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Induction Regulators

At 04:04 PM 12/17/98 -0700, you wrote:
>Original Poster: Jim Monte <JDM95003-at-UCONNVM.UCONN.EDU> 
>
>
>Hi,
>
>>From what I read so far, this appears to be a conversion to a variable
>inductor, not a variac. :(   With the rotor stalled, the motor looks
>like a transformer with its secondary (the rotor) shorted.  Sliding the
>rotor out decreases the coupling between the primary and secondary.
>That sounds just like the variable air gap in a welder.  However, it
>would not be hard to keep the rotor from rotating assuming single phase
>power is applied to either a polyphase motor or a single-phase motor run
>windings only.  For these cases, the motor will remain stalled.  Does
>someone perhaps have more information on the motor -> variac conversion?


Hello all.

The device that Jim is referring to is called an induction regulator. The
regulator is similar in design to a wound-rotor induction motor but it is
essentially a transformer whose output voltage is varied by rotating its
secondary relative to the primary. 

The following reference is from "High Voltage - Measurement, Testing and
Design", ISBN: 0 471 90096 6

"The stator (primary) carries the current and the rotor (secondary) is
connected across the mains supply as follows:

                                      ________ H.V.
                                  || }
                                  || }
            stator                || }
            _______/__            || }
L.V._______|      /   |_________  || }
       |   |_____/____|         { || }
       |    ____/_____          { || } 
       |___|   /      |____     { || }
           |__/_______|   |     { || }
             /rotor       |     { || }
    ______________________|_____{ || }________ earth

                              step up 
                             transformer

With V as the supply voltage, the secondary voltage can be varied from -V
to V according to the position of hte rotor, which can be moved through
nearly 360 degrees. Thus the voltage applied to the primary of the step up
transformer can be adjusted from zero to 2V. Induction regulators can be
arranged for manual or automatic control but a disadvantage lies in their
high cost. Moreover, careful design of the unit is needed to avoid waveform
distortion but, nethertheless, such regulators find windspread use in
high-voltage laborotories."

The major advantage of the induction regulator is that unlike variacs, they
are practical for transformers over 5 kVA. Perhaps there are coilers or
power engineers on the list who can provide more information?

Safe coiling,

Gavin Hubbard