in article snipped-for-privacy@news.stanford.edu, AES/newspost at snipped-for-privacy@stanford.edu wrote on 10/19/03 8:53 AM:
> A low-tech version of this high-tech route is to find a ferroresonant
>> "constant voltage" transformer whose output rating is equal to or a bit
>> higher than the set of bulbs you want to power. These are large and >
>> They *also* have inherent current limiting. No matter how heavy a load
>> you connect to their output, including a dead short, the output current
>> is limited to about twice the nominal rating of the transformer. The
>> transformer will hum loudly, but it won't burn up or be damaged by a
>> short of any reasonable duration.
>
>> Now, the CV transformer I'm talking about has no active parts other than
>> a transformer and one or more capacitors. There are no electronics. >
>
> Seriously OT, but these devices are of considerable conceptual interest.
> They are in essence "parametric oscillators" (at least some of them, the
> ones I know about are).
>
> The core of the device is not actually a transformer, but rather a big
> inductance that looks much like and is physically made like a big iron
> transformer. This inductance, which would be essentially the output
> winding of the transformer if it were a transformer, is paired with an
> equally big capacitance to make an LC circuit resonant at 60 Hz (for
> U.S. versions anyway).
>
> The input windings on the transformer are arranged such that they induce
> no voltage in the output winding, for example by counter-winding two
> series-connected input coils on the input leg of the transformer so they
> cancel each other. Instead of inducing an output voltage, the input
> current merely saturates the iron underneath these coils, thus
> time-modulating the L value in the resonant circuit -- and note that
> this happens at twice the input frequency, i.e. at 120 rather than 60
> Hz, since current in either direction tends to saturate the iron. >
> So, you have an LC circuit resonant at 60 Hz, with one of its reactive
> elements modulated in value at 120 Hz, and that's the essential
> condition to have a so-called "degenerate parametric oscillator". If
> the modulation is strong enough compared to the losses in the circuit,
> it will break into parametric oscillation at 60 Hz, and that's what
> drives the load. If you put on too much load -- including a dead short
> -- that kills the oscillation, thus giving you complete short-circuit or
> overload protection.
>
> This device thus operates on exactly the same basic parametric principle
> that governs how a child pumps a swing; radio-frequency "varactor diode"
> amplifiers (variable C instead of L) that used to be used as very low
> noise RF receivers a few decades back; and optical parametric amplifiers
> using nonlinear crystals that split "pump" photons into "signal" and
> "idler" photons and are routinely used to generate tunable optical
> signals at wavelengths where tunable lasers are not readily available.
> It's a neat invention.
>
> A guy named Kent Wanlass (one of two Wanlass brothers) may have invented
> it, or at least made and sold these several decades ago.
These paraformers, as they were called by Wanlass, are not the equivalent of voltage regulating transformers built by Sola or Wabash.
There is another arrangement of interest. Steinmetz came up with what he called monocylic circuits. They convert constant voltage to constant current and vice versa. They were used in the days when street lights were run in series.
The system is based upon resonant ciruits. For example, a series circuit of an inductor in series with a capacitor tuned to the line frequency can be used. Output is taken from the junction between the inductor and capacitor. For no load, the output voltage becomes very large while the current drawn from the line also gets large. Saturating inductors were used to limit the voltage rise. If the load is a short circuit, current is limited by the current through only one of the reactors. Line current is small.
A transformer can be built in which purposeful leakage reactance resonates with a capacitor. Thus, resonance by itself is not necessary to provide the entire voltage boost.
If a monocyclic circuit is used with rectifiers, capacitor banks can be charged at close to unity power factor. When the capacitorss are intially uncharged, there is no inrush of current. Current drawn from the line starts low and increases in proportion to the voltage on the capacitors.
Remember, the constant (ac) current into the rectifier goes along with a rectifiec current flow.
Modern capacitor charging supplies usually are switching supplies. At high frequency, the reactors rquired to temporarily store energy that would otherwise be dissipated can be made small. Monocyclic circuits can be used for this purpose.
Bill