Instrumentation of the Säntis Tower for Lightning Current Measurement

In this thesis, a new experimental station was designed and built for the measurement of lightning currents. The station (Säntis Tower) was instrumented using advanced and modern equipment with remote monitoring for an accurate measurement of lightning current parameters. In Chapter 2, we present the phenomenology and classification of lightning discharges. An overview of different types of discharges is given and their typical signatures in terms of current waveform were described. Lightning current measurements obtained using different techniques are also summarized. It is emphasized that, despite the important effort in obtaining experimental data on lightning currents using different techniques, the number of available data is still limited and more data are needed to better understand the physics of lightning and to better characterize the lightning current parameters associated with different types of cloud-to-ground lightning discharges. Chapter 3 presents the characteristics of a system suitably developed to measure lightning current waveforms on the Säntis Tower in Switzerland. The system was designed considering the EMC constraints, using fiber optics as backbone for transmission of the measured signals and paying special attention to the design of the cabling, measurement boxes, protection systems and shielding. In addition, due to the harsh conditions inside the tower, where the temperature ranges from -15°C to +35°C, a system comprising a heater, a ventilator, moisture exhaust holes, and a thermal insulation material was designed to keep the temperature within acceptable limits for the components and to avoid condensation inside the PCB cards. In order to overcome the limited high frequency response of the Rogowski coils, we propose to combine them with an improved design of a B-dot sensor which does not have the shortcomings of conventional loops. 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 joint use of Rogowski coils and B-Dot sensors for the measurement of lightning currents. The measurement system allows an over-the-Internet remote maintenance, monitoring and control overall system. In particular, the status of each pair of sensors is monitored and controlled by means of a system designed, and built, using National Instruments Compact- RIO modules linked via 100Base-FX Ethernet, which uses fiber optics as a transmission medium. A data analysis software (SENDIS) was developed to analyze the obtained data, to extract statistical parameters and to allow the remote monitoring, control and programming of the different components. Algorithms implemented in SENDIS allow the detection of current components (return stroke, M-component, continuous and continuing currents) within each flash and the automatic extraction of statistical parameters of the current. In Chapter 4, w