Abstract. Severe collapses caused by anomalies in the Earth's magnetosphere, known as geomagnetic storms, have been reported in the operation of transmission power systems. A semi-saturating phenomenon occurs in which geomagnetic induced currents (GIC) are induced in high voltage lines, which cause the power transformers of the system to be overloaded with current and subsequently also thermally. The presented article describes a device that will either completely eliminate or at least significantly reduce the possibility of a power transformer accident. The essence of this device are frequency filters, which are automatically connected in parallel to the high-voltage windings of the power transformers at the beginning of the magnetic storm and are disconnected after the storm subsides. The online information about the effect of the magnetic storm on the system is provided by the indicator to the control workplace. The proposed equipment can be easily implemented into existing transmission systems.