Page 189 - Solutions Manual to accompany Electric Machinery Fundamentals

% Plot the torque-speed curve
figure(1);
plot( nm,t_ind,'b-','LineWidth',2.0);
xl abel('\bf\itn_{m}');
ylabel('\bf\tau_{ind}');
title ('\bfI nduction Motor Torque-Speed Characteristic');
grid on;
The resulting plot is shown below:

The starting torque of this motor is about 17.9 N m .

6-23. A 460-V four-pole 75-hp 60-Hz Y-connected three-phase induction motor develops its full-load induced
torque at 3.5 percent slip when operating at 60 Hz and 460 V. The per-phase circuit model impedances of
the motor are
R = 0.058  X = 18 
1
M
X = 0.32  X = 0.386 
2
1
Mechanic al, core, and stray losses may be neg lected in this problem.
(a) Find the value of the rotor resistance R 2 .

(b) Find  max , s max , and the rotor speed at maximum torque for this motor.
(c) Find the starting torque of this motor.

(d) What code letter factor should be assigned to this motor?
SOLUTION The equivalent circuit for this motor is

183