In the present work, prebreakdown phenomena in dielectric liquids which have various molecular structure, especially turning our attention to chlorine atoms or fluorine atoms and some double bonds included in moleculer formula, are observed in detail for positive and negative point polarities, under the application of an impulse voltage (1.1/225 μs) to the point electrode. As test liquids, cyclic hydrocarbon liquids such as cyclohexane, benzene, chlorocycl ohexane, monochloro benzene, hexafluorobenzene and cyclohexene, are used. Results obtained in these liquids are compared with ones obtained in straight-chain hydrocarbon liquids.
As a result, the propagation of negative streamers, especially in dielectric liquids with chlorine atoms or fluorine atoms in molecular formula, is promoted, on the other hand the propagation of positive streamers in dielectric liquids with some double bonds is promoted. The former is related to large electron affinity, the latter is due to π electrons, for both cyclic and straight-chain hydrocarbon liquids.