Grounding grids

The larger the grounded grid area, the lower will be the grid resistance, and the lower the GPR and the mesh voltage. 

Figure 22.15 Area of a grounding grid and length of buried conductors...

Ft there are /t number of conductors lengthwise and /t(, widthwise and = ntimber of grounding rods used in a grounding grid at a depth of h, then the total length of the buried conductors... 

The use of salts such as magnesium, copper sulphate or calcium chloride in the vicinity of the ground grid may improve the conductivity of the soil. 

This may be substituted with the estimated maximum ground grid current, /q (Section 22.9.6), that may occur during the life of the grounding station thermal capacity factor from Table 22.5, in J/cmV°C. This is derived from formula (4,184) p), Ps in Ws/cm V °C (for details refer to lEEE-80)... 

K. K , = geometrical factors, depending upon the more important parameters such as area of the grounding grid, its depth and conductor spacing and less important factors, such as diameter of the conductors and the thickness of the finishing surface by concrete or gravel. 

This is the parameter that will help to decide the size and type of the grounding grid and design of the mesh. 

Figure 22.19 General layout of a power plant, station grounding grid, and switchyard grounding grid etc.

Figure 22.20 A simplified layout of Figure 22.19, illustrating the sharing of fault current by the station grounding grid and the switchyard grounding grid on fault...

Estimating the value of ground conductor length to design the grounding grid... 

Ground grid — System of interconnected bare conductors arranged in a pattern over a specified area and buried below the surface of the earth. 

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