Cable Fault Current 1

[genhead]

Where multiple low voltage generators are connected in parallel (say, 4 x 1.5MW, 400v) the fault current obviously gets extremely high. Whilst switchgear is available to cope with these high fault levels, how is the cable protected? If the protection settings are sensitive enough to keep the downstream cable out of its damage curve, is the cable adequately protected? Or is there more to it? What about let-through? (Upping the voltage is not an option).

 

[davidbeach]

Don't look at the damage line for a single conductor when you have more than two in parallel; look at N-1 conductors in parallel based on the fault current for a fault at the far end of the run.

The damage curve is for protection against damage due to through faults. If the conductor itself has a fault it is toast no matter where the damage curve. That's why you needn't worry about the single conductor damage curve.

The use of N-1 conductors worth of damage curve is so that if you have a fault on one conductor near the far end the remaining conductors are protected against damage as they feed fault current to the far bus and back to the fault.

You're right, you can't protect the single conductor damage line when you have/need several in parallel, but as I said it also isn't necessary to do so either.