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Unity power factor ?

  1. Jan 12, 2012 #1

    iam wondering about the unity power factor ..

    for example if we have a motor that will cause the power factor to be lagging by 0.3

    what will happen if we add capacitor to make the power factor 1 (unity)

    now we will not have any reactive power and we reduced the current to the minimum so that real power will equal the apparent power.

    will that affect the motor ?
  2. jcsd
  3. Jan 12, 2012 #2
    It will not affect the motor at all. The motor cannot even determine whether the capacitor is present.
  4. Jan 19, 2012 #3
    Unity pf will affect the current and thereby the losses in the circuit feeding your motor. If this losses are significant they will sag the voltage feeding your motor. In rare conditions this lower voltage could adversly affect your motor.
    For example, I have a two speed motor with 11kW rated output at pf near to 1. The same
    motor can be used at half speed 7KW output but with a reduced pf of only 0.68.
    By compensating the lousy pf I am able to run this motor on a 380V 3phase 25A supply. instead of the otherwise required 35A. Since in my country there is a huge difference
    in electricity base price delivered to 25A mainfuses compared to 35A (hundreds of $ per year) it makes sense to compensate. Under other conditions things may be different.
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