Markus Nyffeler

Radiated Fields From Lightning Strikes to Tall Structures: Effect of Upward-Connecting Leader and Reflections at the Return Stroke Wavefront

An extension of the engineering return-stroke models for lightning strikes to tall structures that takes into account the presence of possible reflections at the return-stroke wavefront and the presence of an upward-connecting leader is presented. Based on the approach proposed by Shostak et al., closed-form, iterative solutions for the current distribution along the channel, and the strike object are derived. Simulation results for the magnetic fields are compared with experimental waveforms associated with lightning strikes to the CN Tower (553 m). It is shown that taking into account the reflections at the return-stroke wavefront results in better agreement with the fine structure of the magnetic-field waveforms. Moreover, the obtained results are in better agreement with experimental observations, reproducing both the early narrow undershoot and the far-field zero crossing. The results also suggest that the typical double-peak response of the radiated fields from tall structures might be due to the combined effect of upward-connecting leaders and reflections at the return-stroke wavefront.

Lightning electromagnetic fields at very close distances associated with lightning strikes to the Gaisberg tower

In this paper we present and discuss measurements of electric (vertical and radial) and magnetic fields from leaders and return strokes associated with lightning strikes to the 100 m tall Gaisberg tower in Austria obtained in 2007 and 2008. The fields were measured at a distance of about 20 m from the tower. Simultaneously, return stroke currents were also measured at the top of the tower. The data include, for the first time at such close distances, simultaneous records of vertical and horizontal electric fields. The vertical electric field waveforms appeared as asymmetrical V-shaped pulses. The initial, relatively slow, negative electric field change is due to the downward leader, and the following, fast, positive electric field change is due to the upward return stroke phase of the lightning discharge. The horizontal (radial) electric field due to the leader phase has a waveshape similar to that of the vertical electric field. However, the horizontal field due to the return stroke is characterized by a short negative pulse of the order of 1 mu s or so, starting with a fast negative excursion followed by a positive one. The return stroke vertical electric field changes appear to be significantly smaller than similar measurements obtained using triggered lightning. This finding confirms the shadowing effect of the tower, which results in a significant decrease of the electric field at distances of about the height of the tower or less. The vertical and horizontal E field changes due to the return stroke were also found to be larger on average than the leader electric field changes. In a significant number of cases (33%), the vertical electric field waveforms due to the return stroke were characterized by a first peak exceeding the typical late-time flattening due to the electrostatic term. This is in contrast with similar measurements related to triggered lightning which do not exhibit such a first peak. About one quarter of the measured vertical electric field waveforms (18 pulses out of 76) featured an unusual waveform characterized by a positive leader field change followed by a bipolar return stroke field change with a zero crossing time of about 60 mu s.

Experimental Characterization of the Response of an Electrical and Communication Raceway to IEMI

This paper reports the results of two experimental campaigns aimed at studying the high-frequency response of a raceway containing low voltage power, telephone, and Ethernet cables, to external electromagnetic field illumination. The raceway was tested against HPEM transients inside a gigahertz transverse electromagnetic (GTEM) cell and low-power fields inside a reverberation chamber (RC). The high-power electromagnetic (HPEM) tests revealed that the low-voltage power cables have the greatest coupling under a hyperband illumination, compared to telephone and Ethernet cables. The RC tests allowed the determination of statistical transfer functions from random incident field configurations into DM voltage in cable loads. The responses were found to be governed by the raceway under test at the lower frequencies (below 1 GHz). Between 0.2 and 1 GHz, the raceway gives about 10 dB higher coupling than a short patch cable. The difference is even greater at lower frequencies and for shielded cables. In the frequency band 1-3 GHz, little difference was observed between short patch cables and the full raceway, but both were still significantly higher than direct coupling to the measurement card. Beyond 3 GHz, the coupling is clearly dominated by the terminal equipment. The experiments performed in this paper provide a better understanding of the expected induced voltages and currents in commercial cable systems when exposed to intentional electromagnetic interference (IEMI)-like signals.

Response of canonical ports to a high power electromagnetic excitation

In this work, we present a methodology to calculate the required electromagnetic environment to achieve the maximization of the thermal response of a canonical port of interest (mainly electronic components) in order to achieve permanent damage. The |E2| τ product (E being the amplitude of the impinging electric field and τ the duration of the illumination) is shown to be the key parameter to define the required electromagnetic environment that could lead to the thermal destruction. Application examples with canonical incident waveforms are presented and discussed.

Corrections to “Study of the Propagation of Common Mode IEMI Signals Through Concrete Walls”

Presents corrections to the paper, “Study of the propagation of common mode IEMI signals through concrete walls,” (Mora, N., et al), IEEE Trans. Electromagn. Compat., vol. 60, no. 2, pp. 385–393, Apr. 2018.

Study of the Propagation of Common Mode IEMI Signals Through Concrete Walls

In this paper, a model to analyze the propagation of intentional electromagnetic interferences disturbances along penetrating conductors into concrete walls is proposed. The model is based on the transmission line theory and considers the attenuation of the signal as a function of the water content of the concrete, the thickness of the wall, and the frequency of the signal. The model is validated with experiments performed with a vector network analyzer and a time-domain reflectometer. A numerical parametric study is performed in order to quantify the expected attenuation levels of a concrete wall with different water content levels. The simulation results show that the peak amplitudes of the disturbance can be significantly attenuated for both dry and wet concrete.

Vertical and radial electric fields from leaders and return strokes associated with lightning strikes to the Gaisberg Tower

We present and discuss measurements of electric fields (vertical and radial) from leaders and return strokes associated with lightning strikes to the Austrian Gaisberg Tower (GBT) obtained in 2008. The fields were measured at a distance of about 20 m from the tower. Simultaneously with the fields, return-stroke currents were also measured at the top of the tower. The vertical electric field waveforms appeared as asymmetrical V-shaped pulses. The initial, relatively slow, negative electric field change is due to the downward leader and the ensuing fast positive field change is due to the upward return stroke phase of the lightning discharge. The horizontal (radial) electric field due to the leader phase has a similar waveshape to the vertical electric field. However, the radial field due to the return stroke is characterized by a short negative pulse of the order of 1 microsecond or so, starting with a fast negative excursion followed by a positive one.