I have drafted a AC combiner box for string inverters. Each string has its own protection (MCCB). So any fault occurring on a particular string will help in islanding the rest of the strings. Is it necessary to provide a separate protection at bus level i.e. a separate switch-gear at the AC bus to mitigate the fault ? Moreover the transformer at the upstream of the bus will have its own protection.
P.S. The AC combiner box is intended to have string PCS rated at 63kW and the bus current will be 1313 A. The downstream of PCS is connected to a PV string which is not shown in single line diagram.