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.