Ground Potential Rise, or GPR, is a phenomenon that occurs when large amounts of electricity enters the earth at a given point, such as in the case of a lightning strike and/or a fault occurring at a substation or transmission tower. It is often easiest to think of a lightning strike hitting an open field. At the point where the lightning strikes, the earth itself becomes charged with electricity, of which the current moves away from the strike point and out to the surrounding soil; similar to the way a pebble makes waves when it is dropped into a pond of water. The closer to the lightning strike point, the greater the voltage.
The Ground Potential Rise issue is particularly important to copper telecommunication lines, as one can easily imagine the higher voltage at a strike/fault location can cause excess currents to travel down the copper wires to the switching station, resulting in serious damage. This is why special precautions are required under IEEE 1590 for telecommunication services in high-voltage environments such as telecommunications substations.
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The E&S Grounding Solutions Engineering Team