Lasted edited by Andrew Munsey, updated on June 14, 2016 at 10:02 pm.
> Plz educate me what do you mean by magnetic shunt and how it prevents impact to the primary?
In normal transfos, you wind the secondary on top of the primary. In FRs,
you wind the primary on bottom half of transfo, and secondary on top half,
with a magnetic shunt in between. This magnetic shunt is nothing else than
simply the same laminate really shortcutting the magnetic path of the
secondary. The thickness of this shunt is less than half of the transformer
core thickness, else all flux would be 'shunted'.
So you could see this transfo as containing 2 separate magnetic paths with a
limited coupling between them.
The conventional reason of using a FR is because any change in the primary
voltage will not translate into changes in the saturated secondary voltage,
and voltage regulation results.
Normally, core saturation in a transformer results in distortion of the
sinewave shape, and the FR is no exception. To combat this side effect, FRs
have an auxiliary secondary winding paralleled with one or more capacitors,
forming a resonant circuit tuned to the power supply frequency. This "tank
circuit" serves as a filter to reject harmonics created by the core
saturation, and provides the added benefit of storing energy in the form of
AC oscillations, which is available for sustaining output winding voltage
for brief periods of input voltage loss (milliseconds' worth of time, but
certainly better than nothing).
In addition to blocking harmonics created by the saturated core, this
resonant circuit also "filters out" harmonic frequencies generated by
nonlinear (switching) loads in the secondary winding circuit and any
harmonics present in the source voltage, providing "clean" power to the
When a "ferro" is fully loaded, meaning that it is having maximum current
drawn from it, the output voltage wave form approaches that of a sine wave.
On the other hand, when the load is light, the wave form takes on more of a
quasi square wave. This is a result of the transformer's effort to keep the
output voltage as constant as possible, which is the very essence of the
So far a conventional FR use.... End of education... )
Now the interesting thing...
We DON'T use it for voltage regulation nor with the auxiliary winding (just
with the primary and main secondary), but purely for resonance creation
(with high Q) without impact to primary. You can resonate the secondary (so
creating high current and voltage). In a normal transfo, this will impact
total flux and as such also the primary. In an FR, because of the shunt,
this resonance and as a consequence the saturation remains within the
secondary magnetic loop (because of the laminate shunt). So you can get the
ferroresonance effect in the secondary without impacting the primary.
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