controlling the generator output voltage is to vary the current through
the
windings of the electromagnets and thus vary the strength of the field.
12.
ALTERNATING CURRENT
When we use rotating mechanical devices to produce the large amounts of current
needed for practical uses, we find that the mechanical devices produce essentially
an alternating current (ac); that is, the current flows first one way and then
reverses itself and flows the other way through the conductor. The simplest source
of mechanically produced ac energy is the ac generator. It produces this energy by
a combination of electromagnets and rotating coils of wire.
a. Basic Ac Generator. The basic ac generator is made up of an electromagnet
that sets up a strong magnetic field between two pole pieces.
The coil of wire
then spins between these two pole pieces to develop a voltage as a result of the
wire cutting the lines of force in the magnetic field.
The ends of the coil of
wire are brought out to sliprings so that the voltage developed by the coil may be
conveniently attached to circuits that will use the voltage.
The circuits so
connected are collectively called the load. The sliprings of a basic ac generator
are shown connected to a galvanometer in figure 16. This instrument will measure
the amount and direction of the current developed by the generator.
Figure 16.
Generation of ac voltage.
308
20
Previous Page
