The voltage-time characteristics of the corona onset and breakdown of (SF6/Ar) mixture gas, in a high-field composed by a small needle-plane gap, were investigated experimentally under various positive and negative rectangular pulses with wave fronts of microseconds. As in the case of pure Ar gas, the corona onset and breakdown voltages in (SF6/Ar) mixture containing a small amount of SF6 gas decreased with increase in the wave front. However, for further increase in the content of SF6 gas, the breakdown voltage increased with increasing wave front and reduced on further increase in the wave front. This particular V-t curve could be seen with a small amount of SF6 under a negative needle than positive. The polarity effect with higher voltages under a negative needle was also seen on both corona onset and breakdown in the needle-plane gap. These anomalous V-t curve of mixtures are compared with those obtained under sphere-plane gap and are discussed on the basis of prebreakdown corona characteristics.
