1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Calculating Input Voltage of a Step Down Transformer

  1. Mar 1, 2017 #1
    1. The problem statement, all variables and given/known data
    A pair of power transmission lines each have 0.68-Ω resistance and carry 650 Amp. If the primary voltage of the 10:1 step-up transformer is 4.6 kV, calculate the input voltage of the step-down transformer at the other end.

    2. Relevant equations
    P=IV
    V=IR
    IpVp = IsVs

    3. The attempt at a solution
    I recognized that when the current passes through the primary transformer it will increase, so I used V = IR and rearranged to I = V/R = (4600)/(2(0.68)) = 3382.35A I don't know how to proceed afterwards because if I try to solve for voltage I receive 4600 which is equal to the primary transformer, and cannot be the case because this is a step down transformer.
     
  2. jcsd
  3. Mar 1, 2017 #2

    kuruman

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    You have not used the given 10:1 step up ratio.
     
  4. Mar 1, 2017 #3
    So you mean to tell me that the primary transformer has 10 turns and the secondary has 1 turn? In that case would I use Vs/Vp = Ns/Np? Manipulate for Vs and then solve?
     
  5. Mar 1, 2017 #4

    kuruman

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    I mean to tell you that there are two transformers. Read the problem carefully
    There is a 10:1 step up transformer at one end of the transmission line and a step down transformer at the other end connected to the load.
     
  6. Mar 1, 2017 #5
    Okay, this is what I have come up with. The voltage is stepped up from the first transformer therefore, the current is stepped down. I calculate the secondary current by using Is/Ip=Np/Ns and I end up getting 65A. To find the input voltage in the second transformer I simply used V=IR noting that R = 2(.68), and I end up with an input voltage of 88.4 Volts
     
  7. Mar 1, 2017 #6

    kuruman

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Is this the current in the transmission lines? The problem states that the transmission lines carry 650 A. Consider finding how much power is lost in the course of transmission. Subtract that from the power going in and that is the power that reaches the step down transformer at the other end.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Calculating Input Voltage of a Step Down Transformer
Loading...