振荡型有界波模拟器特性阻抗的计算及其影响因素研究

Calculation of the Characteristic Impedance and Analysis of Influencing Factors on Impedance for Oscillatory Bounded-wave Simulator

为了研究VFTO对GIS二次设备的影响,需要通过振荡型有界波模拟器对VFTO辐射场进行模拟。模拟器是典型的平板传输线结构,必须保证波的传播路径中特性阻抗连续才能防止发生波的折反射现象,为此需要确定特性阻抗的大小,文中将通过反射系数法对其进行计算。采用CST软件建立振荡型有界波模拟器的模型,在其首端施加上升沿极陡的阶跃信号,对工作空间中心点处的电场波形进行记录,得到入射波与反射波的幅度,根据反射系数与特性阻抗之间的关系可以对特性阻抗的数值进行计算。利用这一方法,分析过渡段长度和电磁场形成装置首末端尺寸对特性阻抗的影响。结果表明,通过反射系数法对特性阻抗进行计算准确度较高并且应用方便,过渡段长度和首末端尺寸均能够对特性阻抗造成影响,过渡段越长,首末端尺寸越小,波的传播路径中阻抗的一致性越好。

To understand the influence of VFTO on secondary equipment of GIS,oscillatory bounded-wave simulator is used to simulate the VFTO radiation field.The simulator has a typical structure of plate transmission line.Continuous characteristic impedance must be ensured in the wave propagation path to prevent the refraction and reflection of wave.Therefore,it is necessary to analyze the characteristic impedance.In this paper,the reflection coefficient method is adopted to calculate the characteristic impedance of the electromagnetic field forming device.A simulation model of the oscillatory bounded-wave simulator is established with the software CST.Applying a step signal to the simulation model,and recording the electric field waveform at the center of the work space,the amplitudes of the incident wave and reflected wave are obtained.According to the relationship between the reflection coefficient and the characteristic impedance,the value of characteristic impedance is calculated.Subsequently,the influences of the structural factors on the impedance are analyzed.The result shows that the reflection coefficient method is highly accurate and easy to be used,and the length of the transition section and the size of both ends of the electromagnetic field forming device affect the magnitude of the characteristic impedance.The longer the transition section or the smaller the size of both ends,the better the impedance consistency in the wave propagation path.