Generac 86640 - Manual (Page 5)

Section 1.1- HOW GENERATORS PRODUCE ELECTRICITY
Magnetic Induction
It has long been №own that a relationship exists between
magnetism and electricity. Revolving field AC generators
depend on this relationship for their operation. If generator
problems are to be properly diagnosed, the service techriician
must understand this relationship. Magnetism can be used to
create an electrical voltage in a conductor. Conversely, elec­
trical current flow through a conductor will create a magnetic
field around that conductor.
See Figure 1, below. When a conductor is moved
through a magnetic field, an electromotive force (EMF or
voltage) is induced Into the conductor. Movement of the
magnetic field so that It cuts across the conductor will also
create a voltage In the conductor. If the ends of the conductor
are connected to form a complete circuit, current will flow
through the conductor. The direction in which the current
flows depends on the polarity of the magnetic field and the
direction in which the magnetic field (or conductor) is moved.
The amount of voltage Induced into the conductor depends
on the strength or concentration of the magnetic field, i.e., the
stronger the magnetic field, the higher the induced voltage.
See Rgure 2. When current flows through a conductor,
a magnetic field is created around that conductor. The
strength of the magnetic field depends on (a) the amount of
current flow, (b) the number of turns or loops in the conductor.
The polarity of the magnetic field depends on the direction of
current flow through the wire. The following facts should be
evident:
□ If current flow through a conductor can be regulated, the
strength of the magnetic field around the conductor can
be regulated.
D If the strength of a magnetic field can be regulated, the
amount of voltage induced into a conductor by such a
magnetic field can also be regulated.
A Simple AC Generator
Figure 3 represents a simple AC generator, in which the
rotating magnetic field (Rotor) Is a permanent magnet. As the
magnet rotates, its magnetic field cuts across a stationary coil
of wires called a STATOR. When the magnet’s North mag­
netic pole moves past the stator windings, current moves
through the wire in one direction. As the South magnetic pole
of the magnet passes the stator wires, current reverses itself
and moves through the stator in the opposite direction.
in the simple generator shown, the strength of the mag­
net is fixed. That \ the magnetic field strength cannot be
changed since a permanent magnet is used. Because the
magnetic field strength is fixed, the voltage induced into the
stator coil is constant
If some method of regulating the magnetic field strength
of the magnetic could be found, the voltage induced into the
stator coil could be regulated as well.
Figure 3. A Simple Revolving Field Generator
Paga 1.1-1