I write this not as a question but as as a guide how to handle a three phase rotataion problem which occured at our three phase quattro system in Africa:
The system is based on 6 Quattros configured as "big three phase UPS", a large battery bank and a backup Diesel generator.
Occasionally the grid on AC1 IN fails, the systems switches over to the battery bank and as last action, a backup Diesel generator on AC2 IN is automatically started in case the grid failure is too long and the batteries are getting empty.
Suddenly, the grid showed correct voltages on all three phases on AC1 inputs (!) but the inverters did not accept the input power and switched to inverter mode and kept draining the batteries.
Upon reaching the defined low level value in the GX the backup Diesel generator was correctly started but the Quattros did not measure any input voltages from the generator and thus did continue to drain the batteries until they were empty and all shutdown.
Upon disconnecting the grid by opening the circuit breakers, the AC1 IN voltages went down to 0V and after restart of the whole system the Diesel generator was correctly detected on AC2 IN and system went up again.
After investing the case the following root cause was found: The grid operator has changed two phases by mistake during maintenance (=opposite three phase turn direction).
This leads to the situation that the Quattros "see" all three correct input voltages on all three phases on AC1 IN but all currents remain at zero because input not usable. System remains in inverter mode. At the same time, a started generator input power on AC2 is not detected by the Quattros because reasonable voltages from the grid on AC1 IN are present (but not usable!)
How to identify such a case:
If all three input voltages are present and in a reasonable range check first the voltages between all three phases. It must be in the 400V range, otherwise you don't have a correct three phase grid input.
If the voltages between all phases are correct then it is likely the wrong rotation direction not matching to your three phase system programming! --> Exchange two phases!
In order to enable the Quattro to use an alternative three phase power source like a Diesel generator on the other AC input while such a special grid rotation error exists, cut off the unaccepted power input source then restart the whole system and it will accept power on the alternative source.