A Stable Extended FDTD Thin-Wire Model for Lossy Wire Structures With Irregular Cross Sections

A stable extended FDTD thin-wire model for lossy wire structures with irregular cross sections is presented for lightning transient analysis. In this model, the electro-magnetic field in the vicinity of a conductor with an irregular cross section is taken into account by adopting a single constant correction factor, and the conductor loss is represented with an internal impedance. These two parameters are calculated with a charge simulation method and an equivalent circuit method, respectively. The proposed model is validated in terms of the characteristic impedance, conductor loss and time-domain waveform with analytical and numerical methods. Good agreements are observed. Considering the rigid conductor-size/cell-size requirement and eight tedious convolutional processes in the existing non-circular thin-wire model, the implementation complexity of this proposed model is significantly simplified, and the computational stability is remarkably enhanced. Without reducing the time step, the simulation can maintain its stability when the conductor size varies from 0.01 to 1 of the FDTD cell size. It is also revealed that using a single intrinsic model for conductors with different cross sections could lead to significant calculation errors. Finally, this proposed model is applied for the lightning transient analysis in an electrified railway system.