Page 237 - Solutions Manual to accompany Electric Machinery Fundamentals

ylabel('\bf\itn_{m} \rm\bf(r/min)');
title ('\bfSeries DC Motor Torque-Speed Characteristic');
grid on;
hold off;

The resulting torque-speed characteristic is shown below:

8-14. A 20-hp 240-V 76-A 900 r/min series motor has a field winding of 33 turns per pole. Its armature
resistance is 0.09 , and its field resistance is 0.06 . The magnetization curve expressed in terms of
magnetomotive force versus E at 900 r/min is given by the following table:
A
E , V 95 150 188 212 229 243
A

F, A turns 500 1000 1500 2000 2500 3000
Armature reaction is negligible in this machine.
(a) Compute the motor’s torque, speed, and output power at 33, 67, 100, and 133 percent of full-load
armature current. (Neglect rotational losses.)
(b) Plot the terminal characteristic of this machine.

Note: An electronic version of this magnetization curve can be found in file
prob8_14_mag.dat, which can be used with MATLAB programs. Column
1 contains magnetomotive force in ampere-turns, and column 2 contains the
internal generated voltage E A in volts.
SOLUTION Note that this magnetization curve has been stored in a file called prob8_14_mag.dat. The
first column of the file is an array of mmf_values, and the second column is an array of ea_values.
These values are valid at a speed n o = 900 r/min. Because the data in the file is relatively sparse, it is
important that interpolation be done using smooth curves, so be sure to specify the 'spline' option in
the MATLAB interp1 function:

load prob8_14_mag.dat;

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