Geomagnetically Induced Currents In The Swiss Transmission Network
Strong solar storms causing geomagnetic disturbances (GMD) are capable of disrupting power grid operation through electromagnetic interaction. Specifically, GMDs can induce quasi-DC currents in the neutral windings of transformers that 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.
One notable occurrence of such an event took place in North America in March 1989, when the Hydro Quebec system was brought to collapse, leaving more than six million people without power for nine hours. Although such phenomena are in general more pronounced for high latitudes,
it cannot always be excluded a priori that similar events might not take place for example in continental Europe. Understanding, evaluating and if necessary mitigating the effects of GMD on bulk power systems is therefore important for improving overall system reliability.
The work performed in the framework of the project reviews the GMD physical process and its influence on power systems, describes some notable occurrences of related events worldwide, illustrates the countermeasures which have been formulated based on utilities’ industrial experience and assesses the effects that such phenomena could have on the Swiss Transmission Network. For the latter it is found that the risk posed by GMDs is low since their associated intensity is relatively contained and would thus not impair overall system operation.
The specific case of the Swiss Transmission Network was explicitly considered and numerically evaluated based on available data and employing techniques from the academic and industrial literature. On the basis of the conducted analysis it is reasonable to conclude that the overall risk posed by geomagnetic disturbances is low, since geomagnetically induced currents are seen to generate an additional reactive power demand (due to transformer saturation) that leads to a moderate decrease in bus voltages but that can be altogether sustained by the grid without system violations even for strong disturbances.