Yasuji Hongo

Lightning-induced voltage on an overhead wire dependent on ground conductivity

Lightning-induced voltage waveforms on an overhead wire are analyzed by solving the Telegraphers equation, in combination with numerical calculations of electric fields from return stroke currents as inducing sources. Based on an equivalent circuit newly developed for an explanation of this method, the roles of the vertical and horizontal electric fields in generating the induced voltage are studied, respectively. By numerical calculations, it is pointed out that the crest value of the lightning-induced voltage waveform at the end of the line is greatly affected by the ground conductivity and the lightning striking points. The accuracy of the computed results is ensured by comparison with the experimental results obtained from a geometrical model on a finitely conducting ground. >

Experimental study of lightning-induced voltage on an overhead wire over lossy ground

Experiments on the lightning-induced voltage on an overhead wire with a simulated lightning channel and a 1/20 reduced-scale model have been carried out on a lossy ground. This method is quite useful in testing various coupling models as repeated measurement along with a simple simulated lightning channel is possible. The electrical characteristics of the ground, indispensable in the calculation of the induced voltage over lossy ground, are evaluated through the comparison of the measured and the calculated horizontal electric field waveforms. The coupling model adopted in the numerical calculation of the induced voltage, including the terminations of a finite line, is verified by the good agreement of the measured and the calculated voltage waveforms. This result also verifies the usefulness of the measurement of the horizontal electric field waveform in assessing the ground conductivity in the frequency range of interest.

Induced voltage on an overhead wire associated with inclined return-stroke channel-model experiment on finitely conductive ground

Experiments on the lightning-induced voltage waveforms on an overhead wire influenced by an inclined return-stroke channel are carried out outdoors with a reduced-scale model. The measured voltages are compared with those calculated by solving the Telegraphers equation in combination with numerical calculation of electric fields associated with return-stroke currents, and the validity of the calculations is verified. The effect of the ground conductivity on the lightning-induced voltage waveform is studied based on numerical calculations and is found to be dependent on the position of the return-stroke channel relative to the overhead wire. When a return stroke hits the ground close to the end of the overhead wire, the influence of the ground conductivity on the induced voltage waveform is significant irrespective of the inclination or the direction of the lightning channel. The degree of the influence is dependent on the inclination and the direction of the channel when a return stroke hits the ground on the side of the overhead wire.

Flashover Rate of Distribution Line Due to Indirect Negative Lightning Return Strokes

The flashover rate of a distribution line associated with indirect lightning flashes is investigated based on numerical calculations and statistical analysis by taking account of the correlation between the peak value and the front duration of negative return-stroke current waveforms. When the grounding interval of an overhead ground wire and/or surge arresters is 200 m, surge arresters are more effective than an overhead ground wire in suppressing flashover of the power lines, and installation of both is very effective. The flashover rate decreases if there is correlation between the peak and the front duration of lightning current; and it significantly decreases with the increase of the ground conductivity. When the line is equipped with surge arresters only, the flashover rate associated with subsequent strokes is higher than that associated with first strokes; and calculation with the fixed front duration of 2 mus for first stroke current does not always result in good estimates of flashover rate.

Flashover Rate of 6.6-kV Distribution Line Due to Direct Negative Lightning Return Strokes

The overvoltage associated with direct lightning hits has been the important factor for the insulation design of a 6.6-kV distribution line in Japan. In this paper, the flashover rate of the distribution line associated with direct lightning hits is investigated based on numerical calculations and statistical analysis by taking into account the correlation between the peak and the front duration of negative return-stroke current waveforms. When the line is equipped with surge arresters at the interval of 100 or 200 m in addition to the overhead ground wire, the flashover rate associated with subsequent strokes is higher than that associated with first strokes. This demonstrates the importance of the study of current parameters for subsequent strokes. To obtain a conservative estimate of the flashover rate of a line with surge arresters installed every 100 m, calculated for the variable front duration, it is necessary to assume a constant front duration of less than 4 μs and 0.9 μs in the cases of first and subsequent strokes, respectively. With the increase of the installing interval of surge arresters, a constant front duration, leading to a conservative estimate, increases.

