A 35-kW, three-phase, 440-V, six-pole wound-rotor induction motor develops its rated full load output at a speed of 1169 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 245 percent of full load torque. The resistance of the rotor winding is 0.23r/phase Y. Neglect rotational and stray-load losses and stator resistance.

a. Compute the rotor 12R loss at full load.

b. Compute the speed at maximum torque.

c. How much resistance must be inserted in series with the rotor to produce maximum starting torque? The motor is now run from a 50-Hz supply with the applied voltage adjusted so that, for any given torque, the air-gap flux wave has the same amplitude as it does when operated 60 Hz at the same torque level.

d. Compute the 50-Hz applied voltage.

e. Compute the speed at which the motor will develop a torque equal to its rated value at 60-Hz with its slip tings short-circuited.