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Phasor transformation

Joe Bachi

Feb 3, 2013
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Feb 3, 2013
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Hey guys,
I attempted to solve the following exercise but i'm pretty sure i messed up somewhere because my answers just don't seem to add up
Can you please check my work?
Hope the pictures are clear enough
Photo Sep 21, 8 18 46 PM.jpg

Photo Sep 21, 8 18 58 PM.jpg
1) Express L, using R, C, and w so that R(equivalent) of AC is a pure resistor
2) Knowing that E(0)=180V, Find the amplitude of the main current I(0)
3) Find the amplitudes of U(AB) and U(BC)

Thank you in advance for your help :)
 

Harald Kapp

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Nov 17, 2011
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Your error is in the first line of computing the parallel circuit of R and C.
Two impedances in parallel are calculated as

1/Ztotal = 1/Z1 + 1/Z2 where Z1, Z2 are the impedances of the resistor and the capacitor.

The impedance of a capacitor is Zc = 1/jwC

Therefore:
1/Ztotal = 1/R + jwC

With that in mind, do your calculations again. If they still don't add up, show us the new results.
 

Joe Bachi

Feb 3, 2013
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Zc=1/jwC which is the equivalent to Zc=-j/Cw (by multiplying by j)
 

Laplace

Apr 4, 2010
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I arrived at the same expression for L as you did so you seem to be on the right track.
attachment.php
 

Attachments

  • MathCAD_L+RC.png
    MathCAD_L+RC.png
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Joe Bachi

Feb 3, 2013
21
Joined
Feb 3, 2013
Messages
21
I did the Fresnel representation of the circuit and my answers turned out to be the same, so i think it was right all along
Thank you all for taking the time to help :)
 
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