Transient Ground Potential Rises at a nuclear fusion experimental power plant hit directly by a lightning strike

Electric substations are often exposed to lightning strikes. When that happens, very fast large transient voltage stresses occur. Surge limiters can be destroyed and electronic equipment inside control rooms can be damaged. In order to develop appropriate mitigations that prevent such catastrophic damages, a model of a lightning strike hitting a shielding structure of a substation feeding an experimental nuclear fusion facility (Tokamak) is analyzed. Transient Ground Potential Rises (TGPR) of the substation are studied using an electromagnetic field approach. The system analyzed consists of a detailed model of the grounding system of the substation as well as a skeleton of the power plant grounding system. The effects of the soil resistivity on the TGPR are studied. It is shown that the transient GPR increases when the soil resistivity increases. When the soil resistivity is low, there is little difference in the transient GPR between the substation grounding system alone and the substation grounding system interconnected to the power plant grounding system. However, when the soil resistivity is high enough, the interconnected grounding system between the substation and the power plant can significantly reduce the transient GPR in the substation control room in both its magnitude and its extent over time. Consequently, stress voltages on electronic equipment inside the substation control room can be greatly reduced.