ELECTRONIC AND GASEOUS PROCESSES IN THE PREBREAKDOWN PHENOMENA OF DIELECTRIC LIQUIDS
Résumé
The article shows experimentally the simultaneous influence of electronic scavenger additives and the hydrostatic pressure on the current and emitted light by streamers, especially in cyclohexane under negative polarity. This suggests that both electronic and gaseous mechanisms do not act singly in the prebreakdown phase of dielectric liquids. A relationship between the streamer current, the electrical charge, the velocity, and the propagation mode of streamers is discussed. Based on energy considerations, we establish a mathematical expression allowing us to evaluate the velocity of streamers and to explain the propagation modes. The streamer the current of which consists of discrete pulses moves by steps. The higher the number and/or the amplitude of the current pulses, the shorter the durations between these steps and the higher the average velocity of the streamers; its propagation tends to become continuous. That is the case of the slow streamers in the presence of electronic scavenger additives. On the other hand, the streamer becomes rapid then more energetic and the hydrostatic pressure necessary for its disappearance increases. That is why it is thought that both gaseous and electronic processes simultaneously act in the prebreakdown phase even if one of them is dominant in one case and the second in another.