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This paper proposes a circuit model of a lightning strike to a tall grounded object. The model can consider the direction-dependent attenuation characteristic of current propagating along with a tall grounded object as well as frequency-dependent characteristics of lightning channel and tower impedances, in contrast to the conventional lossless transmission line representations. Hence, the model removes the use of an unrealistic high grounding impedance for approximately expressing the significant current attenuation propagating upward along with the tall object. Measured lightning currents at a height of about 500 m of the 634-m-high Tokyo Skytree are accurately reproduced with the proposed model, which assumes a constant lightning channel impedance with a current source that generates a current waveform decaying with time, or a frequency (time) dependent lightning channel impedance with a step-like voltage source. The proposed model can also be used for lightning electromagnetic pulse calculations. [ABSTRACT FROM AUTHOR]

The basic and qualitative characteristics of the proximity effect in comparison with the skin effect on multiconductors are investigated based on finite-difference time-domain simulations to find equivalent/approximate geometrical parameters by which a transient can be calculated by existing electromagnetic transients-type simulation tools. The proximity effect appears very different depending on the current directions on the conductors, and is cancelled out in the center conductor on a three-conductor system. A filament current assumption results in a quite different current distribution from that considering the conductor volume. Based on the investigation and the IEC formula, an approximate formula of the conductor impedance considering the proximity and skin effects is proposed. The validity of the proposed formula is confirmed by calculated results of the impedance compared with the IEC formula, and of an intersheath mode transient in comparison with a field test result. The formula makes it possible to calculate a transient with the proximity effect by the EMTP. [ABSTRACT FROM AUTHOR]

An improved representation of a straight thin wire for a 3-D finite-difference time-domain simulation has been applied to the transient analysis of a straight thin wire in a lossy medium, and its validity has been shown. In this representation, a straight wire having a specified radius is simulated by a straight wire having the equivalent radius 0.199Δs, where Δs is the lateral side length of cubic cells employed, embedded in an artificial parallelepiped medium having modified conductivity (only if it is in a lossy medium), modified relative permittivity, and modified relative permeability. Also, the equivalent radius of a staircase-approximated oblique wire in air has been evaluated, and its thin-wire representation has been discussed. [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]

The equivalent radius of a thin wire, which is represented by forcing the tangential electric field along the wire axis to zero in a three-dimensional finite-difference time-domain simulation, has been evaluated on the basis of a surge or characteristic impedance of a perfectly conducting horizontal wire above a perfectly conducting ground. It is 0.199Δs, where Δs is the lateral side length of cubic cells employed, and is smaller than the equivalent radii, 0.230Δs and 0.208Δs, estimated by Noda and Yokoyama (2002) and by Railton et al. (2006), respectively. Further, the thin wire representation of Railton et al. with this equivalent radius, which embeds a wire having the equivalent radius in an artificial parallelepiped medium having modified relative permittivity and permeability, has been proposed, and its validity has been tested for a horizontal wire and a vertical wire. [ABSTRACT FROM PUBLISHER]

Carson's, Pollaczek's, Wise's, and Sunde's earth-return impedances of an overhead line have been examined, and errors involved in the formulas are explained. Modified Pollaczek's and Carson's/Sunde's formulas are described. Wave propagation characteristics on a multiconductor in a high-frequency region are evaluated by adopting the modified earth-return impedance and Wise's earth-return admittance. Sommerfeld–Goubau propagation in a high-frequency region, which shows transition between transverse electromagnetic and transverse magnetic propagation, has been confirmed in the calculated results which agree with those predicted by Kikuchi for a single conductor. On a multiconductor system, it is found that the aerial mode also shows Sommerfeld–Goubau propagation when the separation between conductors is large and the earth resistivity is high. [ABSTRACT FROM AUTHOR]

This paper investigates the validity and the application limit of experimental results on a scale model above a conducting plate, such as an aluminum (Al) or copper (Cu) plate, representing a real power system, which is too large for experimental measurements. The surge characteristics on a scale model of an overhead conductor above an Al plate are compared with that above a real earth. The experimental results are compared with analytical and numerical simulation results by the electromagnetic transients program and finite-difference time domain method. It is clear that the Al plate can represent the real earth only for an initial part of a surge waveform until reflection comes back from the other end of the conductor. The surge waveform on the Al plate noticeably deviates from that on the real earth as time passes. Correspondingly, the characteristic impedance of the Al plate differs from that on the real earth depending on the conductor height and the separation between the conductors. [ABSTRACT FROM AUTHOR]

This paper has investigated the nonuniform characteristics of a counterpoise based on the frequency-dependence of R, L, C, and G and propagation parameters identified from measured results of transient voltages and currents on the counter- poise. It becomes clear that the characteristic impedance is significantly length-dependent (i.e non-uniform, at a high frequency). As the frequency tends to infinity, the maximum value of the characteristic impedance is almost the same irrespective of its geometry, physical constants and soil conditions. However, the characteristic impedance at a section near to source end is far smaller than that near to the remote end. The apparent series impedance increases and the admittance decreases for a counterpoise section farther to the source end. The propagation constant shows less noticeable nonuniformity than that for the characteristic impedance. [ABSTRACT FROM AUTHOR]

This paper has derived an impedance formula for conductor's semiconducting layer based on a conventional circuit theory. The formula is confirmed to be identical to an accurate one derived by solving Maxwell's equation. A wave-propagation characteristic and a transient voltage on a cable having the semiconducting layer on the conductor's surface are evaluated by applying the derived formula, and are compared with those on a cable with no semiconducting layer. The semiconducting layer increases the conductor impedance, and thus, the attenuation constant is increased, and the propagation velocity and the characteristic impedance are decreased for a coaxial mode by the semiconducting layer, hut the inter-phase mode of propagation is not affected. A transient voltage is attenuated more and its oscillating period becomes greater than those on a cable with no semiconducting layer. The effect of the semiconducting layer impedance on the wave-propagation characteristic and the transient voltage is rather minor when the layer thickness is small and the resistivity is high, and the semiconducting layer effect is dominated by its admittance. [ABSTRACT FROM AUTHOR]

This paper has proposed an impedance formula of pipe enclosed and tunnel-installed cables of which the thickness of the pipe and tunnel wall is finite. Thus, it is composed of a two-layered conductor (i.e., the first medium is the finite thickness pipe or the finite thickness tunnel wall, and the second medium is the outer conductor to infinite). The impedance by the formula developed in the paper shows a quite different characteristic from that calculated by an existing impedance formula which was derived from the assumption of an infinitely thick pipe. Wave propagation and transient voltage characteristics are investigated using the proposed formula, and a difference from those by the existing formula is made clear. The proposed impedance formula has made it possible a detailed and more accurate analysis of wave propagation and transient overvoltage characteristics on pipe-enclosed and tunnel-installed cables. [ABSTRACT FROM AUTHOR]