直流GIL中自由金属微粒的放电特性及危险程度评估

发布时间：2019-04-29 18:28

【摘要】：自由金属微粒是制约直流气体绝缘线路(DC gas insulated line,GIL)绝缘耐受能力的重要因素。在电场力作用下,直流GIL中的自由金属微粒可运动至高压电极或绝缘子附近,引发局部放电或气隙击穿,对直流GIL的绝缘性能造成巨大的威胁。本文针对自由金属微粒运动引发的局部放电问题,结合其运动行为研究影响放电特性的因素以及危险程度判别。首先,采用同轴圆柱腔体和线形金属微粒为试验模型,搭建直流高压局部放电试验平台,针对电压极性、幅值、微粒长度、半径、SF6气压、微粒个数等影响微粒放电特性的因素开展直流高压试验。利用脉冲电流法及高速相机同时观察记录其局部放电信号与运动行为,对微粒的运动特性与放电特性进行分析,探究各因素对线性金属微粒的运动特性及放电特性的影响。其次,对影响微粒放电物理机制的因素进行深入分析,探讨不同因素的作用机理,并定量分析不同因素的影响。而后,利用COMSOL软件对不同长度、半径、位置的线性金属微粒对电场分布的影响进行仿真分析。最后,综合考虑试验、仿真结果以及放电机理,探究微粒的危险程度。结果表明:微粒的局部放电与运动活性随着直流电压幅值的提高而更加剧烈,由于直流极性效应,微粒在负电压作用下发生“飞萤”现象,在负电压下的局部放电较正电压下的更为剧烈,对绝缘的威胁更严重。随着微粒长度的增加,微粒的局部放电更加剧烈,而运动角度范围随之减小。随着微粒半径的提高,微粒的起跳电压升高,当半径大于一定值时,微粒保持静止,危险程度随之降低。随着气压增大,气体的局部放电随之减弱,微粒的运动范围减小,但绝缘效果有趋于饱和的趋势。多个微粒同时运动时,微粒的平均局部放电量略有提高,但放电频次明显增加,且在空气环境中,出现两个微粒在同一径向运动并引发串联气隙击穿的现象,危险程度增加。微粒对电场分布的畸变效应与长度呈正相关,与半径呈负相关,最大电场强度均出现在不与电极接触的一端,且与高压电极接触时的电场畸变效应最严重。因此,微粒的危险程度与其个数、长度呈正相关;当微粒的半径大于一定值时,微粒静止不构成危险,可进一步根据微粒的局部放电信号判断其危险程度及微粒长度。本文研究有利于深化微粒的放电物理机制的研究,为进一步实现危险程度评估定量化分析提供了一定的理论指导。
[Abstract]:Free metal particles are important factors that restrict the insulation tolerance of DC gas insulated lines (DC gas insulated line,GIL). Under the action of electric field force, free metal particles in DC GIL can move to the vicinity of high voltage electrode or insulator, causing partial discharge or air gap breakdown, which poses a great threat to the insulation performance of DC GIL. In this paper, according to the problem of partial discharge caused by the movement of free metal particles, the factors affecting discharge characteristics and the discrimination of risk degree are studied in combination with their motion behavior. Firstly, using coaxial cylindrical cavity and linear metal particles as experimental models, the DC high voltage partial discharge test platform is built, aiming at voltage polarity, amplitude, particle length, radius, SF6 pressure. The DC high voltage test was carried out for the factors affecting the discharge characteristics of the particles, such as the number of particles. The pulse current method and high-speed camera were used to observe and record the partial discharge signal and the motion behavior of the particles. The motion characteristics and discharge characteristics of the particles were analyzed and the effects of various factors on the motion characteristics and discharge characteristics of the linear metal particles were investigated. Secondly, the factors influencing the physical mechanism of particle discharge are analyzed deeply, and the action mechanism of different factors is discussed, and the influence of different factors is analyzed quantitatively. Then, the influence of linear metal particles with different length, radius and position on electric field distribution is simulated and analyzed by COMSOL software. Finally, considering the experiment, simulation results and discharge mechanism, the dangerous degree of particles is discussed. The results show that the partial discharge and motion activity of the particles are more intense with the increase of DC voltage amplitude. Due to the DC polarity effect, the particles appear "firefly" phenomenon under the negative voltage action. Partial discharge under negative voltage is more severe than that under positive voltage, and the threat to insulation is more serious. With the increase of particle length, the partial discharge of particles becomes more intense and the range of motion angle decreases. With the increase of the particle radius, the take-off voltage of the particle increases. When the radius is larger than a certain value, the particle remains stationary and the dangerous degree decreases. With the increase of the gas pressure, the partial discharge of the gas decreases and the moving range of the particles decreases, but the insulation effect tends to saturate. When several particles are moving at the same time, the average local discharge of the particles increases slightly, but the frequency of discharge increases obviously. In the air environment, two particles move in the same radial direction and cause the breakdown of the air gap in series, and the danger degree is increased. The distortion effect of particles on the distribution of electric field is positively correlated with the length and negatively with the radius. The maximum electric field intensity appears at the end without contact with the electrode, and the electric field distortion effect is the most serious in contact with the high voltage electrode. Therefore, the danger degree of particles is positively correlated with the number and length of particles, and when the radius of particles is larger than a certain value, the particles are not dangerous at rest, so the danger degree and the length of particles can be further judged according to the partial discharge signal of particles. The research in this paper is helpful to deepen the research on the physical mechanism of particle discharge and provide some theoretical guidance for the further quantitative analysis of risk assessment.
【学位授予单位】：华北电力大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM75

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