On Wed, Jun 15, 2016 at 10:04:29AM -0400, D. Hugh Redelmeier via talk wrote:
Most people think 60Hz when they think AC. But I would guess that in a motor AC is timed to the rotation so that commutators (I think that's what they are called) can be eliminated.
Would that AC be 60Hz or would it be variable, matching some function of the motor's current speed?
Completely variable. My understanding is that at least on the freight trains they run the phase just ahead of the current motor position. That means if a wheel slips, it doesn't really speed up and damage the wheel and track, and looses all its power until it regains traction. Allows them to run right to the limit of the available traction unlike the DC motors. So a very simple motor with variable AC generated to match the current requirements of the motor perfectly. -- Len Sorensen