EMC aspects of a lightning surge generator and its measuring system

Adequate EMC techniques can make digital measurements in high voltage engineering as straightforward as they are in low-voltage electronics. The authors demonstrate that for the case of a 2.4 MV lightning surge generator. Interference currents in grounding structures and coaxial cables have been measured. With an EMC cabinet and a differentiating/integrating measuring system, the effects of these interference currents can be suppressed far enough to obtain clean results of the high voltage waveform on a digital oscilloscop

Common-mode currents and printed circuit boards

Common-mode (CM) currents through cables attached to printed circuit boards (PCB's) are often the main cause of interference and may even dominate the direct radiation of the board. In this paper, the authors predict the coupling between the differential-mode (DM) circuit on the board and the CM circuit in a Bersier setup, by means of a rapid transmission-line model. This coupling is expressed as the ratio of the CM current and the DM current. Several boards with different complexity were studied in the frequency domain. For demonstration purposes a board with modern digital electronics was developed. Measurements between 100 kHz-1 GHz agree with the TL model

Grounding philosophy

Two aspects of commonly used definitions of the ideal ground are inconsistent with Maxwell's laws. First, a ground cannot be a "perfect sink or source for currents"; not even the large capacitance of our globe acts as a sink. Secondly, a "perfect equipotential point or plane" can be a reality for small dc currents only. For alternating currents however, distributed magnetic fluxes near ground leads make the potential concept, as used in Kirchhoff's laws, meaningless. In this situation where network theory fails, we should concentrate on the ground currents and on the circuits in which these currents flow. Examples are given how these current loops should be designed to minimize impedance and interference. A proper design leads to compact and local grounding and to much reduced currents flowing to Mother Earth