A 3-D FDTD Thin-Wire Model of Single-Core Coaxial Cables With Multiple Conductive Layers

In this article, a thin-wire model of single-core coaxial cables with three or more conductive layers is proposed for transient analysis using the finite-difference time-domain (FDTD) method. The multilayer cable is regarded as a series of 2-conductor coaxial transmission lines. The currents in these lines can be, however, unbalanced, and may not return via earth, such as in the case of a direct lightning strike. The FDTD method is employed to evaluate electromagnetic coupling outside the cable. Frequency-dependent surface impedances of conductors are fully considered using the Bessel functions. They are integrated into the time-domain analysis with a vector fitting technique. Updating equations for both lossless and lossy cables are derived. The proposed model is validated transmission line theory analytically and with the traditional FDTD method numerically. Good agreements are observed. Finally, the proposed model is applied to analyze the transients in a cable connection station under a direct lightning strike.