Page 42 - Solutions Manual to accompany Electric Machinery Fundamentals

The magnetization current is 5.5134% of full-load current.
The rms magnetization current is 0.230 A. Since the full-load current is 1000 VA / 240 V = 4.17 A, the
magnetization current is 5.51% of the full-load current. The resulting plot is

(c) The magnetization current is a higher percentage of the full-load current for the 50 Hz case than for
the 60 Hz case. This is true because the peak flux is higher for the 50 Hz waveform, driving the core
further into saturation.

2-6. A 1000-VA 230/115-V transformer has been tested to determine its equivalent circuit. The results of the
tests are shown below.
Open-circuit test Short-circuit test
(on secondary side) (on primary side)
V OC = 115 V V SC = 17.1 V
I OC = 0.11 A I SC = 8.7 A
P OC = 3.9 W P SC = 38.1 W
(a) Find the equivalent circuit of this transformer referred to the low-voltage side of the transformer.
(b) Find the transformer’s voltage regulation at rated conditions and (1) 0.8 PF lagging, (2) 1.0 PF, (3)
0.8 PF leading.
(c) Determine the transformer’s efficiency at rated conditions and 0.8 PF lagging.

SOLUTION
(a) OPEN CIRCUIT TEST (referred to the low-voltage or secondary side):

0.11 A
Y  G  jB   0.0009565 S
C
M
EX
115 V
P 3.9 W
  cos  1 OC  cos  1  72.0

VI  115 V 0.11 A 
OC OC
Y EX  G  C jB  M 0.0009565   72 S   0.0002956  j 0.0009096 S
1
R   3383 
C
G
C
1
X   1099 
M
B
M
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