[CW] Alexanderson Alternator

[Ron W4BIN]

a 100 kHz Goldschmidt machine with P = 300 poles would require a rotor 
speed of only U = 5000 RPM, one-fourth that of an equivalent 
Alexanderson machine. 80% efficiency could be achieved, but in order to 
keep the leakage flux low enough to achieve this the machine required a 
very narrow clearance of 0.8 mm between the stator and rotor, which 
could weigh 5 tons and be moving at a peripheral speed of 200 meters per 
second.[3][4] Another challenge was that to reduce hysteresis losses in 
the iron rotor at radio frequencies, it had to be made of very thin foil 
laminations, .05 mm (.002 in) thick, separated by paper sheets,[3] so 
the rotor was more than 1/3 paper. No rotor of this construction had 
ever been used in a large machine. The limit of output frequency for 
Goldschmidt alternators, as well as other alternator technologies, was 
about 200 kHz. The mechanical problems ultimately limited the use of 
Goldschmidt machines.



   A 100 kHz Goldschmidt machine with P = 300 poles would require a 
rotor speed of only U = 5000 RPM, one-fourth that of an equivalent 
Alexanderson machine. 80% efficiency could be achieved, but in order to 
keep the leakage flux low enough to achieve this the machine required a 
very narrow clearance of 0.8 mm between the stator and rotor, which 
could weigh 5 tons and be moving at a peripheral speed of 200 meters per 
second.[3][4] Another challenge was that to reduce hysteresis losses in 
the iron rotor at radio frequencies, it had to be made of very thin foil 
laminations, .05 mm (.002 in) thick, separated by paper sheets,[3] so 
the rotor was more than 1/3 paper. No rotor of this construction had 
ever been used in a large machine. The limit of output frequency for 
Goldschmidt alternators, as well as other alternator technologies, was 
about 200 kHz. The mechanical problems ultimately limited the use of 
Goldschmidt machines.

   from:  https://en.wikipedia.org/wiki/Goldschmidt_alternator