Coordination and Short Circuit Study

[Fuselink]

Utility has provided us with maximum and minimum 3P and L-G short circuit values. Which one of the values id recommended to be used for fuse, Circuit breaker Short circuit rating as well as short circuit study and coordination. This will determine which values to be used in SKM as utility data.
I have seen that maximum available short circuits are used, however I always thought minimum short circuit is the one.

 

[jghrist]

Coordination has to be achieved throughout the range of available fault currents. In most cases, the coordinating intervals are smallest at high fault currents, but if this is not the case, then coordination must be checked at minimum faults. You also have to ensure that overcurrent pickups are set low enough to detect minimum faults.

If you are doing arc-flash analyses as well as coordination, the minimum fault levels are important because interrupting times are slower and arc-flash energy can be higher for lower fault currents.

 

[rbulsara]

Use maximum SC current values to determine the equipment short circuit current ratings (withstand rating or AIC ratings), while minumum short circut currents should be used for protective device coordination purposes as advised by jghrist earlier.