Maximum short circuit of an assumed substation is related to network fault level which connected to it. The fault level of an electrical network is the capacity of the source of supply to feed the faulty circuit, and is represented in kVA or MVA. Some typical values are noted below: 
To characterise the short-circuit infeed from one short-circuit source, a group of such sources or an entire system, the concept of short-circuit fault level is useful: Short-circuit fault level(MVA) =?3VPhase