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Wind Turbine Tower Footing Resistance

Wind Turbine Tower Footing Resistance

Wind Turbine Tower Footing Resistance

(OP)
Hi all,

I've searched through this forum and found that other engineers faced this type of problem but I couldn't find a solution to this specific one:

I need to estimate wind turbine tower footing resistance for the purpose of lightning protection. The tower sits on a concrete foundation embedded in 10000 Ohm-m rock. For my resistance calculations I'm using Ground Mat software which doesn't take the concrete into account. Given that concrete/rebar offers low resistance path for a lightning stroke current I'd like to be able to include it somehow in my calculations. Any suggestions? Thanks in advance.   

PS The required footing resistance is 10 Ohms, so far I've been able to bring it down to 120 Ohms with 4 40m radial conductors buried at 1m depth.  

RE: Wind Turbine Tower Footing Resistance

My reference books are not with me, so verify my suggestions.

Assume the concrete foundation resitivity is = to the soil resitivity and analyze the rebar cage as an interconnected grid, if your software will do 3D modeling.

Or, assume that the concrete foundation is one large ground rod 6 meters in diameter or whatever your foundation size is.  That would be the lowest value it could achive.

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