Weighting method for transient analysis of underground cables

Accurate computation of electromagnetic transients for underground cables and overhead transmission lines requires the frequency domain characterization of two matrix functions: propagation and characteristic admittance. The propagation function constitutes a high order wideband system with inherent time delays. In this paper a weighted fitting technique is presented and advocated for the identification of the propagation function as a rational transfer function. The paper also contributes to theoretical clarifications on vector fitting and orthonormal vector fitting. The application of orthonormal vector fitting is demonstrated together with weighted vector fitting. Although the presentation is also applicable to transmission lines, the numerical examples are focused on underground cables where the frequency dependency problems are more complex.