Return-stroke Current Parameters Research Articles

Estimation of Sparkover Rate of Medium-Voltage Line Due to Indirect Lightning Hit Taking Account of Correlation between Peak Value and Front Duration of Return-Stroke Current Waveform

The lightning-induced voltage has been one of the factors for the insulation design of a power distribution line. The authors have developed a method of analysis of induced voltages where the Agrawal's model is adopted as a field-to-line coupling model. In this paper, the sparkover rate of a medium-voltage line associated with indirect hits is investigated based on numerical calculations and statistical analysis by taking account of the correlation between the peak value and the front duration of the return-stroke current waveform. Regardless of the intensity of the correlation between these parameters, the sparkover rate associated with a subsequent stroke is higher than that associated with a first stroke when the line is equipped with surge arresters. Furthermore, it is shown that the sparkover rate significantly decreases with the increase of the correlation coefficient. This demonstrates the importance of the study of the correlation between the return-stroke current parameters.

Estimation of peak return stroke currents, current time derivatives and return stroke velocities from measured fields

Eighteen subsequent return stroke fields from triggered lightning flashes, observed at 5.16 km were used to test the ability of a return stroke model to predict the return stroke peak currents, peak current time derivatives and return stroke velocities from the measured fields. In each example, the parameters of this previously published model were changed until a best fit was obtained for the first few microseconds of the measured field and the final static field change. Once a best fit had been obtained, the corresponding peak current, the peak current time derivative and the return stroke velocity were all compared with the measured values. The mean percentage error (MPE) and the mean absolute percentage error (MAPE) of the predicted current peaks are 6.9 and 11.3%, respectively. The MPE and MAPE corresponding to the predicted current time derivatives are 13.0 and 13.8%, respectively. The model predicted velocities of these eighteen strokes had a MPE of 19.6% and a MAPE of 20.3%. The results show that the method outlined in this paper can be used to extract the return stroke current parameters from the measured electromagnetic fields.

A model for negative first return strokes in lightning flashes

A model is introduced to describe negative first return strokes in lightning ground flashes. The basic assumptions made are similar to those used previously to describe the subsequent return strokes. The model predictions are in general agreement with experimental observation. The model predicts the relationships between (a) peak current and the peak electric radiation field and (b) the peak derivatives of current and electric radiation field. These relationships can be used in the remote sensing of first return stroke current parameters through the measured radiation fields.

The effects of variation of current amplitude, current risetime, and return stroke velocity along the return stroke channel on the electromagnetic fields generated by return strokes

Calculations are presented to show how the return stroke electromagnetic fields are influenced by the variation of amplitude of the current waveform, the variation of risetime of the current waveform, and the variation of return stroke velocity along the return stroke channel. Calculations clearly show that these parameters play a dominant role in determining the characteristics of the return stroke electromagnetic fields. The narrow initial peak observed in first and subsequent stroke electromagnetic fields can be produced either by a narrow initial peak present in the current waveform, a rapid decrease in the return stroke current amplitude during the first hundred meters, a rapid decrease in the velocity of the return stroke over the first few hundred meters, or the variation of return stroke current risetime with height. The subsequent peak often observed in return stroke radiation fields can be generated either by a similar feature in the return stroke current waveform or by the variation of return stroke current risetime with height. The rate of decay of the radiation field after the initial peak depends on the rate of decay of the current waveform after the initial peak, the variation of the amplitude of the current waveform with height, and the variation of return stroke velocity with height. Calculations are also presented to show how the risetime of the current waveform affects the radiation field generated by a tortuous return stroke channel. These calculations provide an explanation for the lack of fine structure in the subsequent return stroke radiation fields though the subsequent return stroke channel is tortuous. The calculations presented in this paper demonstrate the importance of including the variation of return stroke current amplitude, variation of return stroke velocity with height, and variation of risetime of the current waveform with height in the return stroke models which are used to derive the return stroke current parameters from the return stroke electromagnetic fields.

Effects of propagation on the rise times and the initial peaks of radiation fields from return strokes

The theoretical solution to the problem of radiation from a pulsed vertical dipole over a flat homogeneous earth is employed to study the changes in rise times and the attenuation of the initial peaks of the radiation fields from lightning constructed according to the most recent experimental data on lightning return stroke radiation fields. Expected changes in rise times and the attenuation of the initial peaks for different values of distances and conductivities are presented. It is shown that for a given initial rise time there is a spread in distant rise times due to the variability of the shapes of the radiation fields. The expected spread in distant rise times for different values of distances and conductivities is calculated. The results show the importance of taking into account the propagation effects in any attempt to estimate return stroke current parameters such as rise time, rate of rise, and peak current from radiation fields which propagated over land. The predictions are compared with the available experimental data, and a good agreement is found between them.