A transformer is a static
electrical device that
transfers energy by inductive
coupling between its
winding circuits. A varying
current in the primary
winding creates a varying
magnetic flux in the
transformer's core and thus
a varying magnetic flux
through the secondary
winding. This varying
magnetic flux induces a
varying electromotive force
(emf) or voltage in the
secondary winding.
Transformers range in size
from thumbnail-sized used
in microphones to units
weighing hundreds of tons
interconnecting the power
grid . A wide range of
transformer designs are used
in electronic and electric
power applications.
Transformers are essential
for the transmission,
distribution , and utilization
of electrical energy .
The transformer is based on
two principles: first, that an
electric current can produce
a magnetic field and second
that a changing magnetic
field within a coil of wire
induces a voltage across the
ends of the coil
(electromagnetic induction).
Changing the current in the
primary coil changes the
magnetic flux that is
developed. The changing
magnetic flux induces a
voltage in the secondary
coil.
Referring to the two figures
here, current passing
through the primary coil
creates a magnetic field. The
primary and secondary coils
are wrapped around a core
of very high magnetic
permeability , usually iron ,[d]
so that most of the magnetic
flux passes through both the
primary and secondary coils.
Any secondary winding
connected load causes
current and voltage
induction from primary to
secondary circuits in
indicated directions.
