10_sanquan_image_long_gap - 214 IEEE TRANSACTIONS ON PLASMA...

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Unformatted text preview: 214 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 38, NO. 2, FEBRUARY 2010 Observation of the Streamer–Leader Propagation Processes of Long Air-Gap Positive Discharges Shanqiang Gu, Member, IEEE , Weijiang Chen, Jiahong Chen, Hengxin He, and Guanjun Qian Abstract —A novel observation method is proposed to study the streamer–leader propagation processes of long air-gap posi- tive discharges. Experiments of 3–12 m air-gap discharges have been conducted in this paper. The observed images could clearly and particularly describe the characteristics of the positive streamer–leader propagation processes. Some important phenom- ena of the propagation processes are indicated and discussed, such as the leader’s velocity that varied with the time, the different lengths of inception leaders, the leader’s branching phenomena, the continuous streamer–leader propagation processes simulta- neously with the voltage’s descent, and the upward leader’s prop- agation processes. Index Terms —Discharge, high-speed video camera, impulse voltage, leader, long air gaps, streamer. I. INTRODUCTION T HE streamer–leader propagation process is an important phenomenon in long air-gap discharges under impulse voltages and is paid much attention to by physical scientists and power engineers. Over the last several decades, many laboratory experiments have been carried out to investigate this phenom- enon under different electric-field configurations, gap lengths, voltages, air pressures, etc. [1]–[7]. The studies are mostly aimed at discovering the discharge mechanism of long air gaps and making efforts to theoretically simulate the discharge processes. On the other hand, those studies are also seeking for the method on how to utilize the long air-gap discharges to simulate the processes of lightning strikes. In the experimental studies, the optical-image-observation system is one of the most important means to understand the physical morphology and propagation characteristics of the streamer–leader. The previ- ous observation methods for air-gap discharges are the paper film [8], rotating camera [9], etc., where the observation results were still very simple. Later, the photomultiplier [1] and image intensifiers [10] are applied and realize the photoelectric ob- Manuscript received October 3, 2009; revised October 25, 2009. First published December 15, 2009; current version published February 10, 2010. This work was supported in part by the National Natural Science Foundation of China (50737003) and in part by the Eleventh-Five Year Science and Technology Program of State Grid Corporation of China (SGKJ[2007]756). S. Gu, J. Chen, H. He, and G. Qian are with the State Grid Electric Power Research Institute, Wuhan 430074, China (e-mail: gushanqiang@ sgepri.com; chenjiahong@sgepri.com; hehengxin@sgepri.com; qiangj0124@ 263.net)....
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10_sanquan_image_long_gap - 214 IEEE TRANSACTIONS ON PLASMA...

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