Wind turbines are located in open spaces often in rocky mountainous areas where soil resistivity is high making them particularly vulnerable to lightning currents that may threaten human life or damage expensive equipment.
In higher resistivity environments often associated with wind farm installations, similar low resistance values can be achieved by simply increasing the length of the radials. Four 75 m (246 foot) SAN-EARTH radials yield a resistance of 2.4 Ω in a 500 Ω-m resistivity environment. Installation is relatively simple. First, 0.25 m (10 inch) wide trenches are dug to an appropriate depth, one meter in the examples here. SAN-EARTH can be installed as a dry powder or mixed with water and applied as a mortar. The counterpoise wire is placed in the trench so that it is surrounded by the SAN-EARTH material. Over time SAN-EARTH hardens to become a conductive solid. Thus, the surface area of the grounding electrode is greatly increased and lower resistance values are achieved. Corrosion in the counterpoise wire is prevented and conductor theft becomes much more difficult.
Wind turbines grounded in this way can be connected together to achieve even more dramatic results. In the example below, the grounding electrode systems for three turbines are connected together using the SAN-EARTH design. Vertical ground rods, often difficult to install at wind farm locations, are not needed to achieve a consistent low resistance connection to earth.
Grounding resistance and soil resistivity are, by definition, always proportional. Knowing that, we can see that the system above would yield a resistance value of 1.32 Ω in a 1,000 Ω-m resistivity environment. Even if the resistivity went as high as 3,000 Ω-m, this design would produce a resistance value below 4 Ω.