From: dhky@shaw.ca   
      
   On 08/10/2013 9:58 AM, Salmon Egg wrote:   
   > In article , Don Kelly    
   > wrote:   
   >   
   >> There have been many, sometimes weird, devices based on the induction   
   >> motor- and, before modern electronics, many of them were intended for   
   >> speed control.   
   >> -   
   >   
   > I vaguely remember something called a "phase shifter." It had something   
   > to do with efficient operation of an induction motor far off synchronous   
   > speed. IIRC it used one or two additional rotating devices to maintain   
   > torque and/or decent power factor. Do you know anything about that, Don?   
   >   
   The phase shifter I referred to would simlpy change phase- it had a 1:1   
   turns ratio. However using it as an autotransformer would provide a   
   variable voltage   
   I don't know how a device external to the motor would improve efficiency   
   of the motor.  However- what you refer to may be a Schrage motor which   
   fed back from the rotor (apparently involving a second rotor and stator   
   winding to convert from slip frequency to line frequency (and with brush   
   shifting in between to shift phase as needed. )and would involve some   
   phase shifting. This machine could maintain torque over about a 10:1   
   speed range, possibly with decent efficiency(?) It was bulky and   
   complex- I did run one when an undergrad about 60 years ago and never   
   since met one, thankfully.   
      
   --   
   Don Kelly   
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