Читать книгу Electrical Safety Engineering of Renewable Energy Systems - Rodolfo Araneo - Страница 21

The electric field is a long-range field and is zero only at infinite distance from its source, and so is the ground potential. In engineering practice, however, the design of ground electrodes is based on the area of influence, which defines the zone beyond which the ground potential can be considered negligible. If we evaluate the ground potential at the distance r = 5r0 , we obtain:

(1.12)

At a distance 5r₀ from the center of the hemisphere, the ground potential reduces to 20% of the ground potential rise, and this result has a general validity, independently of the shape of the electrode. It can conventionally be assumed that the hemispherical volume of the earth of radius 5r₀ is the area of influence of the electrode. For differently-shaped electrodes (e.g., rods, rings, grids, etc.), their maximum dimensions can be used in lieu of the radius; for instance, for grounding grids, the largest diagonal can be employed to identify the area of influence.

Two unconnected ground-electrodes are defined as independent from each other if they are outside of their respective areas of influence.