Assessment of positive lightning breakdown voltage of selected ester liquids in point-to-sphere electrode system

This article presents the results of the measurements of lightning breakdown voltage of three different commercial dielectric liquids of different chemical composition: two natural esters and one synthetic ester. The measurements were performed in point-to-sphere electrode system which is recommended by the IEC 897 standard. The voltage supplied was a positive standard lightning impulse 1.2/50 μs. A gap distance was 25 mm and a method of breakdown voltage estimation was a step method with 5 kV voltage increment. The results showed that the differences between the liquids tested exist. The average value of breakdown voltages from 20 measurements was the highest for one of the natural ester (marked as natural ester I) with simultaneous the highest value of time to breakdown. This means that in the testing conditions applied in the studies presented, in a non-uniform electrical field at positive standard lightning impulse voltage, this type of the ester is characterized by the best lightning strength.