Flashover behavior of conducting particle on the spacer surface in compressed N/sub 2/, 90%N/sub 2/+10%SF/sub 6/ and SF/sub 6/ under lightning impulse stress

This paper deals partly with the influence of the gas pressure on the effects of surface conditioning in compressed N/sub 2/ gas, 10%SF/sub 6/+90%N/sub 2/ mixture and pure SF/sub 6/ gas up to 730 kPa. This influence is investigated using a cylindrical spacer model with an adhering particle on the surface under homogenous field conditions. The influence of the particle position on the spacer surface and voltage polarity was investigated for lightning impulse voltages stress. The particle initiated flashover field strength relative to clean spacer was even discussed for investigated gases and three particle positions. The results of the investigations show that for an increase in steps of lightning impulse voltages, the spacer surface with a conducting particle can present higher flashover voltage. This behaviour can only be found out when the flashover does not occur at the first impulse but at other following impulses. Furthermore, as expected, the number of applied impulses each voltage step has certainly no significant influence on the flashover voltage. According to the voltage polarities and particle position, the observed flashover voltage and field strength in N/sub 2/ gas show no similar behaviour as in 10%SF/sub 6/90%N/sub 2/ mixture and in pure SFs gas for a gas pressure range of 100 to 730 kPa. However, particles sitting on a spacer surface can be detected with high probability by LI testing for all investigated gases.