Risk assessment of the impact of geomagnetic disturbances on the transmission grid in Switzerland

Strong solar storms causing geomagnetic disturbances (GMD) are capable of disrupting power grid operation through undesired electromagnetic interaction. Specifically, GMDs can generate quasi-DC geomagnetic induced currents (GIC) in transformer neutral windings which saturate the iron cores and lead to increased excitation current and reactive power demand: if this phenomenon is sufficiently strong and widespread it will cause a generalized decrease in bus voltages, a diminishment of the voltage stability margin and, in the worst case, a system blackout. This paper gives a brief overview of the GMD physical process and its influence on power systems and performs an explicit numerical assessment of potential GIC values and of their impact on the grid for the Swiss Transmission Network.