Phasor addition

Discussion in 'Homework Help' started by JimmyB, Jun 19, 2010.

  1. JimmyB

    Thread Starter Member

    Jun 1, 2010
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    Hi is anyone able to help me with this question??

    draw to scale 3 phasors representing the following voltages, taking e1 as reference phasor

    e1:= 80 sin ωt volts

    e2= 60 cos ωt volts

    e3 = 100 sin (ωt-∏/3) volts

    I think i understand this part, is it 1 sin wave and 1 cosine wave and 1 lagging sin wave on one 2∏ cycle chart,

    the part im not sure is it then asks to sum these 3 voltages and express it in the form Em sin (ωt ± θ), i think i can sum the 2 sin waves though i'm unsure, it is the cosine i'm unsure with...

    is anyone able to help please

    jim
     
    Last edited: Jun 20, 2010
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Consider the phasor e2 cosine as leading the reference e1 sine phasor by 90° [∏/2 radians]. You've typed e2 twice but I assume the 3rd phasor is e3. Phasor e3 lags e1 by ∏/3 [60°].

    Use phasor addition to find the sum e1+e2+e3

    e_{tot}=e_{1}+e_{2}+e_{3}=80\angle 0^{o}+60\angle 90^{o}+100\angle -60^{o}

    Then convert the resultant phasor back to the time-domain equivalent.
     
    Last edited: Jun 19, 2010
  3. JimmyB

    Thread Starter Member

    Jun 1, 2010
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    sorry it was ment to be e3.. edited now...

    Thanks tnk, does that mean convert into rectangular add the votages then back into polar form..

    Am I right about the drawing?? all 3 waves are drawn on one 2∏ cycle..

    thanks

    jim
     
  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    If you are lucky enough to have a calculator that will do everything (including addition) in polar form then no - you don't have to convert. Otherwise you will probably have to go to rectangular form to do the addition and then back to polar.

    Are you sure you know what a phasor diagram is? I'm not sure of your meaning in - "all 3 waves on a 2∏ cycle". You may be thinking of the time based waveform diagram - which is not a phasor diagram.
     
  5. JimmyB

    Thread Starter Member

    Jun 1, 2010
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    are Phasor diagrams straight lines?

    or can I draw 2 sin waves and 1 cosine wave superimposed on one graph..

    If they are staright lines do i have e1 horizontal mag 80, e2 same origin but vertical mag 60, e3 same origin mag 100 -60° from e1.. is that what is ment by phasor diagram.. or should e2 start from the end of e1, and e3 start from the end of e2.. I know that is what you should do to add the phasors..

    thanks

    jim
     
    Last edited: Jun 20, 2010
  6. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Something like this .....
     
  7. JimmyB

    Thread Starter Member

    Jun 1, 2010
    38
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    Thanks tnk
     
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