可替代型气制变压器油中流注传播模式转变的机理研究

In recent years, Gas-to-Liquid (GTL) transformer oil derived initially from natural gas is considered as an alternative to conventional mineral oil, and there is an increasing interest to study its insulation performance under high voltages and extreme conditions. In a practical liquid, breakdown in long oil gaps under high voltages is due to the development of fast streamers. Previous researches made by the applicant indicated that under positive lightning impulse voltages, the threshold voltage where streamer propagation transfers from slow streamer to fast streamer, is lower in GTL oil than that in conventional mineral oil. Under negative polarity, the threshold voltage is higher in GTL oil than that in mineral oil. The existing propagation model for fast streamers is unable to explain the differences in the transition of streamer mode between GTL oil and mineral oil. This project carries out experimental studies of the transition of streamer propagation mode in GTL oil under lightning impulse voltages. Physical properties for describing streamer shape changes during the transition process are observed. Electric field strength and energy dissipation at streamer tips introduced by ionization processes, as well as shockwave and pressure profiles inside streamer channels introduced by liquid superheating, are estimated quantitatively in order to describe the effects of electronic and thermal processes on the changing trend of streamer shape. Consequently, the physical nature of fast streamers is confirmed, so as the underlying mechanisms for the transition of streamer mode in GTL oil. The model for streamer propagation in GTL oil during transition process is also built up. Researches in this project can provide technical considerations for insulation design of GTL oil filled transformers as well as the identification of physical mechanisms involved in liquid discharge phenomena.

近年来以天然气为原料的可替代型气制变压器油在高电压和极端条件下的绝缘性能已成为研究热点。变压器实际运行中高电压下大间距油隙的击穿是由快流注发展导致的。申请人在前期研究中发现正极性雷电冲击电压下气制油中慢流注转变为快流注的阈值电压低于传统矿物油，负极性下气制油中快流注产生的阈值电压高于矿物油。然而现有的快流注发展模型无法解释气制油在流注传播模式转变过程中与矿物油存在的差异。本项目拟通过试验手段，在雷电冲击电压下详细研究气制油中流注在传播模式转变过程中的形态发展规律。定量分析电离过程导致的流注尖端场强和能量变化规律，以及热效应导致的流注通道压强和冲击波速度变化规律。明确电离过程和热效应在流注形态变化过程中的具体作用,探明快流注的物理本质,从而建立气制油中流注在传播模式转变过程中的发展模型。本项目的实施将为使用气制油的变压器绝缘设计提供试验基础与理论依据，并促进对液体电介质放电机理的进一步认识。

正极性雷电冲击电压下气制油中慢流注转变为快流注的阈值电压低于传统矿物油，负极性下气制油中快流注产生的阈值电压高于矿物油。然而现有的快流注发展模型无法解释气制油在流注传播模式转变过程中与矿物油存在的差异。. 本项目以雷电冲击下气制变压器油中的流注和激波为研究对象，利用阴影法测量研究气制油中慢流注和快流注的完整发展过程，并结合分形理论对流注形态结构变化进行量化分析。利用纹影法对流注传播过程中伴生的激波现象进行观测，并结合放电过程中光电信号的同步测量，分析热效应和电离过程在气制油预放电过程中的具体作用，提出气制油中快流注发展模型和传播模式转变机理。结果发现，气制油中慢流注的形态为气泡簇或分叉较多的树枝状，速度一般为亚音速，仅发出微弱光线。快流注的形态为分叉较少的树枝状，速度远远超过音速，且发出明亮光线。慢流注的发光由初始气泡膨胀过程中电子和能量的注入导致，流注的跃迁过程中发生的强烈电子-空穴复合导致了快流注的发光，快流注的电离程度远远大于慢流注。同时发现传导电流和场致发射电流的焦耳加热作用下，液体蒸发形成微气泡的过程在雷击电压下慢流注起始过程中起重要作用。快流注的形成还依赖于液体中原本存在的不可见微气泡以及强电场作用下局部液体破裂产生的空腔。在流注发展过程中，慢流注中微气泡的爆炸会先导致亚音速激波的产生，随后电离出更多的气泡产生气体通道，最终导致流注的形成。而快流注形成之后，初始电弧通道由于极高的温度和压强，向外急剧膨胀并产生超音速激波。. 项目从气制油的流注传播转变模式出发，探索了电离过程和热效应对流注发展的影响，拓展了高电压和极端条件下液体电介质击穿理论，为使用气制油的变压器绝缘设计奠定了理论基础。依托项目，共计发表了论文6篇。其中3篇期刊论文被 SCI 收录，1篇期刊论文被EI收录，2篇会议论文被EI收录；申请发明专利 2 项