Frequency Calculation of a Wound Rotor Induction Motor
What is the frequency of the current on the rotor under different conditions for a 6 pole, 0.5 HP wound rotor induction motor in a 60 Hz system?
a. Resting.
b. The motor rotating at 500 r/min in the same direction as the rotating field.
c. The motor rotating at 500 r/min in the opposite direction to the rotating field.
d. The motor rotating at 2000 r/min in the same direction as the rotating field.
Answer:
a. The frequency of the rotor when the motor is resting is 60Hz. No emf is induced in the rotor winding.
b. The frequency of the rotor currents when the motor is rotating at 500 r/min in the same direction as the rotating field is 5.83Hz.
c. The frequency of the rotor currents when the motor is rotating at 500 r/min in the opposite direction to the rotating field is 17.5Hz.
d. The frequency of the rotor currents when the motor is rotating at 2000 r/min in the same direction as the rotating field is -6.67Hz.
Reflecting on the frequency calculation of a 6 pole, 0.5 HP wound rotor induction motor in a 60 Hz system reveals interesting insights. The frequency of the rotor currents varies depending on the rotor speed and direction of rotation relative to the rotating field of the stator.
When the motor is resting, the frequency of the rotor currents matches that of the stator, which is 60Hz. This occurs because there is no relative motion between the rotor and stator fields, resulting in no induced emf in the rotor winding.
As the motor rotates at different speeds and directions, the frequency of the rotor currents changes accordingly. When the motor rotates at 500 r/min in the same direction as the rotating field, the frequency is calculated to be 5.83Hz. Conversely, when rotating at the same speed but in the opposite direction, the frequency increases to 17.5Hz.
Interestingly, when the motor rotates at 2000 r/min in the same direction as the rotating field, the frequency of the rotor currents is determined to be -6.67Hz. This negative frequency indicates a reversal of current direction, highlighting the complex interplay between rotor speed and field rotation.