变压器中性点气水两相组合流体保护间隙的工频放电特性与机制研究

Research on Power Frequency Discharge Characteristics and Mechanism of the Protection Gap of the Combined Fluid of Air And Water Used on Transformer Neutral Points

为克服变压器中性点传统空气保护间隙存在的缺陷,提出了"气水间隙"概念,并在武汉大学电气工程学院高电压与绝缘技术试验室进行了气水间隙工频放电特性试验。试验结果表明:当水流从低压电极喷射到高压电极时,间隙很难击穿;当间隙总长度固定,工频放电电压随喷射水流长度减小呈先减小后增大的变化趋势;当喷射水流长度略小于间隙总长度时,工频放电电压与间隙总长度呈线性递增关系;同等长度的气水间隙比空气间隙和全水间隙易击穿,等等。基于气泡击穿理论和空气与水不同的电特性,对试验观察到的放电现象、规律和机制进行分析,指出水流的击穿起因是其中的"气泡桥"的存在和发展,以及水中电离子作用的结果;在气水间隙中,空气段率先击穿形成的电弧高温加热水流促使水中气泡的产生和发展,最终导致水流段的击穿;气水间隙放电特性曲线具有先减小后增大的变化趋势特征是空气和水流不同的电特性相互作用的结果;将气水间隙应用于变压器中性点保护,具有较可观的研究价值和应用前景。

To overcome the disadvantages of traditional protection air gaps of transformer neutral points, the concept of the gap of water and air was presented. The power frequency discharge test between the gap of air and water was conducted in high voltage test room of School of Electrical Engineering in Wuhan University. Test results show that breakdown of the gap is very hard to occur when flow is jetted to the high voltage electrode from low voltage electrode; power frequency discharge voltage will decrease first and increase then with flow length decreasing when the total length of the gap is constant; there is a linear increasing relation between power frequency discharge voltage and total length of the gap when the flow length is somewhat less than the total length of gap; breakdown of the gap of air and water can occur more easily than air gap and water gap of the same length. Based on the bubble breakdown theory and different electrical characteristics of air and water, the law and phenomenon obtained from the test is discussed theoretically from mechanism. It is pointed out that the breakdown of water flow results from existence and the development of ＇bubble bridge＇ and the effect of electric ion in water; in the gap of air and water, high temperature of arc generated from the first breakdown of air segment heats water flow to promote the generation and development of bubbles in water, and the breakdown of water flow segment can be generated finally; the discharge characteristics curve of the gap of air and water going down first and rising then results from different electrical features of air and water. The gap of air and water used on transformer neutral points protection has high research value and broad application prospect.