Busbar Continuous Current Rating For Multiple Sources

If your bus is laid out like this, nothing needs to be over 5000 A:

(2.5 MVA of loads)-----(1DG)-----(bus tie)-----(2DG)-----(2.5 MVA of loads)

But in this case, if load MVA or a fault MVA on DG-1 load side bus section exceeds say 3 MVA, then it may lead to overheating of busbar as it will be fed by both DGs without exceeding their rated capacity.

Also my second question - is it necessary to have specific locations of DG & bus tie breakers? If my load feeders are fixed & no additional load would be put on then can I go ahead with 5000A bus sections and breaker locations to suit the DG set & LV board layout. This will help reduce DG incoming busduct length and no. of bends.

Do we need to consider fault situation of rating higher than say 3MVA but less than 5.5 MVA. Because all faults higher than 5.5 MVA will trip the DG breakers due to DG overcurrent / earth fault protection.

It depends upon your required applications and conditions as per your given details, there is no need to run both generators in synchronization mode. It is not required because your each generator can carry all the loads. so 5000A busbar is ok for the full loads. Go as<<<<< DG1----Bus-coupler------DG2>>>>> both DGs can be run parallel or If one DG is failed then buscoupler will allow the other DG to take the loads.

If both DGs are to be run in synchronized mode i.e. buscoupler will normally be in close condition then go for 10000 Amp bus bar. Yes it is practical.