This paper describes a speedy method for calculation of frequency-dependent series impedances of the underground power cable in a tunnel. These impedances are needed for the analysis of electromagnetic transients and EMC in power systems. A technique based on the fictitious medium concept is used to calculate the magnetic vector potential exactly at several single frequencies in the tunnel, which reduces the solution region inside the poorly conducting earth. The frequency characteristic of power cable is obtained by a very powerful extrapolating approach, i.e. Cauchy method. The extrapolating results are compared with those from the frequency point-by-point matching approach. The method is very time saving because only the low rank frequency derivative information of the power cable impedance is required.
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