Mesh analysis with supply phase angle

Discussion in 'Homework Help' started by Raikiri, Aug 11, 2009.

  1. Raikiri

    Thread Starter Member

    Mar 22, 2009
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    Hi, urgently need help as I have an exam tomorrow and I'm unsure of this type of question.

    The question asks you to find the three mesh currents in a circuit that only has resistors and power supplies and write down the simultaneous equations in matrix form. In the question there are two power supplies and say for example they were 6V and 4V then two of the equations would equal 6 and 4 yes?

    Well I understand that much but what would I write instead of 6 if the voltage was 6V with a phase angle of 30???

    -------
    the above is my main question but if anyone has the time to explain how I would find the ACTUAL currents after this step and also how I would do the question if I was given 2j ohms for a value of a resistor?

    THANKS!!
     
  2. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,157
    Post the circuit and your attempt at solving the circuit.

    2j ohms is not a resistor.
     
  3. Raikiri

    Thread Starter Member

    Mar 22, 2009
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    I've attached the pdf, its Q1.

    2I1 - I2 = 6
    3I2 - I1 - I3 = 0
    2I3 - I2 = 4?

    I'm asking is it right to have 4 there since its 4 with a phase angle of 30 deg?
     
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  4. Raikiri

    Thread Starter Member

    Mar 22, 2009
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    anyone? I really need help on this part asap, how does a voltage supply with a phase angle affect things? Should I just use 4V???
     
  5. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Since the voltage source in question has a phase angle associated with it, you should include the effect of that angle throughout the analysis.

    hgmjr
     
  6. Raikiri

    Thread Starter Member

    Mar 22, 2009
    16
    0
    I had a previous question where the resitors had complex number values 1+j1 ohms and 2+2j ohms, how would I do that?
     
  7. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
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    the j operator indicates reactance while the first number is impedance.

    your professor may have used a resistor symbol, but to get reactance, there must be capacitance, inductance, or a combination of both.

    1+j1 ohms shows a complex circuit having an impedance of 1 ohm with an inductive reactance of 1 ohm. 1 -j1 would be 1 ohm impedance with capacitive reactance of 1 ohm.

    visit http://www.allaboutcircuits.com/vol_2/chpt_2/5.html for more details.
     
  8. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    2,281
    326
    The last equation becomes (watch out for the proper sign):

    2I3 - I2 = -4<30°

    or

    2I3 - I2 = -3.4641 - j2

    Then you solve the simultaneous equations the usual way, but doing complex arithmetic throughout.
     
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