earthing connections 2

[powercam]

hi again,
can the earth grid from a windfarm be connected to the substation earthgrid (10 km away ) via the cable earth sheaths? the fault current at the substation is 10kA,
will the cable heat when a earthfault occurs? will the earth sheath handle 10 kA? the cable from the customer's windfarm is 20kv. each wind turbine is also interconnected via earth sheaths and then eventually connected to our substation.
thanks

 

[cuky2000]

First a decision should be made if the cable sheath is grounded at one end, both ends or at multiple grounded points based in calculation and expected system performance.

In the event of ground fault, if both ends are grounded, current will flow in the cable sheath. Under normal conditions, circulating current may be expected causing reduction on the cable carrying current capacity.


On the other hand, for one end grounded, current do not flow in the sheath but the voltage will rise to level that need to be checked.

 

[mc5w]

Normally, there should be an equipment grounding conductor running along with the underground cable in a modern installation. This would be sized a minimum of 50% of the phase conductors which is standard practice for over 600 volts. The cable shields would be connected 1 end only of connected at both ends.

One thing that you do NOT want on a modern system is for the earth or water mains to be serving as the sole equipment grounding conductor. I have seen what happens as far as step and tingle voltage that occur when a service neutral is open or an underground branch circuit fails and leaks electricity into the soil.

Mike Cole, mc5w@earthlink.net