Corona behaviour in a 0.5 m conductor-rod gap under composite switching impulse/alternating voltages

The corona behaviour in the conductor-rod gap, under composite 119/2350 μS or 342/2500 μS impulse/alternating voltages near 50% composite sparkover voltage is described. It is shown that with increasing AC pre-stressing voltage, the time to first corona decreases and the composite voltage at first corona along conductor increases as the positive switching impulse is triggered at the points of 90, 135 and 180 degrees. These correspond to increases in 50% composite sparkover voltage associated with greater numbers of the corona pulses occurring along the conductor, compared with the simple switching impulse alone. When the positive corona occurs at the rod before breakdown, the 50% composite sparkover voltage tends to decrease compared with the simple negative impulse alone, under negative switching impulse