Page 234 - Solutions Manual to accompany Electric Machinery Fundamentals
P. 234

(a)  What is the efficiency of the motor at full load?
                     (b)  What are the speed and efficiency of the motor if it is operating at an armature current of 40 A?

                     (c)  Plot the torque-speed characteristic for this motor.

                      Note:   An  electronic  version of this magnetization curve can be found in file
                              p85_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)  The output power of this motor at full load is

                               P   7.5 hp 746 W/hp       5595 W
                          OUT
                 The input power is
                         P   V I   120 V 56 A  6720 W
                          IN   T  L
                 Therefore the efficiency is


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