Pre-breakdown and breakdown mechanisms of an inhibited gas to liquid hydrocarbon transformer oil under negative lightning impulse voltage

In this paper, streamer and breakdown phenomena and their mechanisms of an inhibited Gas-to-Liquid (GTL) transformer oil under standard negative lightning impulse voltages were studied. A conventional inhibited mineral oil was also tested as the benchmark. Experiments were carried out in 25 mm and 50 mm point-plane gaps. Streamer and breakdown phenomena of both oils were observed from the streamer inception voltage level up to the voltage level at which fast streamer appears with a velocity of over 10 km/s. The results showed that the GTL oil has a higher breakdown voltage and a higher acceleration voltage compared to the mineral oil. This is due to the fact that the GTL oil has a much lower aromatic content compared to the mineral oil. The streamer investigations showed that the development of fast streamers in both oils is the consequence of transition from dark streamer channels to bright streamer channels. By comparing with the results obtained under positive polarity [1], the differences in the propagation mechanisms between the fast negative streamers and fast positive streamers were explained.