Criteria for channel heating breakdown under non-uniform electric field in air

Summary

We focus on the breakdown mechanism in air due to channel heating, which tends to occur in a short gap length under a non-uniform electric field. The channel heating breakdown may occur with the rise of the channel temperature. In order to clarify the breakdown mechanism due to channel heating in dry air, in this paper, we discuss the channel heating energy to be closely related to the channel temperature. We observed applied voltage and discharge current waveforms with fast-framing images of the discharge in dry air at 0.1 MPa by applying a positive impulse voltage to needle-plane electrode system with the gap length of 15–30 mm. In the short gap length in air, a primary streamer from the needle electrode reaches the plane electrode, then a secondary streamer occurs. After several secondary streamers arrive at the plane electrode, the current concentration occurs in the shortest channel, and the other channels diminish. Current continues to flow in the shortest channel, and the channel is heated. If the conductivity of the channel becomes sufficiently high by the heating, the breakdown occurs. On the other hand, if the shortest channel diminishes before the conductivity of the channel becomes high enough to lead the breakdown, then the breakdown does not occur. On the basis of the above possible breakdown mechanism due to the channel heating, we controlled the discharge current by changing a limiting resistance of the impulse generator. Then, we investigated the energy criteria of channel heating leading to breakdown. The longer the gap length was, the larger the energy criteria became. The streamer channel diameter increased as the gap length increased due to the radial diffusion. In addition, the energy criteria did not depend on the limiting resistance, namely the current during the channel heating. This result implies the existence of energy criteria for the channel heating breakdown in dry air, and the criteria is almost determined by the input energy density.

Additional informations

Authors

LOPES, BARROS, TULIUS, MELLO, WOLF, Pozzati

Keywords

dry air, lightning impulse voltage, streamer, channel heating, breakdown