Does anyone know when the brushless Ac generator became commonly available? (Brushless as opposed to the older generators that used brushes for the excitor)

 

What do you mean by commonly available? According to Wikipedia they have been available for more than 100 years. They were widely used in automobiles beginning in 1960 (source: Wikipedia).

John

 

I mean for power production not vehicle alternators

 

I mean for power production not vehicle alternators

I saw them being used in the far east from the 80's.

As generator output in power production are rated to hundreds of MWs, their rotor field current often run to many thousands of amperes.

With brushless excitation, the excitation power is transferred from a stationary field into a rotating armature winding at one end of the generator rotor. It is then rectified into DC and fed to the main rotor winding. A whole array of high power diodes and protection fuses is required on the rotor for this rectification to work and the whole setup, as part of the rotor, rotates at either 3000 or 3600 rpm, depending on 50Hz or 60Hz output.

Imagine diodes and fuses working at great centripetal forces when rotating at such high speed. To give you some idea just a single fuse alone would cost US$1000~2000 and there can be as many as 48 of them in a setup.