Ground wire along MV cables ?

[lz5pl]

Yesterday I examined design drawings of 33 kV cable grid for a windfarm. I found that grounding wire along the complete cable routes is provided. Wire is 70 sq.mm bare copper, installed in the trench close to the cables. When more that one MV cables are in parallel in one trench separate ground wires are provided for each cable.
It is a bit curious for me what these ground wires are intended for? I see such solution for a first time, but it seems it is typical for wind farms - I was told that the same is applied for each windfarm in construction here.

Could somebody give an explanation on the matter? And also what is the criteria for dimensioning of this ground wire?

------------------------
It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant

 

[dpc]

I would assume it is to provide a low impedance path for any ground fault current. The ground wire needs to run in close proximity to the phase conductors to reduce reactance.

In the US, the NEC does not allow use of standard shield conductors to be used as an "equipment grounding conductor". (I am not talking about concentric neutrals.)

The sizing criteria is based on being able to handle the expected maximum fault current without damage.

David Castor

http://www.cvoes.com