Chapter 12 Electromagnetic Induction
225
Eddy currents cannot be eliminated.
However, there are several things that can be
done to reduce them. Reducing the thickness
of the steel laminations that make up the core
will reduce eddy currents. Thick laminations
allow for larger loops and larger eddy currents.
Another way to reduce eddy currents is to
coat each metal strip with varnish or oxide,
similar to capacitor construction. This insula-
tion separates each piece in the stacked core.
Primary and secondary windings are made
of copper wire, Figure 12-22, or aluminum
strip, Figure 12-23, depending on the size of the
transformer. The larger transformers, usually
found on poles in local neighborhoods, use
the aluminum strip. The wire is coated with
an insulating material such as varnish. Notice
that the layers of the windings must also be
separated by an insulating material which is a
thermally coated paper. The insulating mate-
rial on the wire and between its layers is neces-
sary to prevent short circuits in and between
the windings.
The windings and cores are bolted or
banded together. The larger transformers
are put into cans, fi lled with cooling oil,
and prepared for shipping. The cooling oil
reduces heat after the transformer is put into
operation. All these steps are necessary to
keep the core material as close together as
possible to reduce eddy currents. The insu-
lation prevents short circuits. Reducing heat,
Figure 12-21. Alternating current fl ow in the
transformer core breaks down into tiny loops or
eddy currents.
Eddy currents
Laminated pieces
of core
Varnish
or oxide
Figure 12-22. Transformer windings made of
copper wire. (Power Partners, Inc.)
Copper
wire
Insulating
material
Figure 12-23. Transformer windings made of
aluminum strips. (Power Partners, Inc.)
Aluminum
strip
Insulating
material