长空气间隙放电研究进展

Research Progress of Long Air Gap Discharges

长间隙放电研究是高压输变电工程的外绝缘设计和雷电屏蔽问题研究的基础。为此,从长间隙放电特性试验、长间隙放电机理和长间隙放电过程仿真模型等3个方面,概述了国内外工作者在长间隙放电研究上取得的成果。在此基础上,归纳分析了目前研究中存在的不足,认为:放电特性试验研究难以穷举实际输变电工程间隙,也无法准确获得实际过电压应力下间隙的绝缘特性;现有长间隙放电机理研究缺乏对流注区域空间电荷分布规律、先导通道特征参数的深刻认识,一些常见假设如流注几何形状和区域电场恒定、先导起始的临界温度及先导通道特性等,或没有测量证实,或带来与实际情况的较大偏差;空间电荷计算模型中不同的流注形状和电场分布假设,选取流注、先导的转换条件,以及将先导通道视为具有一定通道压降的导体,都使模型计算结果与试验测量值存有明显偏差。最后指出,在未来的相关研究中,应重视长间隙放电基础研究,深入开展长间隙放电观测技术和放电参数测量研究,获得流注空间电荷分布、流注-先导转换临界温度和先导通道电场与温度等关键特征参数,指导建立和完善长间隙放电仿真模型,以准确预测长间隙放电特性,最终实现输变电工程外绝缘精细化设计,同时为雷电屏蔽理论和模型的完善提供参考。

Researches on long air gap discharge are considered to be the basis of external insulation design for high voltage power systems and lightning-shielding researches. From three aspects, i. e. discharge tests, discharge mechanisms, and simulative discharge models, achievements in existing world-wide researches on long air gap discharge are summarized. Moreover, deficiencies of these researches are also investigated. It is indicated that experimental studies in laboratory could neither exhaustively reproduce all the gap configurations in actual high voltage power systems, nor obtain the characteristic of gap insulation subjected to actual switching overvoltage waveforms. The reported mechanism studies on long air gap discharge lacks deep understandings of space charge distribution in streamers and characteristic parameters of leader channel; besides, some common assumptions in these studies, for instance, the constant steamer shape and environmental electric field, the critical temperature of leader initiating and the characteristics of leader channel, are either short of verification from actual measurements, or the cause of some mechanism＇ s obvious disagreement over reality. As for simulative models, several factors, including different assumptions of streamer shape and electric field distribution in space charge models, the chosen conditions of streamer transforming into leader, and considering leader channel as conductor with certain voltage drop, could all lead to significant errors of the calculation results of models compared with measurement results. In the end, it is suggested that, for future studies, it is of great significance to focus on the fundamental study of long air gap discharges, especially on observation techniques and the characteristics of key parameters, aiming at obtaining important physical parameters, including the distribution of the streamer space charge, the critical temperature of streamer-leader transition, and the inner electrical field and temperature of leader channel. Consequently, long air gap discharge simulation models can be improved to accurately predict the breakdown characteristics of long air gaps, realizing the refined design of external insulation. The results can also provide valuable information for improving present theory and simulative models of lightning shielding.