3-8
Single-phase alternators are found in many applications. They are most often used when the loads
being driven are relatively light. The reason for this will be more apparent as we get into multiphase
alternators (also called polyphase).
Power that is used in homes, shops, and ships to operate portable tools and small appliances is
single-phase power. Single-phase power alternators always generate single-phase power. However, all
single-phase power does not come from single-phase alternators. This will sound more reasonable to you
as we get into the next subjects.
Q9. What does the term single phase indicate?
Q10. In single-phase alternators, in order for the voltages induced in all the armature windings to add
together for a single output, how must the windings be connected?
TWO-PHASE ALTERNATORS
Two phase implies two voltages if we apply our new definition of phase. And, it’s that simple. A
two-phase alternator is designed to produce two completely separate voltages. Each voltage, by itself,
may be considered as a single-phase voltage. Each is generated completely independent of the other.
Certain advantages are gained. These and the mechanics of generation will be covered in the following
paragraphs.
Generation of Two-Phase Power
Figure 3-6 shows a simplified two-pole, two-phase alternator. Note that the windings of the two
phases are physically at right angles (90º ) to each other. You would expect the outputs of each phase to
be 90º apart, which they are. The graph shows the two phases to be 90º apart, with A leading B. Note
that by using our original definition of phase (from previous modules), we could say that A and B are 90º
out of phase. There will always be 90º between the phases of a two-phase alternator. This is by design.
Figure 3-6.—Two-phase alternator.
