Date   : Wed, 23 Nov 1983 14:59:27 EST
From   : David Towson (CSD) <towson@amsaa>
Subject: Re: Transformers and European Current

David - The answer to your constant-voltage transformer question becomes
self-evident as soon as you hear the other name for them:  They are also
known as "ferro-resonant transformers".  Their operation depends on a tuned
circuit whose resonant frequency is slightly off the operating frequency.
As the line voltage input changes, the amount of core flux changes, and since
the relationship of core flux to exciting current (which results from the
applied voltage) is non-linear for iron-core inductors, the inductance of a
choke (inductor) in series with the transformer part itself (it's all inside
the box) changes and this changes the voltage actually applied to the trans-
former.  The thing is set up so that the change is in the right direction to
adjust the voltage to near what it should be coming out of the unit.  When
you run it on 50 HZ, you totally mess up the resonant action, which is tuned
for 60 HZ.  And that's the rest of the story.


Dave