A Technique for Representing Lossy Thin Wires and Coaxial Cables for FDTD-Based Surge Simulations

To protect power equipment and electronic devices in low-voltage control circuits in power plants and substations from abnormal voltages such as lightning or switching surges, it is necessary to design effective protection measures based on the prediction of surge phenomena. Nowadays, full-wave numerical approaches have become effective tools for analyzing electromagnetic transient phenomena in three-dimensional or grounding structures. To apply the finite-difference time-domain (FDTD) method to surge analysis, several techniques for representing thin wires and coaxial cables have been developed. In this study, to simulate lossy wires and cables in FDTD-based surge simulations, first, we propose a technique for taking into account the effect of the conductor internal impedances of thin wires and metal sheath of coaxial cables by using a series of lumped-parameter frequency-dependent impedances on the conductors. Second, we propose a technique for simulating the effect of the surface transfer impedances of coaxial cables in the FDTD method while representing the metal sheath directly by a lossy thin wire in the FDTD method and solving surge phenomena inside the coaxial cables on the basis of transmission line theory. The proposed techniques are validated by circuit-theory-based simulations.