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When lightning strikes a transmission tower or overhead line, the lightning current generates a spherically expanding electromagnetic field. The propagation mode of an expanding electromagnetic wave is different from that of a transverse electromagnetic (TEM) wave, which is applied to the modeling of transmission lines. This paper presents an equivalent circuit model of an overhead transmission line that considers the TEM‐mode formation delay. The TEM‐mode formation delay is approximately represented by the first‐order delay functions in surge impedances and time delays in the mutual coupling from one line to the others. The proposed circuit model of the overhead line is introduced to the Alternative Transients Program version of Electromagnetic Transients Program using the MODELS language through a formulation in the phase domain based on Dommel's method. The results of the proposed model are validated through a comparison with the results of a three‐dimensional numerical electromagnetic analysis. Furthermore, the effect of the delay of the TEM‐mode formation on the voltages across the insulator strings of a lightning‐struck tower is described by referencing a previous experimental study conducted using an actual 500 kV transmission tower. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

The electromagnetic fields, which are produced by lightning currents flowing into a transmission tower and into overhead ground wires, spherically expand with time, and propagate as non-transverse electromagnetic (TEM) waves at least within the round trip time of the traveling wave along the tower. In this paper, a distributed-parameter line model of a vertical double-circuit transmission tower with an overhead line struck by lightning is composed considering the non-TEM characteristics. The surge impedances of the tower, ground wires, and phase conductors increase with time and reach their TEM-mode or steady state values with time constants determined from the configuration. In addition, the significant wave attenuation along the tower is included in the circuit model according to the propagation characteristic determined by the tower configuration. The virtual inductive grounding impedance or damping circuits for approximately representing the wave attenuation is no longer needed. The proposed model is applied to four types of transmission towers. Waveforms of voltages across insulator strings computed by the finite-difference time-domain method, which are regarded as the reference, are well reproduced by the proposed model. Computation efficiency is drastically improved by the proposed model comparing to the numerical electromagnetic field analysis. [ABSTRACT FROM AUTHOR]

The wave propagation characteristics on an overhead conductor in a high-frequency band were investigated based on the Wise's earth-return admittance and modified Pollaczek's (accurate) earth-return impedance in a previous paper. In this paper, the characteristics are studied using the numerical electromagnetic code (NEC), which is based on the method of moments in the frequency domain. Results computed using NEC show quite similar characteristics to those described in the previous paper, i.e., a transition between transverse electromagnetic and transverse magnetic propagation called Sommerfeld–Goubau propagation. Thus, the mode transition has been confirmed. Also, observation indicates that Wise's admittance and an accurate impedance (transmission line approach) are applicable to investigating high-frequency wave propagation on an overhead horizontal conductor, as Kikuchi pointed out. [ABSTRACT FROM PUBLISHER]

SUMMARY In this paper, representations of a perfectly conducting thin wire and an imperfectly conducting medium in the transmission line modeling (TLM) calculation are briefly explained. Then, the method is applied to analyzing surge responses of a vertical parallelepiped grounding electrode and a square-loop grounding electrode. Surge responses calculated using the TLM method agree reasonably well with the corresponding responses measured and calculated using the finite-difference time-domain method. It is probably the first time that surge responses of grounding electrodes have been analyzed reasonably accurately using the TLM method. [ABSTRACT FROM AUTHOR]

In this paper, a procedure for computing transient electromagnetic fields with the constrained interpolation profile (CIP) method in the two-dimensional (2-D) cylindrical coordinate system has been derived. Then, it has been applied to analyzing electromagnetic pulses produced by a current wave propagating upward along a vertical lightning return-stroke channel. CIP-computed waveforms agree well with corresponding waveforms computed using analytical expression of Uman et al. or the finite-difference time-domain method. [ABSTRACT FROM AUTHOR]

Highlights: [•] A frequency dependent circuit model of a vertical conductor is proposed. [•] Semlyen's line model expressing the vertical conductor can be derived either from electromagnetic field analysis or measurement. [•] The method is applicable to not only a wind turbine, but also a transmission tower. [ABSTRACT FROM AUTHOR]

