GENERATOR

Portable Generator Familiarization & Troubleshooting Guide
Section 1 • Generator Fundamentals
SIMPLE ALTERNATOR OPERATION
Simple Alternator
In an alternator (Figure 1.27), a revolving magnetic field
called a rotor is moved through a stationary coil of wires
called a stator.This movement induces an electro-motive
force (EMF) into the stator coils.
Figure 1.27 — Simple Revolving Field Alternator
The Revolving Magnetic Field
The rotor is essentially an electro-magnet.The flow of
direct current (DC) through its windings creates a magnetic
field around the rotor core (Figure 1.28).The strength of this
magnetic field can be increased by:
• Forming the rotor wires into a coil.
• Increasing the wire size.
• Increasing the current flow through the rotor wires.
Figure 1.28 — Basic Principles Of Operation
As the magnetic lines of flux cut across the stationary
windings, a difference in electrical “potential” is induced into
the stator windings.When a complete circuit is formed (by
connecting a load to the stator windings) current flow
occurs.The current (in amperes) delivered to the load is
affected by:
• The number of wire turns in the stator.
• The strength of the magnetic field in the rotor.
The Stationary Magnetic Field
The number of wire turns in a stator winding are
determined when it is manufactured.A typical stator
assembly may be a single phase type, or a 3-phase type, as
previously discussed.The greater the number of wire turns
in the stator, the greater the induced EMF in the stator.This
is because the magnetic field of the rotor has more wire
turns to cut through on the stator.
The number of wire turns in a rotor, as well as the wire size,
are established when the rotor is manufactured.When the
alternator is operating, you can vary the strength of the
rotor’s magnetic field by increasing or decreasing the current
flow through the rotor windings.Thus, by controlling
current flow through the rotor windings, the EMF
induced into the stator windings can be regulated
and/or controlled. Because EMF (electro-motive force) is
the equivalent of voltage, it can then be said that voltage
regulation is accomplished by controlling rotor winding
current flow.
Several methods may be employed to regulate current flow
through rotor windings.They include:
• Direct Excitation.
• Reactor.
• Electronic Voltage Regulator.
• Brushless/Capacitor.
17