ELECTRICAL VOLTAGES AVAILABLE
TESTING AND ADJUSTING
SUBJECT/TITLE:
AC Voltages Available from Caterpillar SR 4 Generators
BUSINESS:
Building Services, Material Handling, Marine, Agriculture
PRODUCT:
Generator Sets
Most generator set applications require that the electrical
output match one of several existing commercial
voltages and one of two frequencies. Where the
generator set is replacing, or supplementing commercial
power, the existing frequency and voltage characteristics
will determine generator selection. Where the generator
set is to be totally isolated from commercial power, the
proposed load (particularly motors) will determine
generated voltage and frequency. Practically all electric
motors above 5 hp are three-phase, and motors of
lesser horsepower can be single- or three-phase.
The more common commercial nominal voltages and
frequencies are:
60 Hz - Single-Phase/Three-Phase
120/208Y, 125/216Y, 127/220Y, 277/480Y, 120/240
60 Hz - Three-Phase Only
220, 240, 480, 575, 600
60 Hz - 3-Wire, Single-Phase Only
110/220, 115/230, 220/440
50 Hz - Single-Phase/Three-Phase
220/380Y, 230/400Y, 240/415Y
50 Hz - Three-Phase Only
460
Note: The slant (/) line indicates both voltages are
available at the same time. With the exception of the
60 Hz 3-wire single-phase 110/220 and 220/440
systems, all other dual voltage systems consist of a
single-phase lower voltage, and a three-phase
higher voltage.
Generally, voltages above about 220 volts originate from
a three-phase source. Commercial distribution is more
commonly three-phase which also permits use of single-
phase loads. Some distribution is single-phase. This
system is limited to single-phase loads only, unless
special transformer-capacitor equipment is used to
simulate or approach a three-phase voltage.
Larger industrial loads are usually three-phase, with
single-phase loads supplied from one or more of the
phases. The following diagrams show how commercial
distribution
transformer
secondary
windings
are
connected to obtain one of the above listed common
three-phase and single-phase voltages.
Figure 1
3-Phase Y, Wye, Star Common Voltages:
120/208Y; 125/216Y; 127/220Y;
230/380Y; 230/400Y; 240/415Y; 277/480Y
The listed lower voltages of this dual voltage system are
single-phase and can be obtained from any one Line
(L1, L2, L3) and the Neutra (N). The higher voltages are
three-phase and are obtained from L1, L2, L3.
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