Observation of lightning performance on distribution line by still cameras

The lightning faults of power distribution lines are caused by nearby lightning stroke and direct lightning stroke and so on [1]. In order to obtain better lightning protection measures for distribution lines, it is important to clarify the causes of the lightning damages. As observations of appearance of lightning stroke on distribution lines have been made using still cameras since May 1999, we report the results of photographs of lightning strokes on and near a middle-voltage power distribution line, and side flashes on the distribution line.

Lightning-Induced Voltage on an Overhead Wire Influenced by a Branch Line

This paper explains the physical mechanism of the light flicker caused by magnetically ballasted fluorescent lamps. It is shown that the major cause of light flicker is due to voltage fluctuations or voltage waveform variations that cause the jitter of the ignition angle y, Figure 1. Fluctuations of the angle yare produced if the voltage waveform is changed from one half-cycle to the next. If the voltage spectrum contains only integer order harmonics, the waveform remains unchanged for every cycle. If the voltage spectrum contains also one or more noninteger harmonics, the waveform will vary from one cycle to the next causing “y-jitter”. A simple fluorescent lamp model, that considers the arc v& characteristic, Figure la, enabled the prediction of the time variations of the lamp voltage and current, Figure lb, as well as the arc instantaneous power, Figure IC. The computation of the mean values of the arc power for each half-cycle enabled the estimation of the “arc-power-flicker”, more correctly the relative electric arc powerThe lightning-induced voltage waveform on an overhead wire having a branch is studied based on numerical calculations. The induced voltage is calculated by the method where the tangential component of the electric field to the overhead wire is looked upon as inducing sources. Accuracy of the calculated result is ensured with experimental results obtained by using a reduced-scale model. The induced voltage on an overhead wire turns out to be influenced by its branch, and is found to be dependent not only on the configuration of a branch line but also on the location of the lightning striking point. In most of the cases, the induced voltage increases when a branch is connected to an overhead wire.

Comparison of Tohoku LLS data and lightning current waveforms in winter

Performance of a lightning location system covering Tohoku region in Japan was validated by comparing the location data and lightning current waveforms observed around a coastal area of the Sea of Japan in 2012 winter. The current waveforms were composed of continuing currents, often superimposed with isolated narrow pulse currents, and pulses. The LLS detected electric field pulses associated with the isolated narrow pulse currents and accurately located their sources, but provided no information on the continuing currents. Peak amplitudes of the isolated narrow pulse currents were slightly underestimated. For current pulses associated with negative ground-to-cloud lightning events, the peak amplitudes were overestimated several times as much as the actual values.

Flashover rate of distribution line due to indirect negative lightning return strokes

The flashover rate of a distribution line associated with indirect lightning flashes is investigated based on numerical calculations and statistical analysis by taking account of the correlation between the peak value and the front duration of negative return-stroke current waveforms. When the grounding interval of an overhead ground wire and/or surge arresters is 200 m, surge arresters are more effective than an overhead ground wire in suppressing flashover of the power lines, and installation of both is very effective. The flashover rate decreases if there is correlation between the peak and the front duration of lightning current; and it significantly decreases with the increase of the ground conductivity. When the line is equipped with surge arresters only, the flashover rate associated with subsequent strokes is higher than that associated with first strokes; and calculation with the fixed front du-ration of 2 μs for first stroke current does not always result in good estimates of flashover rate.

Role of an overhead ground wire in the generation of lightning‐induced voltage over lossy ground

The role of an overhead ground wire on the generation for lightning-induced voltage on a multiconductor line associated with a vertical return-stroke channel is studied based on numerical calculation. The induced voltage is calculated by a method in which the tangential component of the electric field to the wire is looked upon as an inducing source. The analyzed multiconductor line consists of three phase wires and an overhead ground wire having one or two earthing points. The influence of the overhead ground wire on the induced voltage is dependent on the direction of a return stroke, as well as the ground conductivity. When a return stroke is on the side of a power distribution line, the induced voltage decreases with a decrease in the earthing resistance of the overhead ground wire, irrespective of the ground conductivity. When a return stroke is close to an end of a distribution line, the influence of the overhead ground wire is dependent on the ground conductivity. In this case, the voltage induced on overhead wires over lossy ground sometimes increases with the presence of an overhead ground wire having only one earthing point. This effect can be avoided by adding earthing points to the overhead ground wire.