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Thread: Power factor

  1. #311
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    Again, we are now arguing terminology.

    If you consider _instantaneous_ power, then you have _watts_ flowing into the capacitor for 1/4 cycle, and then _watts_ flowing out of the capacitor for 1/4 cycle. Considering _instantaneous_ measurements watts and volt amperes are _equivalent_.

    It is only when you are looking at time average measurements, averaged over entire half cycles, that it is meaningful to consider W and VA as different things. But now we are talking about the terms W and VA.

    For time averaged measurements in ac systems, W describes (real) energy delivered to a load over time and VA describes (real) energy shuttling back and forth between source and load, with no net energy delivered. The energy shuttling between generator and capacitor is _real_ energy that could really do work, but instead gets swapped between the two components.

    -Jon

  2. #312
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    Quote Originally Posted by winnie View Post
    An inductor stores energy in a magnetic field, which requires current to flow.
    Typically, the dc coil of a relay or contactor will have a flywheel diode across it to allow the current to continue until the inductive energy is dissipated.
    Si hoc legere scis nimium eruditionis habes.

  3. #313
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    Quote Originally Posted by winnie View Post
    Again, we are now arguing terminology.

    If you consider _instantaneous_ power, then you have _watts_ flowing into the capacitor for 1/4 cycle, and then _watts_ flowing out of the capacitor for 1/4 cycle. Considering _instantaneous_ measurements watts and volt amperes are _equivalent_.

    It is only when you are looking at time average measurements, averaged over entire half cycles, that it is meaningful to consider W and VA as different things. But now we are talking about the terms W and VA.

    For time averaged measurements in ac systems, W describes (real) energy delivered to a load over time and VA describes (real) energy shuttling back and forth between source and load, with no net energy delivered. The energy shuttling between generator and capacitor is _real_ energy that could really do work, but instead gets swapped between the two components.

    -Jon
    Since the title of the thread is power factor, one might reasonably assume that it isn't about instantaneous values.
    Si hoc legere scis nimium eruditionis habes.

  4. #314
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    power factor can be both: instantaneous and average/fixed (but we already knew that)
    for grid load control instantaneous is required
    perhaps for a fixed load like a motor a constant is more appropriate

    the study of real time power factor is interesting

  5. #315
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    Quote Originally Posted by winnie View Post
    Again, we are now arguing terminology.

    If you consider _instantaneous_ power, then you have _watts_ flowing into the capacitor for 1/4 cycle, and then _watts_ flowing out of the capacitor for 1/4 cycle. Considering _instantaneous_ measurements watts and volt amperes are _equivalent_.
    Terminology to understand

    It is only when you are looking at time average measurements, averaged over entire half cycles, that it is meaningful to consider W and VA as different things. But now we are talking about the terms W and VA.

    For time averaged measurements in ac systems, W describes (real) energy delivered to a load over time and VA describes (real) energy shuttling back and forth between source and load, with no net energy delivered. The energy shuttling between generator and capacitor is _real_ energy that could really do work, but instead gets swapped between the two components.

    -Jon

    Perfect explanation

  6. #316
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    Quote Originally Posted by Besoeker View Post
    Since the title of the thread is power factor, one might reasonably assume that it isn't about instantaneous values.
    Perhaps, but in order to understand what PF is in the first place it helps to look at it milli second by millisecond. "phantom power" is a misnomer and often adds to the mystery of what happens in a capacitive or inductive circuit. There is no phantom power, only voltage and current.

  7. #317
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    Quote Originally Posted by Ingenieur View Post
    power factor can be both: instantaneous and average/fixed (but we already knew that)
    Did we???
    Si hoc legere scis nimium eruditionis habes.

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