Based on field ionizing mechanism,the mathematical model of the transformer-oil discharge in the needle-sphere electrode system is established and the special dynamic behaviors of the charged-particle generation,transportation and heated-diffusion during the discharge process are represented by the partial differential equations and boundary constraint conditions,then the breakdown characteristics of the transformer-oil dielectrics are achieved by the theoretical simulation under nanosecond impulse voltages.Modeling results show that streamer velocity of the transformer-oil dielectrics is increased with applied voltage amplitude increase,and the propagating distance of the negative streamer is less than that of the positive streamer along the axial direction and extends much more than that of the positive streamer in radial direction,and also the onset voltage of the negative streamer is higher than that of the positive streamer.The shorter time of the wave front of the positive impulse voltage,the bigger radius of the streamer development,then the streamer may be scattered and disappeared when raising time of the negative impulse voltage is less than the 50ns.The achievements and suggestions of the research work in this paper contribute to understand discharge mechanism of the liquid dielectrics,and have guiding significance for reasonably application and development liquid dielectrics in practice.%以针-球电极间隙变压器油为研究对象,基于场致电离机理,建立用于表述液体电介质流注预放电过程中载流子的产生及输运的偏微分方程,结合电场泊松方程,以及热扩散方程,仿真研究纳秒脉冲电压下变压器油预击穿特性.得到了预击穿过程中电场强度随电压幅值、极性以及脉冲上升沿时间的变化规律.仿真结果表明:流注速度随电压幅值的增大而增大;负流注相比于正流注轴向传播距离小径向传播距离大;负流注起始放电电压高于正流注,且起始速度大于正流注;正脉冲上升沿时间越短所形成流注半径越大,上升沿时间大于50 ns的负脉冲条件下产生的流注易消散.本文的研究工作和取得的结论有助于加深对变压器油中放电起始、发展过程的认识以及对液体电介质放电机制的理解.
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