The effect of pressure on streamer inception and propagation in liquid hydrocarbons

High-speed electrooptical techniques are used to study prebreakdown behavior in n-hexane and toluene at pressures between 0.1 and 5 MPa. The results show that pressure inhibits the formation of low-density regions and increases prebreakdown inception voltage. The observed pressure effects suggest that the low-density region is the result of liquid vaporization near the electrode. Results obtained with a chopped voltage pulse indicate that the shape of the applied voltage is not critical to streamer growth. Streamers were observed growing after the voltage pulse had been removed, which suggests that the streamer growth process is: (1) to some extent locally controlled by the presence of injected charge, or (2) controlled by thermal expansion of the low-density region. It was also observed that the streamer would initiate, grow, and then disappear under impulse voltage conditions