four-pole
generator
where
one
More
specifically,
the
current
mechanical revolution of the loop
produced
by
these
is
constitutes two cycles.
To produce
single-phase because only one source
60-cycle
current,
this
generator
of induced current (one loop or coil)
rotates at 1800 rpm, half as fast as
was used between the poles.
Now, by
the two-pole type.
using three coils or loops, current is
induced in each one by the poles and
4.
CONSTANT POTENTIAL SYSTEMS
the resulting effect is three single-
phase currents acting in the same
The most common type of system for
circuit as shown by figure 4.
Note
electrical
distribution
is
the
that the illustration shows a much
constant potential type where the
smoother sequence of impulses than the
voltage
is
kept
as
constant
as
earlier illustration of single-phase
possible and the current varies with
current.
The
difference
may
be
variations in loads.
This system is
compared to the action of a two-
further subdivided into direct and
cylinder gasoline engine (single-phase
alternating
current
of
which
(as
current) as against a six-cylinder
previously stated) the direct current
engine (three-phase current).
The
type
is
seldom
used
and
will,
more phases or cylinders used, the
therefore, not be discussed.
The
smoother the power output.
This is
common
alternating
current
not the only advantage of three-phase
distribution systems employ another
current, as will be shown later.
variation
of
the
current
Single-phase current, however, is not
characteristics, known as three-phase
made obsolete by three-phase current.
current.
Previously described were
Each type of current has its own
the two-pole and multipole generators
specific application which is based on
the type of load to be served.
The
which produced alternating current.
following arrangements of single-phase
and three-phase currents are used in
distribution systems:
single-phase, two-wire
single-phase, three-wire
three-phase, three-wire
three-phase, four-wire
5.
SYSTEM NOTATION
Systems are identified by the number
of phases and wires and the voltage
between the wires.
For example,
figure 6 shows a single-phase, three-
wire 120/240 volt system. The correct
notation for this system is 1 3W
120/240V.
A three-phase four-wire
120/208V system would be shown as 3
4W 120/208V.
6.
SINGLE PHASE
Buildings
that
use
single-phase
current
are
those
containing
X-ray
machines
and
other
single-phase equipment, or buildings
Figure 4.
Three-phase current.
1-3
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