In this paper, a procedure for computing electromagnetic fields with the transmission-line-modeling (TLM) method in the two-dimensional (2-D) cylindrical coordinate system has been derived. Then, it has been applied to analyzing electromagnetic pulses produced by a current wave propagating upward along a vertical lightning return-stroke channel. TLM-computed waveforms agree well with corresponding waveforms computed using analytical expression of Uman et al.and the finite-difference time-domain method. [ABSTRACT FROM PUBLISHER]

This paper presents the calculation of lightning- induced voltages over lossy ground, generated by a lightning strike to a flat ground and a tall object. A hybrid electromagnetic circuit model method adopting an approximation formula, i.e., Cooray-Rubinstein expression, is employed in this paper. A comparison of the simulation results with experimental data shows that the Cooray-Rubinstein formula is still good enough for the calculation of a lightning-induced voltage. Electric fields calculated by the proposed method, and by equations derived by Master and Uman and a conventional dipole technique, are compared. The two approaches yield the same total electrical fields but different components of electrostatic, induction and radiation. [ABSTRACT FROM AUTHOR]

We have shown that finite-difference time-domain (FDTD) electromagnetic computations for a conductor system having a radius smaller than 0.15Δr or larger than 0.65Δr (Δr is the lateral side length of cells employed), modeled using arbitrary-radius-wire representations proposed so far with a time increment determined from the upper limit of Courant's stability condition, result in numerical instability. A primary factor causing this numerical instability is that the speed of waves propagating in the radial direction from the wire in the immediate vicinity of the wire exceeds the speed of light, and therefore, Courant's condition is not satisfied there. It is further shown that for these cases, the arbitrary-radius-wire representation can be improved by modifying the material parameters for the axial field components closest to the wire as well as those for the radial electric and circulating magnetic field components. The improved wire representation is effective in representing a wire whose radius ranges from 0.0001Δr to 0.9Δr. [ABSTRACT FROM AUTHOR]

Archorn voltages of a simulated 500-kV twin-circuit line, in the case of one-phase back-flashover due to lightning to a tower top, are analyzed by the thin-wire time-domain analysis (TWTDA) code. Prior to this analysis, a recently proposed fiashover model is incorporated into TWTDA. It becomes clear that the archorn voltages of the other two phases show a quite similar time-varying characteristic after one-phase back-flashover. An EMTP simulation is also carried out, The archorn voltages computed by the electromagnetic transients program (EMTP) agree well with those computed by TWTDA before the back-flashover on one phase. On the other hand, during about 1 μs after the one-phase back-flashover, the archorn voltages of the other two phases computed by EMTP deviate much from those computed by TWTDA. Particularly in the case of the middle- or the lower-phase back-flashover, the deviation is noticeable. The reason for this discrepancy is discussed. [ABSTRACT FROM AUTHOR]

• The paper evaluates insulator voltages of a vertical double-circuit transmission tower due to a lightning strike to the tip of tower top cross-arm by the finite-difference time-domain (FDTD) method. • The insulator voltages are up to 7% higher in the lightning struck-side than the other side, and this characteristic can affect the back-flashover phases. • An equivalent circuit model of a transmission tower that can consider the lightning struck point and cross-arms is proposed. • The proposed tower model is verified by reproducing experimental results performed for ultra-high voltage tower in the past and the FDTD simulation results. • The presented model enables in-depth analysis of lightning surges in transmission tower considering lightning struck point and back-flashover phases. This paper studies voltages generated across the insulators of a vertical double-circuit transmission tower due to a lightning strike to a tip of the tower top cross-arm, and presents a circuit analysis model of the tower considering the cross-arms. When lightning strikes the tip of tower top cross-arm, insulator voltages on the lightning-struck side are higher than those on the other side. This is because the electromagnetic field is more intense on the struck-side and it is weakened on the other side. The voltage difference can have an effect on the back-flashover occurrence. Most of existing equivalent circuits of transmission tower cannot consider the difference of electromagnetic field or its resultant voltages depending on the side of lightning strike. Here, a new equivalent circuit model, which can consider the difference of voltages depending on the side of lightning strike, is proposed for electromagnetic transient simulators. The validity of the proposed equivalent circuit model is confirmed by comparing waveforms of insulator voltages computed using the FDTD method in this paper and those measured on an actual ultra-high voltage transmission tower in the past. [ABSTRACT FROM AUTHOR]