It would help if you gave the context where the term "fault level" was used. It could refer to the available fault at the primary terminals, the maximum through fault on the secondary side (considering an infinite bus - zero system impedance - on the high side), or the available fault on the low side with primary system impedance considered.
Fault level at a bus or at a transformer or at any other part of the system refers to the same. It is the MVA / current that will appear at the terminal of the equipment wheneven falut occurs. May be you can define it for a Balanced fault ( 3 phase to ground) and un balanced fault ( sigle line to ground) By conducting studies prior to the commissioning you can be aware of the fault levels in the system and can think of designing Primary grounding resistance / reactance or secondary grounding resistance. The fault level of the system connected to grid through a low impedance transformer is high the same is true in the case of parallel connected transformers ( so people always not operate the gris transformes in parallel)
hope this will help and sorry if it is out of context..
-nag400
The fault level of any transformer can be calculated by simple formula: (rated MVA capacity of Transformer / % impedance of Transformer). This gives the maximum fault level offered by any trf considering infinite bus at trf primary side
Just a slight clarification to RAgrawal's comment - The impedance of the transformer must be in per unit (%/100) and must be on the same MVA base as the numerator of the equation. This may or may not be the same as the rated MVA.
