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Here is the problem:
An ac voltage of Vp is applied across the primary
coil, and if the secondary coil of a transformer
is connected across a load, most texts, if ever mentioned, have concluded that
there will be be an increase in current in the primary coil.
The reason:
The induced current in the secondary produces a
changing magnetic flux, which induces a current which will reduce the back
e.m.f. (i.e. in the same direction as the applied current due to Vp). As Vp is
fixed (fixed freq.), an increase in current in the primary would therefore imply
an increase in the rate of change of magnetic flux, hence greater induced
current in the secondary. Moreover, the back e.m.f. in the primary is also
increased! The greater induced current in the secondary now again reduces the
back e.m.f., increases current, increases back e.m.f. and the cycle repeats
itself.
One text (I think Tom Duncan, 4th edition)
mentioned that the situation would stablise when Vs = back e.m.f.,
why?
I think there's some confusions here. Can someone
offer a clearer perspective?
Regards,
Chow
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