Experimental study on surface flashover of a coaxial cable under nanosecond impulse voltage

The flashover of the polyethylene surface of a coaxial cable is studied under nanosecond impulse voltage. The rise time of the applied voltage is 50 ns. The average impulse flashover voltage per unit length along an insulation length (D) of 5 to 15 cm is measured to be 6.5 to 3.5 kV/cm. The delay time of the flashover is in the range of 500 to 700 ns. The velocity of the propagation of discharge is measured to be (2±0.5)×10⁷ cm/s at D=12 cm. In order to compare with the DC values, the DC average flashover voltage for unit length is measured. It is 7.8 to 5.8 kV/cm for D=5 to 15 cm. The voltage time curves of the flashover along the polyethylene and a pressurized spark gap are also given