Impact of carbon particles on the electrical strength 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 flashover behaviour 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 compared to technically clean oil under ac stress the presence of carbon particles in the oil can lead to a significant increase of the breakdown strength of the open oil gap and the flashover voltage of all investigated materials. Furthermore the contribution displays that in carbonized oil the probability of a surface degradation by a flashover is for all investigated solid materials higher than in clean oil indicating that due to the carbon particles the discharge propagates closet to the solids´ surface than in clean oil. Depending on the respective spacer material the remaining electrical strength after a surface erosion may thus be more reduced in carbonized oil but will still be lying on a higher level than in technically clean oil