Impact of carbon particles on the impulse flashover behavior of different solid/liquid interfaces in a non-uniform field

This paper reports on experimental investigations dealing with the influence of carbon particles on the lightning impulse flashover behavior of the interface between insulating rods of different permittivities and surface structures and transformer oil in a non-uniform electrical field. The results reveal that for negative lightning impulse stress carbon particles in the oil act as defects due to their positive polarity and thus reduce the breakdown and flashover strength of all investigated materials distinctly. For positive impulse polarity no significant detrimental impact of the carbon particles on the electrical strength can be made out. Furthermore the contribution displays that in clean oil as well as in carbonized oil the probability of a surface tracking is for all investigated spacer materials markedly lower at positive impulse polarity than at negative lightning impulse stress.