Geomagnetic disturbances (GMDs) on the Earth originate at the Sun and can cause many different impacts on critical systems including power grids, metallic communications systems, railways, and pipelines, among others • The focus in this study was on high-voltage power systems, which are defined by the IEC as transmission grids operating at voltages above 100 kV (and usually at much higher voltages) • The emphasis on high voltage is because at the present time most of the power delivered to end users is concentrated in the delivery system from large power plants to the cities where the power is used • In order to understand the effect of GMDs on the power system, we need to understand the basic types of geomagnetic storms, the B-fields they create and how they may affect the power system