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    #16
    Originally posted by Besoeker View Post
    However, I do think you should correct the last paragraph

    No need. It is correct as written.
    Originally posted by Besoeker View Post
    As I'm sure you know, Joules/second is power in Watts.

    Not quite true. It is like the difference between saying “a dog is an animal” and “an animal is a dog.”

    A “Watt” is a “Joule per second,” but a “Joule per second” can be a “Watt” or it can be one of at least two other things. Specifically, a “Joule per second” could be a “Volt-Ampere Reactive,” which is a measure of reactive power, and a “Joule per second” could also be a “Volt-Ampere,” which is a measure of apparent power.
    Originally posted by Besoeker View Post
    There is no power associated with the vertical line. VArs are Wattless, thus can't be correctly expressed in terms of "joules of energy per second of time”.
    If you take each type of power down to the very fundamental units (i.e., length, mass, time, and charge), then,

    “Real Power” is measured in units of “Kilograms x (meters squared) / (seconds cubed)"
    “Reactive Power” is measured in units of “Kilograms x (meters squared) / (seconds cubed)"
    “Apparent Power” is measured in units of “Kilograms x (meters squared) / (seconds cubed)"
    Charles E. Beck, P.E., Seattle
    Comments based on 2017 NEC unless otherwise noted.

    Comment


      #17
      So you want to redefine the Joule?
      A Joule per second is a Watt which power, not apparent power.
      Take a reactive load like a capacitor.
      The current it takes times the applied voltage gives it's VA.
      Ignoring losses (a close approximation at power frequencies), there will be no power and thus no Watts. It will consume no Joules of energy in any one second period.
      In short, in an AC circuit, Joules per second is not VA.
      Si hoc legere scis nimium eruditionis habes.

      Comment


        #18
        Originally posted by Besoeker View Post
        It will consume no Joules of energy in any one second period.
        You missed the point. No one is saying that a Watt is the same as a Volt-Amp. When boiled down to their fundamental units of measure, both are quantified the same way. They are applied very differently, yes, but both have the same building blocks.

        The sentence you questioned in charlie b's dialog is correct as written. You are reading too much into it. Your points are valid, but you are correcting something that he didn't say.
        Engineers are always honest in matters of technology and human relationships. That's why it's a good idea to keep engineers away from customers, romantic interests, and anyone else who can't handle the truth.

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          #19
          Originally posted by drbond24 View Post
          The sentence you questioned in charlie b's dialog is correct as written)
          Since he is dealing with AC circuits, it is incorrect.
          VA and Watts are not the same thing except for the specific case of unity power factor.
          Specifically, a “Joule per second” could be a “Volt-Ampere Reactive,”
          That's just wrong.
          Si hoc legere scis nimium eruditionis habes.

          Comment


            #20
            Originally posted by Besoeker View Post
            VA and Watts are not the same thing except for the specific case of unity power factor.
            You're going to have to show me where he said "a VA and a Watt are the same thing." That is what you are arguing against, but that isn't what he said. Of course they are not the same thing.

            Break it down to fundamental units. Watts, VA, and VAr all break down to (kg*m^2) / (s^3).

            I think I would be correct in saying that the point here is that Watts, VA, and VAr all describe the same quantity of energy. They all describe different kinds of energy, of course, but not different amounts.

            Imagine you're on the USS Enterprise and you can convert mass and energy back and forth at your whim. You tell the computer to convert one Watt of energy into a mass. Then you tell the computer to convert one VA of energy into a mass. The computer will create you two identical masses.
            Engineers are always honest in matters of technology and human relationships. That's why it's a good idea to keep engineers away from customers, romantic interests, and anyone else who can't handle the truth.

            Comment


              #21
              Originally posted by Besoeker View Post
              So you want to redefine the Joule?
              A Joule per second is a Watt which power, not apparent power.
              Take a reactive load like a capacitor.
              The current it takes times the applied voltage gives it's VA.
              Ignoring losses (a close approximation at power frequencies), there will be no power and thus no Watts. It will consume no Joules of energy in any one second period.
              In short, in an AC circuit, Joules per second is not VA.
              In short...Joules per second could be VA, could be VAR, could be Watt. It depends on which of the three electrical components you are defining the product of current through and the voltage across.

              Electrical Engineers need to distinguish which type of Power we are talking about (Real, Reactive, Apparant), so we have come up with the VA, VAR, Watt units of measure. But we could also say Joules/sec inductive, Joules/sec capacitive, Joules/sec resistive.

              From my Physics and Circuits Textbooks:

              p = vi W

              for resistor p=Ri**2 W
              for inductor p=Li(di/dt) W
              for capacitor p=Cv(dv/dt) W

              Integration of the above equations results in the energy generated/absorbed by the device and its unit of measure is the Joule.


              We could also call it Beer Liquid, Beer Foam....but that's another story.
              Last edited by markstg; 06-10-09, 01:02 PM.

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                #22
                oppps, need to add Joules/sec total to account for all three type circuit elements.

                Comment


                  #23
                  Originally posted by Besoeker View Post
                  So you want to redefine the Joule?

                  I did no such thing, nor did I so much as attempt to do so.



                  Charles E. Beck, P.E., Seattle
                  Comments based on 2017 NEC unless otherwise noted.

                  Comment


                    #24
                    Originally posted by Besoeker View Post
                    VA and Watts are not the same thing except for the specific case of unity power factor.

                    Here again, I never said any such thing.
                    Originally posted by Besoeker View Post
                    Specifically, a “Joule per second” could be a “Volt-Ampere Reactive,” That's just wrong.

                    No it is not wrong. Real, Reactive, and Apparent Power all have the same fundamental units, and therefore they are given different names to allow us to more easily distinguish them.
                    Charles E. Beck, P.E., Seattle
                    Comments based on 2017 NEC unless otherwise noted.

                    Comment


                      #25
                      Quite right.
                      A Joule is not a measure of power. It is a unit of energy. One Watt second.
                      There are no Watts in the reactive component.
                      Si hoc legere scis nimium eruditionis habes.

                      Comment


                        #26
                        Originally posted by markstg View Post
                        In short...Joules per second could be VA, could be VAR, could be Watt. .
                        No. Just Watts.
                        Si hoc legere scis nimium eruditionis habes.

                        Comment


                          #27
                          Originally posted by Besoeker View Post
                          No. Just Watts.
                          Ok, glad you see it that an inductor or capacitor can absorb/generate watts.:smile:

                          Comment


                            #28
                            Originally posted by Besoeker View Post
                            A Joule is not a measure of power. It is a unit of energy. One Watt second.

                            A Joule is certainly equal to one watt-second. But it is not defined
                            Originally posted by Besoeker View Post
                            There are no Watts in the reactive component.



                            Do you have a response to the observation that two of us have made, to the effect that W, VA, and VAR have the same fundamental units (kilogram meter squared per second cubed)?
                            Charles E. Beck, P.E., Seattle
                            Comments based on 2017 NEC unless otherwise noted.

                            Comment


                              #29
                              Originally posted by charlie b View Post
                              A Joule is certainly equal to one watt-second. But it is not defined



                              Do you have a response to the observation that two of us have made, to the effect that W, VA, and VAR have the same fundamental units (kilogram meter squared per second cubed)?
                              Charlie, add me as a third.

                              Comment


                                #30
                                No, please don't stop. This is the best post I think I've ever read.

                                Thanks Charlie, I too have been in this buisness for 23 yrs and even though I've known the difference between watts, va, var, and pf I couldn't ever put the triangle thing together,(just never could see the relationship). So you have done in 5 minutes what 20+ yrs and all these books I own couldn't. Thanks a million.

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