To ensure a safe power system which operates correctly, a proper grounding system is necessary to provide connections to the ground at specific points. A grounding system is generally designed: (1) to reduce voltages occurring in the grounding system for short circuit situations (at power frequency) to an acceptable level in terms of step and touch voltages and to prevent damage to systems, (2) to provide good connection and a conducting path for the lightning protection system to function correctly and (3) for Electro- Magnetic Compatibility (EMC) based on generic rules to reduce the risk of damage and
interference of systems.

More specifically, the grounding system is crucial for the good protection of the primary components (mainly the power transformer) against overvoltages caused by lightning strikes, usually with the aid of surge arresters. For the Dutch power system, the grounding system has until now been represented as a simple resistance to ground for transient studies. However, literature suggests that this fails to take into account the properties of a grounding system and that their transient behaviour should be studied more extensively.

The lightning response of grounding grids can be assessed by means of simulations and by experimentation results. To performsuch studies, TenneT has different software tools available. By using the XGSLab software tool, the behaviour of grounding systems was studied. Thereafter, its transient behaviour was examined using the EMTP/ATP software tool. Using this software, a range of different simulations were conducted, such as: simple grounding conductors, a grounding system of high voltage towers and, finally, an existing substation model.