You should not depend upon the primary side protection relays for a t/f secondary fault. The t/f ratio turns a secondary line/earth fault into a primary line-line fault.
The secondary protection should cover for major secondary faults.
The t/f will normally have specific protection e.g...
Regardless of whether the load is inductive or capacitive the load is more onerous to switch when compared with a purely resitive load (i.e unity power-factor).
The rated making capacity of a circuit-breaker is more arduous than the breaking capacity because of the potential XL/R ratio.
If you...
Look at the IEC 947-2 definitions for Iuc, Icw, Isc & Ibc.
ACB's:
Larger and heavier
More expensive
Maintainable components
Longer times fault for withstand capacity.
Can be used with IDMT protection relays
MCCBs:
Smaller and lighter
Please be carefull about the interpretation of fault...
IEC 947-2 covers Circuit-breakers. This has several definitions with which you need to become more familiar.
Icu = ultimate breaking capacity
Isu = rated service capacity
Icw = withstand capacity
Imc = current making capacity.
If you read the definitions and assess them they could be some...
consider the fault-level at the transformer terminals by assessment of the HV system and the t/f reactance.
Then consider the MCCB and ACB fault-making/breaking capacity.
The down stream breakers/fuses need to checked to discriminate with the ACB/MCCB.
