  Wide-band cable models for the prediction of electromagnetic transients in
power systems require the accurate calculation of the cable series impedance as
function of frequency. A surface current approach was recently proposed for
systems of round solid conductors, with inclusion of skin and proximity
effects. In this paper we extend the approach to include tubular conductors,
allowing to model realistic cables with tubular sheaths, armors and pipes. We
also include the effect of a lossy ground. A noteworthy feature of the proposed
technique is the accurate prediction of proximity effects, which can be of
major importance in three-phase, pipe type, and closely-packed single-core
cables. The new approach is highly efficient compared to finite elements. In
the case of a cross-bonded cable system featuring three phase conductors and
three screens, the proposed technique computes the required 120 frequency
samples in only six seconds of CPU time.
