正极性纳秒脉冲电压下变压器油中流注放电仿真研究

建立了二维轴对称流体模型, 仿真研究了正极性纳秒脉冲电压下变压器油中针-板电极流注放电的起始与发展过程, 得到了不同的外施电压幅值、脉冲上升沿时间与电极间隙距离下油中流注放电的形貌、 电场强度与空间电荷密度分布等. 仿真结果表明: 空间电荷加强了流注头部前方电场, 使流注通道更易于向前推进, 形成"电离波"; 随着外施电压幅值升高, 流注发展的平均速度显著变大; 较陡的脉冲上升沿形成的放电半径较大, 对应的最大电场强度值变小; 随着电极间隙距离的增加, 流注发展平均速度变快. 仿真显示纳秒脉冲下放电中油温无明显升高, 表明此类放电过程没有明显的油气化现象. 我们认为, 场致电离是油中带电粒子产生的主导机制; 空间电荷效应增强流注前方电场使得电离进一步发展, 最终导致击穿. 本研究有助于加深对变压器油中放电起始、发展直至击穿过程的认识以及对液体电介质中电离机制的理解. 关键词： 变压器油 流体模型 流注放电 空间电荷效应

Simulational study on streamer discharge in transformer oil under positive nanosecond pulse voltage

In this paper, we investigate the streamer discharge process in transformer oil under positive nanosecond pulse voltage through developing a two-dimensional axially symmetric fluid model and simulating the physics of discharge inception and propagation. The streamer discharge profile and distributions of electric field and space charge density are obtained under different conditions such as the amplitude of applied voltage, rise time and gap distance. Simulation results show that space charges enhance the front field of streamer head, which is conducive to the longer propagation of discharge channel, therefore "ionization wave" is formed. The magnitude and rise time of applied voltage have evident influences on the average speed of streamer propagation. It can be observed that the higher the applied impulse voltage, the faster the streamer propagates, and the steeper the rise time of applied impulse, when streamer arrives at the same position, the larger the discharging radius will be and the smaller maximal electric field will be. The cases of different gap distances indicate that longer gap distance corresponds to a faster average speed of streamer. It is considered that field-dependent molecular ionization predominates the charge generation mechanism of streamer discharge process in transformer oil, and space charge effect contributes to further developing ionization until the whole gap eventually breakdowns. The study is dedicated to the better understanding of the process from inception to breakdown of discharging in transformer oil, as well as ionization mechanism in liquid dielectric.
Keywords： transformer oil fluid model streamer discharge space charge effect