Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Single Phase Induction motor winding phase difference

  1. May 12, 2017 #1
    So I'm trying to extract the electrical properties of a single phase induction motor. First off, how am I supposed to measure the phase difference between the start and run windings? I have L and R of start and run windings too!
    I have a torque vs slip curve up until 130% of rated load. Using this I was told I'm supposed to curve fit this data to the equation Torque*c1 = c2*s/(1+(j*w*t)) to get the time constant t of the rotor (or L/R of the rotor). I'm not sure how I'm supposed to do this. I also have this L/R value using the electrical model that I found with locked rotor measurements.
    If this system was to be switched with a capacitor to get 90 degrees phase shift, how do I calculate the capacitor value? I know I'm supposed to draw a phasor diagram and find the value of C so that it forms the required phase shift but I need more explication on that.
  2. jcsd
  3. May 12, 2017 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2017 Award

    For the phasor diagram. You should have a phasor pointing somewhere in quadrant I (up and to the right). Up is for the inductive portion, and horizontal is resistive portion. If you create a right triangle from this coming back down to the Real axis, this vertical leg coming down will be your capacitive phasor.

    Do you know how to calculate capacitive reactance from Capacitance and Frequency?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted