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WG B2.56 Ground Potential Rise at Overhead AC Transmission Line Structures during Faults

When a line to ground fault occurs on an AC transmission line, the ground fault current will flow through many conductive paths. One of the typical paths of the current flow is to or from the ground/earth. This generates potential on the line structure and voltage gradients on the surface of the ground around the structure.

The ground surface voltage gradients and the magnitudes of potential rises on the line structure and any metallic objects bonded to or close to the structure will depend on: structure location relative to the ground fault, fault current magnitude, phase conductor to overhead ground conductor coupling, and soil resistivity.

The grounding system design for the line structure and any installations bonded to the line structure or in close proximity is (a) to provide a means to dissipate fault currents into the ground/earth without causing damage to the facilities; (b) to protect personnel in the vicinity of grounded facilities from the hazard of electrical shock.