Accurate Transmission Line Modeling Through Optimal Time Delay Identification

-Frequency dependent transmission line modeling by the Method of Characteristics requires to calculate a rational approximation of the characteristic admittance Yc and the propagation function, H. Most models rely on fitting the modal components of H in order to handle the delay terms of the line. This paper compares various techniques for delay extraction and fitting with emphasis on accuracy and computational efficiency. The comparison includes asymptotic magnitude fitting, phase reconstruction from magnitude data followed by vector fitting (VF), and VF with time delay included in the optimization. The latter approach is shown to be the most accurate, at the cost of longer computation times. The alternative fitting strategies are applied to one example of transient overvoltage calculation on an underground cable system.