Uniform field breakdown in SF6 gas at high pressures under lightning and switching surge voltages

Experiments were conducted to determine the 50% flashover voltages (V₅₀) over the pressure range of 0.14 to 0.45 MPa absolute, using lightning (1.2/50 μs) and switching (100/2500 μs) impulse voltages, under uniform electric fields having two electrodes of Rogowski profile, with a gap spacing varying from 4 to 30 mm. Results indicate that the breakdown strength of SF₆ gas exhibits slight saturation at higher pressures (above 0.3 MPa). The effect is higher for switching surge voltages than for impulse voltages. The polarity effect is observed both under lightning and switching surge voltages and is more pronounced at higher gas pressures and larger gap spacings. The V₅₀ values with switching surge voltages are generally lower than the corresponding lightning impulse voltage values