Page 256 - Solutions Manual to accompany Electric Machinery Fundamentals

Note: An electronic version of this magnetization curve can be found in file
p87_mag.dat, which can be used with MATLAB programs. Column 1
contains field current in amps, and column 2 contains the internal generated
voltage E A in volts.

SOLUTION

(a) If the generator is operating with no load at 1800 r/min, then the terminal voltage will equal the
internal generated voltage E A . The maximum possible field current occurs when R adj = 0 . The
current is
V 120 V
I  F   6 A
R  F ,max F R adj 20   0 

From the magnetization curve, the voltage E at 1800 r/min is 135 V. Since the actual speed is 1800
Ao
r/min, the maximum no-load voltage is 135 V.
The minimum possible field current occurs when R = 40 . The current is
adj

V 120 V
I  F   2.0 A
R  F ,max F R adj 20   40 
From the magnetization curve, the voltage E at 1800 r/min is 79.5 V. Since the actual speed is 1800
Ao
r/min, the minimum no-load voltage is 79.5 V.

(b) The maximum voltage will occur at the highest current and speed, and the minimum voltage will
occur at the lowest current and speed. The maximum possible field current occurs when R = 0 . The
adj
current is

V 120 V
I  F   6 A
R  F ,max F R adj 20   0 

From the magnetization curve, the voltage E at 1800 r/min is 135 V. Since the actual speed is 2000
Ao
r/min, the maximum no-load voltage is
E A  n
E n
Ao o
n 2000 r/min
E  E   135 V  150 V
A
n o Ao 1800 r/min
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