Occasionally plasma erupts from the surface of the sun, which, itself is a mass of moving, energy charged plasma. Solar flares, or holes in the solar corona can also lead to emissions of an energy wave. The eruption travels through space as a solar wind, and, if aligned toward the earth, the solar wind shock wave can hit the earth’s atmosphere—which has magnetic properties. The shock typically occurs 24 to 36 hours after a solar event, and magnetic storms usually last for 1 to 2 days. However, the storms can last for many days. The solar wind will have a magnetic property or bursts of energy that can, in a large geomagnetic storm, rapidly change the magnetic field around the earth’s core. This leads to induced currents of energy in long metallic conductors (wires, rails, etc.). Transformers in the grid used to step up or step down power voltages are connected to these wires, and are subject to damage in the cores where wire copper windings can melt from the induction of strong magnetic fields in the transformers due to the increased current in the wires (caused by EMP). There are around 300 key transformers that are used in the initial segments of the U.S. Electric Grid. There are few spare transformers, and the time it takes to manufacture a replacement can take more than a year under normal conditions. These units are not manufactured in the United States, making replacements difficult to obtain.