Page 71 - Solutions Manual to accompany Electric Machinery Fundamentals

where V  V  P a / . Since this is a Y- transformer bank, the line voltage V ab on the primary side is
S 
V ab  V A  V B  V  P 0  V  P  120   3V  P 30 

and the voltage V a  b  V A  V S  0  . Note that the line voltage on the secondary side lags the line
voltage on the primary side by 30.
2-22. Prove that the three-phase system of voltages on the secondary of the -Y transformer shown in Figure 2-
37c lags the three-phase system of voltages on the primary of the transformer by 30°.
SOLUTION The figure is reproduced below:

V A

V '
A

+ +

V B V '
B
- -

+ +

V V '
C C
- -

Assume that the phase voltages on the primary side are given by
V A  V  P 0  V B  V  P  120  V C  V  P 120 

Then the phase voltages on the secondary side are given by
  
V A  V S  0  V B  V S   120  V C  V S  120 

where V  V  P a / . Since this is a -Y transformer bank, the line voltage V ab on the primary side is
S 
just equal to V A  V  P 0  . The line voltage on the secondary side is given by

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