Pretty sure the IDG's are rated at 60KVA. The APU gen's are rated at 90KVA (different cooling).
I'm pretty sure you could be talking about the generators fitted to the 'classic' 747's whereby the generator was the same Part Num as the ones fitted to the APU yet on the main engine were driven by a seperate CSD (constant speed drive). Yes, there was less cooling air available in the cramped quarters under the engine cowls and output was approx 60KvA in this installation. APU had a dedicated cooling fan driven off gearbox to cool the gennies fitted up the back end.
Figures in post above are for the 747-400 with IDG'S fitted (CSD and generator all in one with dedicated oil cooling system). Same item is fitted to 767'S. Below is from the Maintenance Manual.
An integrated drive generator (IDG) is mounted on the aft face of the accessory gearbox at the 7 o’clock position. The IDG consists of a constant speed drive and a generator mounted side by side in a common housing. Other parts integral or mounted to the IDG are the scavenge filter, thermal relief valve, and pressure relief valve. The IDG converts the varing input speed of the engine into 115/200volt, 3-phase, 90 KVA, 400 ±5 Hz power. The IDG weighs approximately 120 pounds (54 kilograms).
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