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Very simple per unit question

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  1. Nov 9, 2015 #1
    If you took: VBase / ZBase

    does that give you IActual

    or IBase or what?

    Because it seemed to give me IActual.

    Cheers
     
  2. jcsd
  3. Nov 10, 2015 #2

    Simon Bridge

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    What is the difference?
     
  4. Nov 10, 2015 #3
    Like if Iactual = Ibase*Iper unit
     
  5. Nov 10, 2015 #4

    Simon Bridge

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    OK... so do that for the other "base" units.
    Remember what the base and per unit parts mean.
    What is the relationship between actual things?
     
  6. Nov 10, 2015 #5
    Well I know that Vbase / Zbase = (Vactual/Vpu) / (Zactual/Zpu)
    =Vactual * Zpu / Vpu*Zactual = Iactual * (Zpu/Zactual)
    But I'm not sure what that means for the last part of the last term
     
  7. Nov 10, 2015 #6
    Sorry, the final term is wrong here:

    Ibase=Vbase / Zbase = (Vactual/Vpu) / (Zactual/Zpu) =Vactual * Zpu / (Vpu*Zactual) = Iactual * (Zpu/Vpu)

    Iactual * (Zpu/Vpu)=Iactual*Ipu
     
  8. Nov 10, 2015 #7
    Oh right.
    but Isn't (Zpu/Vpu) = 1 / Ipu

    so Vbase / Zbase = Iactual / Ipu ?



    Also, side question, say you were given the rated power and voltage for a system, so then you can work out the rated base impedance. But does that mean that
    Ibase = √(Sbase - Zbase) ?
     
  9. Nov 12, 2015 #8
    Sorry again. My mistake, this time : Vbase / Zbase = Iactual / Ipu, indeed.

    Also for single phase system Ibase=sqrt(Sbase/Zbase) .So, what further?
     
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