Page 67 - Solutions Manual to accompany Electric Machinery Fundamentals

 V 2  20,000 V 2

Z  P   8 k
base,P
S 50 kVA
The base impedance of this transformer referred to the secondary side is
 V 2  480 V 2

Z  S   4.608
base,S
S 50 kVA
The open circuit test yields the values for the excitation branch (referred to the secondary side):
I 4.10 A
Y   ,OC   0.00854 S
EX
V  ,OC 480 V
 P   620 W 
  cos  1  OC   cos   1     71.6

 V OC I OC    480 V 4.1 A  
Y EX  G  C jB  M 0.00854   71.6   0.00270  j 0.00810

R  C 1/ G  C 370 
X M  1/ B  M  123

The excitation branch elements can be expressed in per-unit as
370  123 
R   80.3 pu X   26.7 pu
C
4.608  M 4.608 
The short circuit test yields the values for the series impedances (referred to the primary side):
V 1130 V
Z  SC   869 
EQ
I SC 1.30 A
P    550 W 

  cos  1 SC   cos    1     68.0

 V SC I SC    1130 V 1.30 A  

Z  R  jX  869 68   326  j 806
EQ EQ EQ
The resulting per-unit impedances are
326  806 
R EQ   0.041 pu X EQ   0.101 pu
8,000  8,000 

The per-unit equivalent circuit is
I P I S
jX EQ
R EQ

+ 0.041 j0.101 +

V P R C jX M V S

80.3 j26.7

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