Breakdown and flashover in electronegative gas mixtures-insulator evaluation, time lag and impulse ratio measurements

Considering first the impulse ratio measurements and Figure 3, the following definitions are made: the breakdown voltage (V) is the peak voltage, the time to breakdown (t) is the duration of the approximately linear portion of the wavefront extrapolated back to the time axis (corresponds to the 10% voltage level) and teff is the time above 63 % of the peak voltage level. Figure 4 summarizes the results. As the rate of voltage application is increased, the time to breakdown decreases (from 5 μs to 330 ns) and the breakdown voltage increases (from 200 kV to 292 kV). If the “impulse ratio” is defined as the ratio of impulse breakdown voltage to dc breakdown voltage then it is seen to vary from 1.05 to 1.5 as the effective time (teff) of the pulse is reduced from 2.9 μs to 90 ns. In all cases the standard deviation of the breakdown voltage was less than 5% and the variation in time to breakdown was not measurable on the trace.