
/O
₂
mixture under lightning impulse voltages. A measurement method of streamer propagation velocity using a photomultiplier is presented. It is observed that the propagation velocity greatly depends on the gas nature, the polarity of the voltage, and the high voltage electrode geometry. The involved mechanisms in propagation are also discussed.