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Trigonometry on a transformer

  1. Apr 22, 2014 #1
    On a trafo i just bought, it says COS Ø = 0,99. What does this mean?
    Is there some angle involved in changing the voltage?
  2. jcsd
  3. Apr 22, 2014 #2


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    That is the 'Power factor'. To be simple, the ratio of actual power consumed to the product of voltage and current through the trafo is 0.99, it means.
    See this:
    Last edited: Apr 22, 2014
  4. Apr 22, 2014 #3


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  5. Apr 22, 2014 #4

    jim hardy

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    trafo ?


    To your trig question:

    cos-1(0.99) = 8.1 degrees
    and that's the angle between primary side volts and amps at rated resistive load.

    draw a right triangle with a hypotenuse of 1, base of 0.99 and an opposite side of 0.1424
    this represents primary current at rated conditions with resistive load
    small angle is 8.1 degrees
    base is 0.99 units and is load current corrected for turns ratio
    opposite side is 0.1424 units and is magnetizing current
    hypotenuse is total current flowing into primary

    so this transformer draws 14.24% magnetizing current.
    Last edited: Apr 22, 2014
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