Why new generators are lighter than old generators
Yet they are putting out more power...
“The primary in-flight electrical source on the 777 is a 120 kVA constant speed two-pole brushless alternator. This represents a 33% increase in capacity over the next largest electrical source on previous Boeing commercial jet transports, the 747-400, 757 and 767. The alternator in these machines is integrated with an axial gear differential/hydraulic constant speed drive. The speed on the 120 kVA machine maintains an average 24,000 rpm plus or minus about 1%. This is currently the lightest weight technology in kVA per pound for supplying a 400 Hz constant frequency system, actually weighing just slightly less than the 40 kVA drive/alternator on the earlier Model 727.
Minimizing weight has been achieved partly by increasing the alternator speed, partly by improved packaging and partly by switching from air cooling to oil cooling. The progression on Boeing airplanes has been from air-cooled 6000 rpm machines on the 707, 727, 737-100/200/300/400's and 8000 rpm machines on the 747-100/200, to oil-cooled 12,000 rpm machines on the 767, 757 and 740-400, and ultimately to 24,000 rpm machines on the 777. The 24,000 rpm constant speed Integrated Drive Generator, or IDG as it is referred to, was a mature technology also in service on the McDonnell Douglas MD-11 and Airbus A330.”
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