Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: 2 Port Network

  1. Jul 25, 2011 #1
    http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-061-introduction-to-electric-power-systems-spring-2007/assignments/ps1ans.pdf [Broken]
    Problem #3

    Where do the minus signs come from in the admittance matrix?

    also, there is this statement
    "Thus it is clear that R3 = 1/3 and"
    and later the statement
    "R12 = R3 =1"



    2. Relevant equations



    3. The attempt at a solution

    From what I think it would be that the T circiut would be 1ohm for all three resistors, but that isnt what the solution is.
    Can someone help me please understand?
    thank you for your time and have a good day
     
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Jul 25, 2011 #2

    gneill

    User Avatar

    Staff: Mentor

    The negative values in the admittance matrix are there because of the definitions of the current and voltage directions that define the ports. Port currents are always taken to be INTO the port terminal (and out of the return path for the given port).

    attachment.php?attachmentid=37523&stc=1&d=1311640759.gif

    Regarding the "R3 = 1 or R3 = 1/3" question, it would appear that there is a mistake in the question document; the author took the value from the matrix as written, but failed to multiply by the constant 1/3 that was factored out of the matrix.
     

    Attached Files:

  4. Jul 26, 2011 #3
    thank you for your help
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook