Prebreakdown and breakdown mechanisms of an inhibited gas to liquid hydrocarbon transformer oil under positive lightning impulse voltage

This paper presents experimental studies on streamer and breakdown phenomena and the mechanisms of an inhibited Gas-To-Liquid (GTL) transformer oil under positive lightning impulse voltages. A conventional inhibited mineral oil was also tested as the benchmark. Point-plane configurations with gap distances of 25 mm and 50 mm were used. 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 velocity over 50 km/s. The results showed that the GTL oil has a higher breakdown voltage but a lower acceleration voltage than 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. Based on detailed characterizations of the transition process, a model considering charge splitting and amplification processes was proposed to explain the underlying mechanisms.