In electrical engineering, Earth Potential Rise (EPR), also known as Ground Potential Rise (GPR) refers to the phenomenon of large current flow to the earth through earth grid impedance. The potential relative to a distant point on earth declines with distance from the source and is the highest at the point where the current enters the ground. GPR is a cause of major concern in designing of electrical substations because a high potential may be quite hazardous for the workmen and the equipment. The potential gradient (drop of voltage with distance) may be high enough that it may develop even between the workman’s two legs, or between the ground on which he is standing and a nearby metal object. Any conducting object which is connected with the earth or ground of the substation such as telephone wires, metal piping or fences may be energized even at the ground potential of the substation. This transferred potential is a great hazard to the people and equipment within and outside of the substation.
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