Alternating Current Analysis
263
R.3.80 The system voltages, as well as the loads in a 3 Φ system can be connected in either
a ∆ or a Y confi guration, as illustrated in Figures 3.43 through 3.46, where E 1 + E 2 +
E 3 = 0.
R.3.81 A balance system consists of a system where the load impedances are Z 1 = Z 2 = Z 3
in a Y confi guration, or when Z 4 = Z 5 = Z 6 in a ∆ confi guration; refer to Figures 3.42
through 3.46.
R.3.82 Standard circuit techniques such as loop or node equations can be used to analyze
polyphase systems (to determine currents or voltages).
R.3.83 When a 3 Φ system is connected to an unbalanced Y load, the neutral nodal point
referred by N is not at the neutral potential, and is labeled with an O. The change
in voltage between the balanced and the unbalanced case is referred as V ON , and is
referred to as the neutral displacement voltage.
FIGURE 3.42
3 Φ system with sequence ABC.
C
V AC
B
A
N
(N = Neutral
point)
V AB
V AB = V ∠120 °
V BC = V ∠0 °
V AN = D ∠90 °
V BN = D ∠−30 °
V CN = D ∠−150 °
V CA = V ∠240 °
D = V
3
FIGURE 3.43
3 Φ–Y system connected to a Y load.
Z 2
Z 3
Z 1
E 1
E 3
E 2
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7/23/2008 1:27:41 PM
7/23/2008 1:27:41 PM