It is very short time. isn't it ?

it is different case, if normally, two feeder operating.

In case two feeder operating. find out how many MVAsc Source Feeder 1 and MVAsc

Source Feeder 2.Then Parallelized it. That is MVAsc Bus.

For Example :

MVAsc Source feeder 1 = 2 MVA (depend on your impedance generator,ZO,Z1,Z2)

MVAsc Source feeder 2 = 2 MVA (depend on your impedance generator,ZO,Z1,Z2)

MVAsc Total : 1 MVA ≈ 17.5 kA

So Your Busbar Rating could be : 33kV, 50Hz,2000A, 3PH, 31.5kA Sym RMS, 3 Sec.

look, busbar rating 31.5kA could be flown Short Circuit current as big as 17.5 kA.

thank you

regards

Elect-Ok is right. It depends on time for which tie breaker will remain closed.Though to make the system failure proof , consider the parallel condition for calculation of short circuit. That will be the worst condition and it is better to design the system for worst condition. I will try to find the standard......

It is generally accepted practice to ensure that the phases of the two circuits match when closing one circuit into another. This minimises short circuit currents likely to cause the switchgear contacts being destroyed.

Keep in mind that if the two feeders come from different transformers that the impedance of the two transformers will be in parallel. This means a lower effective transformer impedance and a higher fault current in a short-circuit situation.

Any cabling running from there could have the potential of nearly double the amount of current compared to only one feeder open.