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Why armature MMF is triangular in waveform?

  1. Jun 23, 2017 #1
    Why armature mmf is triangular in waveform? According to Faraday's law, the mmf should be rectangular. But I read some where that the total mmf of all the coils sums up to produce triangular waveform. I don't understand how that happen.
     
  2. jcsd
  3. Jun 28, 2017 #2
    Thanks for the thread! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post? The more details the better.
     
  4. Jun 28, 2017 #3

    jim hardy

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    Without knowing what that author was describing , how would anybody venture even a guess ?

    What kind of machine is it you describe that has triangular armature mmf ?
     
  5. Jul 7, 2017 #4
    Sorry about that. I am asking for a DC machine.
     
  6. Jul 7, 2017 #5

    jim hardy

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    The phrase "Triangular Armature MMF" makes no sense to me

    Armature MMF in a DC machine adds (by vectors) to the field MMF , shifting it off axis. It's not time variant unless armature current is also time variant.

    I can't fathom what your author had in mind.

    Got a picture from his book ?

    Sorry,

    old jim
     
  7. Jul 8, 2017 #6

    cnh1995

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    I think he's talking about this.
    Armature-Reaction1.jpg
     
  8. Jul 8, 2017 #7

    jim hardy

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    Ahhh uniform air gap,
    that step wave says it all,
    each step includes another armature turn
    smooth out the steps and you have your triangle wave.

    I never thought of it that way.

    Picture is worth a thousand words again ?

    thanks cnh !

    here's another picture
    use your right hand rule (my 'hand' came out a bit small)
    armature_reaction.jpg
     
  9. Jul 16, 2017 #8
    "
    "
    What does this line means?
     
  10. Jul 16, 2017 #9
    Can you please explain how step wave is obtained due to uniform air gap?

    Also, I am really sorry to take your time but I didn't understand what the above picture wants to say.
     
  11. Jul 16, 2017 #10

    jim hardy

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    a picture is worth a thousand words..

    armaturemmftriangle.jpg

    The steps i took as author's attempt to convey idea that total mmf is sum of mmf's from alll the individual conductors.

    I was taught to regard armature current as a sheet so just drew one vector for MMF.

    So to me this was a new idea. Old guys don't handle new ideas so well as you younger folks with your more facile brains.

    old jim
     
  12. Jul 16, 2017 #11
    I applied right hand rule on the pair of conductors as you showed and the direction of flux was downwards. I still don't understand how it forms a step wave.
     
  13. Jul 16, 2017 #12
    I am not able to imagine how this thing will look like.
     
  14. Jul 16, 2017 #13

    jim hardy

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    Conventional or electron current ?

    Big Ten-OOPS !


    righthandrule.jpg
     
    Last edited: Jul 16, 2017
  15. Jul 16, 2017 #14
    Conventional current.
     
  16. Jul 16, 2017 #15
    In this image, the cross represents outward electron current and inward conventional current. Am I right?
     
  17. Jul 16, 2017 #16

    jim hardy

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    You're right i drew 'em backwards ! Will fix it

    i knew something was upside down...
     
  18. Jul 16, 2017 #17

    jim hardy

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    righthandrule2.jpg

    I'm not sure what author is portraying there.
    At first glance it looks as if he may have drawn mmf upside down too,

    What's known is mmf's add up. I think that's what he is attempting to convey.
     
    Last edited: Jul 16, 2017
  19. Jul 16, 2017 #18
    The author is smoothing/adding the step waves to obtain the triangular wave as you said in one of the comments. But how the step wave is obtained on the first place? I am not able to figure this out.
     
  20. Jul 17, 2017 #19

    jim hardy

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    Every amp-turn adds its MMF to the total.
    Every conductor is the boundary of a current loop carrying some number of amp-turns.
    So at each conductor is an increment in MMF., or a decrement depending which direction you are traversing, equal to the amp-turns in that loop.
    That his steps are all the same size suggests the condustors he showed are in series.
     
    Last edited: Jul 17, 2017
  21. Jul 23, 2017 #20
    This is informative. But I got one more doubt here. According to this picture ,
    upload_2017-7-23_19-49-55.png
    The MMF should increase in direction of red to light violet, but the armature MMF is shown to be decreasing. please correct me where my understanding is going wrong.
     
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