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Recent content by Jieve

  1. Jieve

    Evaporation from Tank (Theory Question)

    Assume I have an enclosure, say 4ft x 3ft x 3ft which is closed but not completely airtight. There is a small cylindrical tank of ethanol, say 1.5ft D x 1ft H, with a 1.5 inch pipe sticking out the top, open to the atmosphere (enclosure space). The liquid ethanol level in the tank is about 8”...
  2. Jieve

    PMDC Motor Model with Friction

    I'm trying to model a PMDC motor using manufacturer data and curves. What seems like it should be relatively simple is not adding up, and I'm hoping someone can tell me where I'm going wrong. I've got the no load speed and the rated speed / rated load torque from the manufacturer. From these two...
  3. Jieve

    VFD Line Reactor Saturation

    Thank you for the responses. I see. So there is still some reactance, but suddenly a small fraction of the original reactance once the current hits a certain magnitude? The waveform images are very useful, and that makes sense. I do have a 3-phase line reactor on a pump in an R&D lab where...
  4. Jieve

    VFD Line Reactor Saturation

    Some VFD manufacturers provide rated current and saturation current as rms values in the datasheets of their line reactors. VFD input current is, however, not a clean sinusoid, but rather a series of current pulses (4 per cycle with 3-phase input, 2 per cycle with 1-phase input) with peaks that...
  5. Jieve

    VFD Power Conservation

    For the case where I calculated displacement power factor using the equation in the link that you responded to, I used a fluke 87V multimeter directly measuring input current, then as a sanity check on the rms current value, I used a Fluke i30s clamp with oscilloscope, exported the data from the...
  6. Jieve

    VFD Power Conservation

    The formula was taken from this post on electronics stack exchange describing how modern power meters calculate power factor with non-linear loads: https://electronics.stackexchange.com/questions/49964/calculating-the-true-power-factor-in-non-linear-loads Do you disagree with the responses?
  7. Jieve

    VFD Power Conservation

    Interesting read, will dig deeper into the difference power factor types ... none of the sources I have come across have specified this; nor in the white paper I linked. Although the white paper says this "This means that the ratio of kW/kVA defined as “power factor” will be improved" I used a...
  8. Jieve

    VFD Power Conservation

    Coming back to this as I’ve been taking additional measurements and thinking about the responses here. VFDs are generally said to be power factor correctors with very high input power factors, almost at unity. Taking data from some scope measurements of VFD input voltage and current with...
  9. Jieve

    VFD Power Conservation

    In a textbook I have here, "Fundamentals of Electric Circuits, 4th Ed" by Alexander and Sadiku, Chapter 11 discusses AC Power Analysis, with Chapter 11.7 entitled "Conservation of AC Power". In this section it discusses any network of various load impedances powered by an AC source and states...
  10. Jieve

    VFD Power Conservation

    In the 3-phase rectified case you're correct about the voltage not really being oscillatory, in the 1-phase case though the voltage is a rectified single-phase sine wave so it is quite oscillatory. But you're correct about the reactive power in this VFD example; I was writing that thinking about...
  11. Jieve

    VFD Power Conservation

    Well I appreciate you chiming in and giving your input and spuring me to think about it more deeply. All correct. From my understanding, the reactive power at the output is just a result of the phase shift due to motor inductance when the IGBTs switch to generate the PWM voltage waveform. But...
  12. Jieve

    VFD Power Conservation

    While I'm not familiar with STATCOMs, from a quick google search it seems that they have DC bus storage caps similar to a VFD. The energy to create the reactive power comes from the energy stored in the capacitors. So it's not out of thin air. And a particular DC bus cannot simply supply...
  13. Jieve

    VFD Power Conservation

    Right, they can source reactive power as part of the conversion process, but energy still needs to be conserved; that reactive power cannot come out of thin air. In my example above, the output VA is about 2.5x the input, that's the piece I seem to be missing.
  14. Jieve

    VFD Power Conservation

    The motor power factor at full load is 0.9, giving sin(phi) = 0.4358, x FLA of 4.8 = 2.09A (magnetizing, unloaded current) which is pretty much exactly what the panel is reading. Do you mean input current? The output is pretty sinusoidal (albeit noisy), the input definitely is not. Which is...
  15. Jieve

    VFD Power Conservation

    So what you're saying is that real power is conserved but complex power is not. Which is not the case for a transformer, for example, where complex power is conserved. While not doing useful work, energy is still stored in inductors and capacitors, and must be conserved. So that doesn't quite...
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