Abraham Rubinstein

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.

On wire-grid representation of solid metallic surfaces

This work deals with the wire-grid representation of metallic surfaces in numerical electromagnetic modeling. We discuss in particular the adequacy of the well known and widely used equal area rule (EAR) to calculate the radii of wire-grid models. We show that the EAR is accurate as long as the wire grid consists of a simple rectangular mesh. For more complex body-fitted meshes, using other polygons such as triangles, the EAR appears to be less accurate in reproducing the electromagnetic field scattered by metallic bodies. The conclusions of the paper are supported by numerical simulations performed using a parallel version of the numerical electromagnetics code and experimental data obtained on a vehicle illuminated by an electromagnetic pulse simulator.

A parallel implementation of NEC for the analysis of large structures

We present a new, parallel version of the numerical electromagnetics code (NEC). The parallelization is based on a bidimensional block-cyclic distribution of matrices on a rectangular processor grid, assuring a theoretically optimal load balance among the processors. The code is portable to any platform supporting message passing parallel environments such as message passing interface and parallel virtual machine, where it could even be executed on heterogeneous clusters of computers running on different operating systems. The developed parallel NEC was successfully implemented on two parallel supercomputers featuring different architectures to test portability. Large structures containing up to 24000 segments, which exceeds currently available computer resources were successfully executed and timing and memory results are presented. The code is applied to analyze the penetration of electromagnetic fields inside a vehicle. The computed results are validated using other numerical methods and experimental data obtained using a simplified model of a vehicle (consisting essentially of the body shell) illuminated by an electromagnetic pulse (EMP) simulator.

Application of the Cascaded Transmission Line Theory of Paul and McKnight to the Evaluation of NEXT and FEXT in Twisted Wire Pair Bundles

The cascaded transmission line theory of Paul and McKnight is used in this paper to predict near-end crosstalk (NEXT) and far-end crosstalk (FEXT) in a bundle of twisted wire pairs. The approach is validated using the CST Cable Studio commercial software and experimental data. NEXT and FEXT along twisted pair bundles are then evaluated using a pure deterministic approach for the electromagnetic coupling while taking into account the random distribution of victim and aggressor pairs in the bundle. The results obtained using the presented approach are compared with available simplified empirical expressions (ANSI/FSAN). It is shown that the simplified expressions are able to predict the overall trend of the power sum loss. However, they do not always provide the worst case values. The presented theory can find important applications in the design of data transmission systems for which accurate crosstalk modeling is a vital task. It can be used for example as a replacement for the experiments in obtaining the parameters of simplified models for NEXT and FEXT.

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.

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.

Preliminary comparison of data from the Säntis Tower and the EUCLID lightning location system

In this paper, direct lightning current measurements obtained on the Säntis Tower from June 1st, 2010 to May 31st, 2011 are used to evaluate the ability of the EUCLID lightning detection network to detect this type of lightning triggered by a tall tower in terms of detection efficiency, location accuracy and peak current estimates. The Säntis Tower is a 124-meter tall tower sitting on the top of the Säntis Mountain (2500 m) in Switzerland. The tower has been instrumented to measure waveforms of the lightning current and of its time derivative. In the considered period, 57 flashes were recorded at the Säntis Tower out of which 15 were of positive polarity. The data have been correlated to EUCLID data by comparing the time-stamps provided by the GPS time references. The flash detection efficiency for negative flashes is estimated to be 93%. The median value of the location error is 126 m. The EUCLID peak current estimates were on average significantly larger than the measured current. The measurements include four typical positive flashes, which were successfully detected by EUCLID. The location errors for the positive events ranged from 1 to 3 km, with a median of 959 m.

A physical interpretation of the equal area rule

This paper presents a derivation and a physical interpretation of the equal area rule (EAR) for wire-grid simulation of surfaces. We propose a new procedure that leads to a formulation for obtaining the radii for an arbitrarily meshed surface. A simple comparison of the classical EAR and the new equal area rule (NEAR) is presented in which the electric field inside a closed metallic surface, which is known to be identical to zero, is calculated using the radii predicted by the two methods. The results show that the proposed new equal area rule predicts a smaller field for the frequency range considered, suggesting an improvement over the classical EAR.

A concept to enhance system data rate for PLC access networks

This paper presents an approach to divide a PCL single-master operated cell into multiple sub-cells featuring each an individual master (i.e. multi-master), in order to increase the overall system data rate. This is achieved by using blocking filters to allow frequency reutilization. Measurements were carried out in the village of Saint Sulpice, near the city of Lausanne in Switzerland, in order to verify the concept and the possible use of the blocking filters. Our results show that the radio frequency (RF) separation obtained using blocking filters is, in certain cases, effective enough to properly separate signals belonging to different low voltage (LV) feeders on the same substation. In some other cases, despite the use of properly designed and integrated blocking filters, additional mechanisms must be used. In particular, the Synchronised Tx/Rx for all masters and the Rx/Tx frequency duplexing mechanisms are discussed.

On the use of the equal area rule for the wire-grid representation of metallic surfaces

This paper presents a brief theoretical discussion on the issue of the wire-grid representation of surfaces using the numerical electromagnetics code (NEC). Different approaches for the determination of the parameters (in particular, the segment radii) of a wire-grid representation of a metallic surface are presented. These approaches are tested vs experimental data on electric field distribution inside a transverse electro-magnetic (TEM) cell. The obtained data are compared to simulation results showing reasonable agreement for models featuring rectangular meshes