Lightning electromagnetic fields and their induced voltages on overhead lines: the effect of a non-flat lossy ground

2015 IEEE International Symposium on Electromagnetic Compatibility (EMC)

et al. 2015

In this paper, we analyze the propagation effects of hilly and mountainous terrain on lightning magnetic fields by using a three-dimensional (3-D) finite-difference time domain (FDTD) method. We show that the waveshape, peak value and time delay of the magnetic fields can be significantly affected when propagating along a hilly terrain. It is found in particular that the time delay of the magnetic field increases with increasing height of the mountains. The observed time delays resulting from the propagation along a hilly terrain might impact the accuracy of lightning location systems based on the time-of-arrival technique. Keywords-lightning magnetic fields; three-dimensional (3-D) finite-difference time-domain (FDTD); hilly and mountainous ground.978-1-4799-6616-5/15/$31.00 ©2015 IEEE

Section: Fdtd Simulation Results and Analysismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Propagation effects on lightning magnetic fields over hilly and mountainous terrain

Paknahad

2015 IEEE International Symposium on Electromagnetic Compatibility (EMC)

et al. 2015

“…Soto et al [23], [24] presented finite-difference time-domain (FDTD) calculations of lightning electromagnetic fields for a lightning discharge striking the top of a cone-shaped mountain. Paknahad et al [25] presented for a similar configuration, finite-element method (FEM) simulations for both aboveground and underground fields. These studies showed that lightning electromagnetic fields could be affected by a nonflat ground configuration.…”

mentioning

confidence: 99%

On Lightning Electromagnetic Field Propagation Along an Irregular Terrain

Azadifar

IEEE Trans. Electromagn. Compat.

et al. 2016

Self Cite

Abstract-In this paper, we present a theoretical analysis of the propagation effects of lightning electromagnetic fields over a mountainous terrain. The analysis is supported by experimental observations consisting of simultaneous records of lightning currents and electric fields associated with upward negative lightning flashes to the instrumented Säntis tower in Switzerland. The propagation of lightning electromagnetic fields along the mountainous region around the Säntis tower is simulated using a full-wave approach based on the finite-difference time-domain method and using the two-dimensional topographic map along the direct path between the tower and the field measurement station located at about 15 km from the tower. We show that, considering the real irregular terrain between the Säntis tower and the field measurement station, both the waveshape and amplitude of the simulated electric fields associated with return strokes and fast initial continuous current pulses are in excellent agreement with the measured waveforms. On the other hand, the assumption of a flat ground results in a significant underestimation of the peak electric field. Finally, we discuss the sensitivity of the obtained results to the assumed values for the return stroke speed and the ground conductivity, the adopted return stroke model, as well as the presence of the building on which the sensors were located.

“…The same increase can also be observed for the magnetic field for angles up to about α = 45 ° , beyond which it follows a slightly decreasing trend (see Figures e, e, and e). It is interesting to observe that a similar behavior was reported in a recent study by Paknahad et al [], in which the effect of a nonflat lossy ground on the lightning electromagnetic fields as well as the associated induced voltages on overhead lines was analyzed using a full‐wave finite element approach. Paknahad et al [] showed that the azimuthal magnetic field features a similar behavior as in our case, namely an increase with an increasing steepness of the nonflat surface up to a certain value (of about 60° or so), followed by a decreasing trend.…”

Section: Results and Analysismentioning

confidence: 99%

“…It is worth noting that our 3‐D FDTD has been tested and validated by comparing its results with those obtained using a finite element method approach, and excellent agreement has been obtained [ Li et al , ; Paknahad et al , ].…”

Section: Adopted Models and Methods For The Analysismentioning

confidence: 99%

Analysis of lightning electromagnetic field propagation in mountainous terrain and its effects on ToA‐based lightning location systems

Azadifar

et al. 2016

JGR Atmospheres

Self Cite

In this paper, we analyze the propagation effects on lightning-radiated electromagnetic fields over mountainous terrain by using a three-dimensional (3-D) finite difference time domain (FDTD) method. We also discuss the time delay error in the time-of-arrival (ToA) technique currently used to locate lightning in detection networks, specifically. Furthermore, the accuracy of different approximate methods presented in the literature is discussed and tested by using our 3-D FDTD method. It is found that (1) the time delays and amplitudes of the lightning-radiated electromagnetic fields can be significantly affected by the presence of a mountainous terrain and associated diffraction phenomena; (2) for a finitely conducting ground, the time delay shows a slight increase with the increase of the observation distance, but the time delay resulting from the finite ground conductivity appears to be smaller than that caused by the mountainous terrain; and (3) the timing error associated with the ToA technique depends on the threshold times. Threshold times of 10% and 20% of the peak provide very similar results compared to those corresponding to the peak of the first derivative of the magnetic field, and the threshold time exceeds 50% of the initial rising amplitude of the signal. Furthermore, we have assessed the accuracy of two simplified methods (terrain-envelope method and tight-terrain fit method) to account for the time delays resulting from the propagation in a mountainous terrain. It is found that both methods result in time delays that are in reasonable agreement but always overestimating the results obtained using the full-wave 3-D FDTD approach for the perfectly conducting ground. These two methods represent interesting alternatives to account for the time delay over a nonflat terrain using the terrain model.