ground grid fence connection

[cmelguet]

We have a 110/13.8kv 50 Hz substation and a 69/4.16 kV 60 Hz substation all surrounded by the same fence. The ground grid for both substations cover an area much smaller than the area surrounded by the fence. In the IEEE 80 it is recommended that the ground grid extend 1 m out of the fence perimiter, something that is not possible in this case. Should I connect the fence to the ground grid? Should I leave the fence with no connection to the grid?. How i deal with the problem that if I connect the fence with the ground grid, in case of a fault the fence will be at the grid potencial while the earth at the bottom of the fence will have a diferent potencial producing quite a big touchvoltage. On the other hand, should I connect the 60 HZ and the 50 Hz ground grids ?

 

[jghrist]

You need to check touch- and step-voltages, but generally, you will need to either

- isolate the portion of fence that is not near the substation grid, with insulating sections or,
- extend perimeter grid wires along the fence, inside and outside if necessary for touch-voltage.

If the two substations are not so far apart to make it too expensive, it would be best to connect the two grids. This will improve performance of each of them.