Streamers in transformer oil initiated by partial discharge in a bubble at low AC electric fields

The possible mechanisms of electrical breakdown of transformer oil at low voltage values at alternating voltage were investigated. The formation of streamers from the surface of bubbles into a liquid dielectric after partial discharge in a bubble was detected. This phenomenon has been observed for bubbles in pure transformer oil, in transformer oil with the addition of carbon nano-tubes, in oil after operation. At very low voltages, streamers in transformer oil were registered if a partial discharge in the bubble was stimulated by X-rays. Three possible mechanisms of electric breakdown of a gap filled with transformer oil were revealed at low values of electric field strength in the range from 13 to 51 kV/cm. The appearance of streamers from bubbles was preceded by deformation of the bubble due to one or more partial discharges in it. Streamers always appeared in pairs from the poles of the bubble except for the case of the transformer oil with carbon nanotubes. The results obtained are important for understanding the mechanisms of breakdown of transformer oil at very low voltage and can explain the causes of a number of accidents in high-voltage installations.