Maximum fault level is simply the maximum current that can flow during a fault. This is different from normal or rated current (fault current is much, much higher but generally only lasts a short period of time before protective devices such as fuses or MCBs operate to stop the flow of current). Its common limiting factor is the impedance of the line between the fault and the power source (such as a generator, battery, etc).

Have a look at the basics of fault current and generator or power grid current into a fault. I think you have missed a section on basic power transmission and distribution theory.

hi,

if we have T/F of 30 MVA, what rating of gerenator should we connected with this transformer.

What is T/F? It is not any industry standard acronym I am familiar with. A google search produced the following

None of which mean anything to me.

Could you explain in more detail please.

T/F stand for transformer.