Basic AC Power
THREE-PHASE CIRCUITS
THREE-PHASE CIRCUITS
The design of three-phase AC circuits lends itself to a more efficient method of
producing and utilizing an AC voltage.
EO 1.5
STATE the reasons that three-phase power systems are
used in the industry.
EO 1.6
Given values for current, voltage, and power factor in a
three-phase system, CALCULATE the following:
a.
Real power
b.
Reactive power
c.
Apparent power
EO 1.7
Given a diagram of a wye- or delta-connected three-
phase
system,
DESCRIBE
the
voltage/current
relationships of the circuit.
EO 1.8
STATE the indications of an unbalanced load in a three-
phase power system.
Three-Phase Systems
A three-phase (3f) system is a combination of three single-phase systems. In a 3f balanced
system, power comes from a 3f AC generator that produces three separate and equal voltages,
each of which is 120° out of phase with the other voltages (Figure 10).
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