椭球电极负电晕放电的数值仿真研究

Numerical Simulation Study on Negative Corona Discharge of Small Ellipsoidal Electrode

电晕放电的研究对深入理解高压电气设备内部各种缺陷的电晕放电机理有着重要的意义。耦合流体动力学方程和泊松方程,建立了椭球电极的负电晕放电模型,应用有限元方法分析了放电电流脉冲和正离子数密度分布,首次通过数值仿真分析了椭球电极环模式放电。研究了不同施加电压及电极形状对椭球电极负电晕放电的影响机理。结果表明,施加的电压、电极形状对椭球电极负电晕放电电流脉冲数、脉冲波形特性及放电脉冲模式等有很大的影响。

Corona discharge is a common partial discharge that may occur in important power transmission equipment such as transformers,circuit breakers and gas insulated switchgear(GIS),causing serious damage to the insulation of the equipment.In recent years,researchers have studied the mechanism of negative corona discharge of electrodes with different tip shapes by numerical simulation.But there is no research on the negative corona discharge of small ellipsoidal electrodes.In this paper,the negative corona discharge model of ellipsoid electrode is established by coupling the fluid dynamics equation and Poisson equation.The discharge current pulses and the distribution of positive ion concentration are analyzed by using the finite element method.The ellipsoid electrode is equivalent to a symmetric simulation model.The model is placed in a simulated air domain with a side length of 10 mm,and the bottom of the simulation domain is a ground plane electrode with a radius of 10 mm.The ellipsoid electrode is located 3.3 mm above the ground plane electrode.After setting the initial density distribution of electrons and positive ions,and determining the discharge voltage and simulation time,the current pulses during the negative corona discharge can be obtained.In this way,an axisymmetric ellipsoid electrode negative corona discharge model is formed,which greatly reduces the simulation time.The lengths of the ellipsoid electrode half-axis a and b are set as 0.35 mm and 0.25 mm,respectively.By applying DC voltage,the ellipsoid electrode potential is-4.2 kV,and the simulation time is set as 20000 ns.The results show that only the first current pulse is the point discharge pulse appearing at 0°position(point A)of the ellipsoid electrode,and the other current pulses are the ring discharge pulse appearing near 90°position(point C)of the ellipsoid electrode.The amplitudes of all ring discharge pulse currents are greater than that of point discharge pulse currents.The shape of the ellipsoid electrode is kept unchanged,and the applied voltage is set to 3.6,3.7,3.9,4.1 and 4.2 kV,respectively.The simulation time is 20000 ns.The results show that the amplitude of the first current pulse of the ellipsoid electrode increases with the increase of voltage.The higher the applied voltage,the more current pulses during the negative corona discharge of the ellipsoid electrode.But the effect of the applied voltage on the negative corona discharge mode is small.The shape of the ellipsoid electrode is changed by keeping the applied voltage constant.Given that a is always greater than b,the results show that the smaller the ratio of half-axis a to b of the ellipsoid electrode,the more current pulses during negative corona discharge of the ellipsoid electrode.The greater the ratio of half-axis a and b of the ellipsoid electrode,the greater the proportion of the number of ring discharge pulses to the total number of discharge pulses.Therefore,changing the shape of the ellipsoid electrode not only changes the number,amplitude and occurrence time of current pulses during negative corona discharge,but also changes the discharge mode.The following conclusions can be drawn from the simulation analysis:(1)The ring mode discharge mainly occurs at the position where the electric field intensity is maximum before the pulse current.The greater the ratio of half-axis a to b of the ellipsoid electrode,the greater the electric field intensity at point C,and the greater the proportion of the number of ring mode discharge pulses to the total number of current pulses.(2)The greater the applied voltage to the same ellipsoid electrode,the earlier the first current pulse appearing and the greater the amplitude.(3)The number,amplitude,occurrence time and discharge mode of current pulses during discharge of ellipsoid electrodes with different shapes are different.