Yes - the breakers are series rated. A technical explanation is the feeder breaker will draw an arc introducing a large(r) impedance into the circuit which may prevent the upstream breaker from un-latching.
sajujsam:
Lee's energy equation was derived for medium voltages over 15kV as it assumes little arcing impedance. It is a very conservative estimate for incident energy, but has nothing to do with calculating the bolted fault current.
Before you get into the arcing current and subsequent...
If you are doing this by hand, a good reference to follow would be the "MVA method" (google it). It is not an exact method, but it gives you a good indication of the fault magnitude at your desired bus. Like Bill said, induction motors will become induction generators and feed into the fault...
The utility will provide you will the equivalent Thevenin impedance at the point of common coupling (or will provide 3-P fault current and X/R ratio). You will then need to calculate the bolted three phase fault currents at all of the busses applicable in your study. You'll need to use something...
