P. Zweiacker

Indoor radiated emission associated with power line communication systems

Experimental data characterizing indoor electric and magnetic fields radiated by power line communication (PLC) systems and used for the calculation of a local transfer function (coupling factor) are presented. It is shown that the indirect determination of electric field using magnetic field measurements and assuming a plane wave approximation may result in an underestimation of the electric field. Additionally, it is shown that the radiated field magnitudes vary significantly as a function of the position of the observation point and of the network load. A first evaluation of the indoor electromagnetic field radiated by PLC systems using NEC2 is presented and compared with experimental data.

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.

Measurement of Lightning Currents Using a Combination of Rogowski Coils and B-Dot Sensors

The paper presents laboratory tests and a characterization of commercial Rogowski coils and a specially designed B-dot sensor for the measurement of lightning currents on the Säntis telecommunications tower in Switzerland. In order to overcome the limited high frequency response of the Rogowski coils, we propose to use magnetic loops located very close to the tower. We introduce the design of a B-dot sensor based on improvements proposed by C. E. Baum, the inductance of which is lowered by extending the vertical dimension of the loop, with the overall effect of extending the operating frequency range. To overcome the integrating behavior of the loop when connected to low-impedance loads (such as 50 Ohm), an arrangement of 100-Ohm-impedance cables connected across conical-transmission-line gaps is used. The designed sensor is characterized by an upper frequency cutoff of 20 MHz and a 50 Ohm matched termination. Laboratory tests carried out in the high voltage laboratory of the EPFL show the effectiveness of the simultaneous use of Rogowski coils and B-dot sensors for the measurement of lightning currents.

Effect of Nearby Buildings on Electromagnetic Fields from Lightning

We present a discussion on the effect of nearby buildings on the electric and magnetic fields radiated by lightning. Electric and magnetic fields radiated from distant natural lightning have been measured simultaneously on the roof of a building (the Power Systems Laboratory of the Swiss Federal Institute of Technology, Lausanne, Switzerland) and on the ground at different distances away from it. The results suggest that the measured electric field on the roof of the 9-m tall building is enhanced by a factor of 1.7 to 1.9, whereas the electric fields on the ground experience a significant reduction due to the shadowing effect of the building. Also, it is shown that for a sensor located on the ground, close to a building, the magnetic field component perpendicular to the building can also experience a significant attenuation, presumably due to the effect of the induced currents in the building. The results are supported by numerical simulations, obtained using NEC-4, in which the building is represented using a simple wire-grid model.

Measurement of lightning currents using a combination of Rogowski coils and B-dot sensors

The paper presents laboratory tests and a characterization of commercial Rogowski coils and a specially designed B-dot sensor for the measurement of lightning currents on the Santis telecommunications tower in Switzerland. In order to overcome the limited high frequency response of the Rogowski coils, we propose to use magnetic loops located very close to the tower. We introduce the design of a B-dot sensor based on improvements proposed by C. E. Baum, the inductance of which is lowered by extending the vertical dimension of the loop, with the overall effect of extending the operating frequency range. To overcome the integrating behavior of the loop when connected to low-impedance loads (such as 50 Ohm), an arrangement of 100-Ohm-impedance cables connected across conical-transmission-line gaps is used. The designed sensor is characterized by an upper frequency cutoff of 20 MHz and a 50 Ohm matched termination. Laboratory tests carried out in the high voltage laboratory of the EPFL show the effectiveness of the simultaneous use of Rogowski coils and B-dot sensors for the measurement of lightning currents.

Distortion of Electric and Magnetic Fields from Lightning Due to Close-By Metallic Structures

We present experimental waveforms radiated from distant natural lightning recorded during Summer 2006. Electric and magnetic field waveforms have been measured simultaneously on the roof of a building (the Power Systems Laboratory of the Swiss Federal Institute of Technology, Lausanne, Switzerland) and on the ground 2 metres away from it. The fields have been recorded using flat plate antennas (for the E-field) and magnetic loops (for the H-field). The results suggest that the measured electric field on the roof of the building could be enhanced by a factor of 1.7 to 1.9, whereas the electric fields on the ground experience a significant reduction by a factor ranging from 5 to 20. Also, it is shown that for a sensor located on the ground close to a building, the magnetic field component perpendicular to the building can also experience a significant attenuation, presumably due to the effect of the induced currents in the building.

Current waveforms associated with positive flashes recorded on the säntis tower in summer 2010

We present in this paper measured current waveforms associated with positive flashes recorded on the Säntis tower, Switzerland, in Summer 2010. About 20% of the recorded flashes were of positive polarity (transported positive charge to ground), all of them being recorded in July and August. This percentage is considerably larger than the values observed in other studies in summer months (3% to 6.5%). The observed current waveforms can be classified into two types. The first type is characterized by three stages: (1) an initial, slowly rising portion lasting a few milliseconds, (2) the main pulse, and (3) a long continuing current that may contain several pulses of both polarities characteristic of M components. The second type of observed positive flashes is characterized by (i) the absence of any initial slowly rising portion, (ii) lower peak currents, and (iii) presence of successive pulses which may be due to an upward stepped leader. The time-derivatives of the current pulses associated with upward stepped leaders are found to be much larger than those of the main pulse. All the observed flashes contained a single main pulse, except for one flash of the second type, which featured two pulses. Our recorded data constitute the first directly-measured evidence of M-components of both polarities during a continuing current lowering positive charge to ground.

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.