HOW THE TRANSFORMER
WORKS
A clear understanding of how transformers work is
necessary in order to wire them properly in an electrical
system. Understanding input and output current and
grounding are particularly troublesome. A dual-voltage
transformer can be ruined when power is applied, if the
connections are made improperly.
An important property of electricity is that a magnetic
field is produced around a wire in which electrical
current is flowing, Figure 14-3. The more current that
flows, the stronger is the magnetic field. An even
stronger magnetic field can be produced by winding the
wire into a coil. Now the magnetic fields of adjacent
wires add together to form one strong magnetic field.
The electrical current flowing in a transformer is alternating
current. The current flows first in one direction,
stops, then reverses and flows in the other direction. The magnetic field around the winding is constantly
in motion. Figure 14-4 shows the magnetic field during
one cycle. Notice that the north and south poles of the
magnetic field reverse when the flow of current reverses.
Another property of electricity is important to the
operation of a transformer. When a magnetic field moves
across a wire, a voltage is induced into the wire, Figure
14-5. If the wire forms a complete circuit, current will
flow in the wire. If a second coil of wire is placed in a
moving magnetic field, then a voltage will be induced in
this second coil, Figure 14-6. This phenomenon is callege
mutual induction. Alternating current in one winding
produces a moving magnetic field that induces a voltage
in a second winding. Electrical energy is converted into'
magnetic field and then converted back into electrical
energy in a second winding. The trick is to do this with
little or no loss of energy.
The magnetic field loses strength quickly in air
therefore, a special steel core is used. The core is com
posed of thin sheets of a silicon-steel alloy. The magnetic field is concentrated in the core, and energy losses
are reduced to a minimum. Figure 14-6 shows the tw<
winding separated. Most transformers have one winding placed directly over the other to further reduce th(
loss of energy, as shown in Figure 14-7.