The article is devoted to the effects of geomagnetic-induced currents (GIC) on electrical equipment of power systems and analyzes technical measures for protection against such effects. It is noted that the difference between high-altitude nuclear detonation and solar storm GICs forces applying different methods of electrical equipment protection. It also illustrates that enhancement of transformer immunity to GICs without saturation prevention is not an effective measure to protect the power system. The article offers a special relay designed for fast disconnection of the transformer under GICs.