Originally Posted by
renard
Not from an electrical background, but advances in materials could play a part, just like in engines.
To a degree. But the main advances really are in rotor speed. Voltage produced in a winding is proportional to the number of turns of wire times the speed of magnetic flux change. Increase the speed of change (by upping the RPM) and you need fewer turns of wire. Fewer turns of wire need smaller slots in the generator stators and therefore smaller stators. The stators are the big (heavy) magnetic pieces. So weight savings here is significant.
On the 787, the main generators are connected directly to the engine gearbox and produce a frequency dependent on engine speed. Solid state converters are used to take this variable frequency power and produce 400Hz. The biggest weight savings here is the elimination of the hydro-mechanical constant speed drive either as a separate unit on older models or an IDG (Integrated Drive Generator) on the 767 and on.