THE EFFECT OF PRESSURE ON STREAMER INCEPTION AND PROPAGATION IN LIQUID HYDROCARBONS

High-speed electro-optical techniques are used to study pre-breakdown 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 the low-density region is the result of liquid vaporization near the electrode. Results obtained with a chopped voltage pulse indicate 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 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. In cases when the streamers disappeared before the impulse voltage had decayed to zero and the voltage was subsequently ‘chopped’ (i.e. the potential difference between the two electrodes was rapidly returned to zero), new streamers would appear. The second appearance of the streamers indicates that charges remains in the pressurized liquid after the streamers disappear and that they return to the injecting electrode when the voltage is chopped. The physical appearance and growth behavior of the second streamer are similar to that recorded during initial formation and growth of a positive streamer. © 1990 IEEE