THREE-PHASE CIRCUITS
Basic AC Power
Figure 10 Three-Phase AC
Three-phase equipment (motors, transformers, etc.) weighs less than single-phase equipment of
the same power rating. They have a wide range of voltages and can be used for single-phase
loads. Three-phase equipment is smaller in size, weighs less, and is more efficient than
single-phase equipment.
Three-phase systems can be connected in two different ways. If the three common ends of each
phase are connected at a common point and the other three ends are connected to a 3f line, it
is called a wye, or Y-, connection (Figure 11). If the three phases are connected in series to form
a closed loop, it is called a delta, or D-, connection.
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