1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

To find power factor of the ac circuit given only the source and load voltages

  1. Feb 12, 2012 #1
    how to find power factor of the load, the three voltmeter readings are V1=220v,V2=122v,V3=136v
     

    Attached Files:

    • pf.JPG
      pf.JPG
      File size:
      5.1 KB
      Views:
      185
  2. jcsd
  3. Feb 13, 2012 #2

    NascentOxygen

    User Avatar

    Staff: Mentor

    Start with the vector sum of two of these voltages equalling the third, and determine the triangle representing this.
     
  4. Feb 13, 2012 #3
    The load must be a combination of resistance,R, and reactance,X, because 220^2 does not equal 122^2 + 136^2
    this means that for the load Vr^2 + Vx^2 = 136^2
    this will give 2 equations which can be solved for the Vr in the load and the Vx for the load
     
  5. Feb 13, 2012 #4

    NascentOxygen

    User Avatar

    Staff: Mentor

    No calculations are needed beyond what I outlined:
     
  6. Feb 13, 2012 #5
    Some calculation is needed to get a value for Cosθ, either from a vector diagram or by algebra.
    Does anyone have an answer? I got 0.83. Purely for personal preference I took the reactive part of the load to be inductive but it could have been capacitative.
     
  7. Feb 14, 2012 #6

    NascentOxygen

    User Avatar

    Staff: Mentor

    I get pf=0.453
     
  8. Feb 15, 2012 #7
    NascentO
    Here is what I did, I interpreted the question as asking for the power factor for the load connected to the supply voltage of 220V (this is what is usually meant for power factor).
    The question however does say 'the load' and 'the load' is clearly marked onthe diagram.
    I would say there are 2 correct answers !!!
    Sorry!! attachment not there.... I will do it again
     
    Last edited: Feb 15, 2012
  9. Feb 15, 2012 #8
    Attachment for power factor calculation
     

    Attached Files:

  10. Feb 15, 2012 #9

    NascentOxygen

    User Avatar

    Staff: Mentor

    I interpreted it as a lossy transmission line. Otherwise, I agree with your answers.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook