Comparative Study of Streamers＇ Characteristics in Different Seed Based Insulating Oils under Lightning Impulse Voltages

This paper is aimed at the streamers in natural esters (vegetable oils) in point?plane electrode arrangement under lightning impulse voltage. The shape, stopping length, velocity and current of streamers are investigated. Six untreated commercial oils extracted from grape seeds, sunflower and rape seeds, corn, rice and sesame that could constitute potential liquids for high voltage applications are tested. A naphthenic mineral oil is also tested for comparison. It's shown that the streamers are filamentary for both polarities. For a given voltage, the stopping lengths (Lf) of streamers are longer when the point is positive than when it is negative; also, except mineral oil when the point is negative, the values of Lf are very close in all tested oils. The streamers' velocities are in the same range for all vegetable oils and they vary between 0.4 km/s and 1.2 km/s for positive polarity and 0.2 km/s and 0.8 km/s for negative polarity.