Possible Fix: Replace the IDG that drops off line when the other one is taken off line.
Tip: It is probable that the GCU will only log a BTB fault, and not a IDG fault. The generator will not trip if the Bus XFR switch is set to “OFF” position.
Reason: The normal AMP load of a engine generator while it is on-line is 35-40 amps, when the other generator is selected off line the remaining generator’s load goes up to 75-80 amps. A weak IDG will not be able to handle the increased load required when the BUS transfer Kicks in.
Applicable Reference: AMM 24-11-11
Thanks to Tom S. for his input !