Alternating Current Power Systems 151
beginning of one phase winding is connected to the end of the adjacent
phase winding. Thus, the beginnings and ends of all adjacent phase wind-
ings are connected together. The voltage, current, and power character-
istics of three-phase wye and delta connections were discussed earlier in
Chapter 2.Advantages of Three-phase Power
Three-phase power is used primarily for industrial and commercial ap-
plications. Many types of industrial equipment use three-phase AC pow-
er because the power produced by a three-phase voltage source, as com-
pared to single-phase power, is less pulsating. You can see this effect by
observing that a peak voltage occurs every 120° in the three-phase wave-
form in Figure 6-9. A single-phase voltage has a peak voltage only once ev-
ery 360° (Figure 6-3). This comparison is somewhat similar to comparing
the power developed by an eight-cylinder engine to the power developed
by a four-cylinder engine. The eight-cylinder engine provides smoother,
less-pulsating power. The effect of smoother power development on elec-
tric motors (with three-phase voltage applied) is that it produces a more
uniform torque in the motor. This factor is very important for the large mo-
tors that are used in industry.
Three separate single-phase voltages can be derived from a three-Figure 6-11. Simplified drawing of the stator of a three-phase generator that is
connected in a delta configuration