Response of AC motor to frequency change?

I was wondering about this AC motor scenario:

You have an AC motor with some constant rms voltage applied at 60Hz. The motor is moving some load, so its stable at some rpm and torque.Now you increase the frequency of the applied voltage but not its rms magnitude. What would happen? Increasing the frequency would make the stator's magnetic field spin around more quickly, but what effect, if any, would that have on the rotor/load?

3 Answers

  • 5 months ago
    Favorite Answer

    Simple answer:

    Motor windings have impedance which 

    is the vector sum of inductive reactance

    and resistance. Increasing frequency drops Voltage while increasing speed and 

    load. The consequence is similar to brown out with current increasing to locked rotor.

  • 5 months ago

    The motor Data sheet will tell you the operating Frequency Range to meet specs. If you lower the operating frequency the motor will get hotter and run slower.

  • qrk
    Lv 7
    5 months ago

    Free-running motor rpm is dictated by the frequency of the supply voltage. Increase the frequency and the shaft turns faster. If you go too low in frequency, you'll start to run in to saturation issues and over heat the motor.

Still have questions? Get your answers by asking now.