1. Wound-Rotor Motor

2. Torque-slip (speed) curves for a wound-rotor motor

3. Curve 3 – s=1
Curves 4, 5 – s>1
s>1 – “plugging” – reversal of a motor before it comes to rest by interchanging 2 of the 3 line leads going to the stator. nr is negative!

4. Example 5.10 page 198
A family of torque-speed curves for a y-connected, 400-hp, 2300-v, 14-pole, 60-Hz, wound-rotor induction motor is shown in Figure Curves A and D show the extremes of rheostat adjustment. Determine
a) the range of rotor speeds available by rheostat adjustment, assuming 100% rated torque load on the shaft:

5. Example 5.10 page 198 (continued)
b) the rheostat resistance required to obtain 260% rated torque when starting.
The ratio of stator turns per phase to rotor turns per phase is 3.8, and the motor parameters, in Ω/phase are R1=0.403, R2=0.317, X1=1.32, X2=1.32, XM=35.46.

6. Example 5.10 page 198 (continued)
Solution for part (a)
nr = ns(1-s)
Determine ns
ns = 120f/P = (120)(60)/14 = r/min
Look at the intersections of the curves with the 100% torque line
for the low-speed curve, D, s = 0.395
for the high-speed curve, A, s = 0.02

7. Torque-speed curves for Ex 5.10

8. Example 5.10 page 198 (continued)
for the low-speed case,
nr = ns(1-s) = ( ) = 311 r/min
for the high-speed case,
nr = ns(1-s) = (1-0.02) = 504 r/min

9. Torque-speed curves for Ex 5.10
260%

10. Example 5.10 page 198 (continued)
for part (b)
Curve B has locked-rotor torque of 260%
TDmax occurs at s = 0.74