Thanks for the information to consider. Especially that the Synch relays may not be suitable. I was thinking that the synch relay would prevent the occurance of the diode failures.
The factory AVR Unregulated (Cct cards not connected) voltage droop is No load 495V/61.5Hz to 472V/58.5Hz at full...
We have been rectifying the above fault on machines in a marine application.
The machines are a SIEMENS 1FR6 454
1800 Rpm 450V 60 Hz 812 kVA @ 0.8 PF.
They are usually configured with at least 2 running insysnchronous at all times.
We suspect a contributing factor of the failure is the ships...