Figure 3-22.--Three-phase, delt-connected system.
the delta connection. In a delta-connected ac generator,
the connections are made as follows:
The start end of one phase winding is connected
to the finish end of the third.
Figure 3-23.--Waves and vectors of alternating current and
The start of the third phase winding is connected
voltage in a circuit containing only resistance.
to the finish of the second phase winding.
The magnitude of a vector is represented by its
The start of the second phase winding is
length: the longer the vector, the higher its magnitude.
connected to the finish of the first phase winding.
The direction in which the vector acts is shown by the
direction of the arrow.
The three junction points are connected to the line wires
leading to the load.
Alternating current and voltage vectors are
The three-phase, delta-connected ac generator is
referenced to a coordinate plane, which represents 360
electrical degrees. By agreement, counterclockwise
connected to a three-phase, three-wire circuit, which
rotation represents positive and clockwise rotation
supplies a three-phase, delta-connected load at the
represents negative. The horizontal axis of an analysis
right-hand end of the three-phase line. Because the
diagram represents the reference axis, and any vectors
phases are connected directly across the line wires,
in the diagram are referenced to this position.
phase voltage is equal to line voltage. When the
generator phases are properly connected in delta, no
In figure 3-23, you can that the voltage (E) and the
appreciable current flows within the delta loop when
current (I) are in phase with one another. Since the two
there is no external load connected to the generator. If
values are in phase, the angle between them is 0 in the
any one of the phases is reversed with respect to its
vector diagram. This represents a purely resistive ac
correct connection a short-circuit current flows within
circuit.
the windings of no load, causing damage to the
Look at figure 3-24. Here, you can see that the
windings.
voltage (E) is leading the current (1) by degrees. You
Vector Analysis
A scalar quantity has only one facet, magnitude. On
the other hand, a vector quantity has more than one facet,
as shown by a vector diagram. In the vector diagram,
the vector is shown by a line drawn to scale with an
arrow head to indicate direction. This line showing a
vector quantity indicates both magnitude and direction.
Good examples of both quantities are shown below:
Figure 3-24.--Waves and vectors of alternating current and
voltage in a circuit containing only inductance.
3-17
