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Power Factor and Phasor Diagram

  1. Aug 19, 2010 #1
    OK, Hello!

    Have to make sure as I felt like I knew my stuff but failed my first exam, am I on the right tracks?

    Power Factor = Cosine of phase angle

    Phase angle = Tan Inverse ((XL-Xc)/R)

    (So you know)
    XL= Inductive Reactance
    Xc= Capacitive Reactance
    R = Resisstance

    Am I right so far?

    And for the phasor diagram, since in this case XL > Xc it would be illustrated as a horizontal line going towards the right, marked as Voltage, and a second line would go from the origin of the Voltage line downwards at an angle which would be the Phase angle, this second line illustrating the Current. Is that all I would have to do if I was told to draw a phasor diagram?

    Is all this correct? My confidence has been wounded :(,,!!! I must make sure!!!, so please help if you can!
  2. jcsd
  3. Aug 19, 2010 #2


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    Gold Member

    Those equations are correct, even if they do look a little different from the standard ones.

    Generally reactances sum to give a total reactance, so the outcome is either a capacitive system or an inductive system, rather than saying that there is more inductance than capacitance. Same result though.

    If you aren't given numbers, then that phasor diagram would be accurate.

    It may also help to keep the acronym 'CIVIL' in mind, as per the diagram attached.

    Attached Files:

  4. Aug 20, 2010 #3
    Thank you Zryn. Nice to know I'm on the right tracks. Will remember CIVIL, it will be very useful. And will also bare in mind about inductive and capacitive circuits. I'm sure if I knew the basics about Xc and XL circuits that what you said would be obvious so will have to work on that.
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