Grounding measurements in urban areas - comparison of low and high voltage measurements in common grounding systems

Common grounding systems (global earthing systems) are not very clearly defined in standards. One definition of a common grounding system is that no dangerous touch voltages caused by ground fault currents occur. This means that a common grounding system does not depend only on the grounding system itself but also on the type and operation of the electrical grid and the protection schemes. In a resonant grounded network only low ground fault currents appear because of the compensation, therefore it is difficult to detect and clear single ground faults if desired or necessary. To provide a reliable localization of a ground fault a higher current can be injected intentionally but it must be proved that no dangerous touch and step voltages occur. To prove this in a typical urban grid, different measurements were carried out. Measurements at low and high current levels and an additional simulation are compared and discussed.