A 100-kW, three-phase, 60-Hz, 460-V, six-pole wound-rotor induction motor develops its rated full-load output at a speed of 1158 r/min when operated at rated voltage and frequency with its slip rings short-circuited. The maximum torque it can develop at rated voltage and frequency is 310 percent of full-load torque. The resistance of the rotor winding is 0.17 O/phase Y; neglect any effects of rotational and stray-load loss and stator resistance.
a. Compute the rotor I2R loss at full load.
b. Compute the speed at maximum torque in r/min.
c. How much resistance must be inserted in series with the rotor windings to produce maximum starting torque? With the rotor windings short-circuited, the motor is now run from a 50-Hz supply with the applied voltage adjusted so that the air-gap flux wave is essentially equal to that at rated 60 Hz operation.
d. Compute the 50-Hz applied voltage.
e. Compute the speed at which the motor will develop a torque equal to its rated 60-Hz value with its slip-tings shorted.