Search

SF 6 /N 2 mixtures is considered as a practical alternative proposal of SF 6 in GIS and GIL. Simulating particle transportations and chemical reactions during the positive streamer propagation in SF 6 /N 2 mixtures assists in the insulation performance optimization of SF 6 /N 2 mixtures. This paper presents a fluid dynamic model coupled with the chemical reaction system for the positive streamer propagation in SF 6 /N 2 mixtures. The Townsend coefficients of the 20%SF 6 /80%N 2 mixture derived from the proposed chemical reaction system are in accordance with the measurement results. Based on this model, the propagation of the positive streamer in a 1 mm needle-plate gap in the 20%SF 6 /80%N 2 mixture is simulated. Simulated results indicate that there exists a negative space charge region in the streamer channel. It can be attributed to the increasing attachment rates of SF 6 yielding SF 5 − and SF 6 −, and the reduction of the ionization rates of N 2 and SF 6 in the streamer channel. Besides, it is noted that the ionization activities of N 2 and SF 6 at the streamer head are equally important to support the continuous propagation of the positive streamer. The ionization of N 2 in the streamer channel serves as an important factor to supply electrons and avoid the accumulation of the negative space charge. [ABSTRACT FROM AUTHOR]

Experiments on leader development were carried out in 10 m and 6 m rod-plane gaps under positive impulse. Leader propagation was recorded by high speed CCD camera. Effect of branching on its channel tortuosity was studied based on these high speed photographs. Over 70% of turning points along the 2-D leader channel are accompanied with leader branching in the experiment. That is branching makes an important contribution to the channel tortuosity of positive leader. [ABSTRACT FROM AUTHOR]

Positive leader current spikes were observed in long air gap discharge. However, there has been no explanation on this phenomenon so far, and some leader advancement models can only produce the current without spikes. Therefore, it is necessary to figure out this phenomenon in order to deepen the understanding of leader discharge. In this paper, experiments of leader development were carried out in a 10 m rod-plane gap under positive switching impulse. The discharge current and high speed photographs of discharge process were recorded synchronously. Then the high speed photographs during the period when the leader current fluctuated were carefully analyzed. The experimental results showed that the leader current spikes were with leader branching. Finally, the effect of branching on the spikes of positive current was explained qualitatively and a hypothesis on leader branching was proposed. [ABSTRACT FROM AUTHOR]