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Homework Help: Single-phase transformer

  1. Feb 10, 2016 #1
    upload_2016-2-10_21-9-59.png upload_2016-2-10_21-9-59.png upload_2016-2-10_21-21-42.png upload_2016-2-10_21-21-42.png upload_2016-2-10_21-23-35.png upload_2016-2-10_21-23-35.png 1. The problem statement, all variables and given/known data

    I'm a bit thrown at this problem as I am unsure if firstly my equations so far are correct and secondly where/how I need to factor in the 50 Hz part. Or is this a red herring? Also, am I correct in thinking that the emf means voltage?

    Any help would be appreciated

    A single-phase transformer having a primary winding of 380 turns is connected to a 400 V, 50 Hz single phase supply.
    a the emf induced in the secondary winding of 100 turns;
    b the current in the secondary winding if the primary winding carries a current of 20 amperes;
    c the number of turns required in the secondary winding to produce an emf of 230 V.

    2. Relevant equations

    Vs = Ns x Vp / Np

    Vs = 100 x 400 / 380

    Is = Ip x Vp / Vs

    Is = 20 x 400 / 105.3

    Ns = Np x Vs / Vp

    Ns = 380 x 230 / 400

    3. The attempt at a solution
    a. = 105.3 V
    b. = 76A
    c. = 218.5
  2. jcsd
  3. Feb 10, 2016 #2


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    Hello Rhirhi, :welcome:

    What can I say ? To answer your questions:
    Equations are correct. You also apply them correctly and do the math correctly.
    The 50 Hz doesn't enter in the equations: you can assume the transformer is 'ideal' (no frequency dependence and no power loss).
    emf is indeed Voltage.

    In PF your part 3 doesn't really count as 'attempt at solution'; you just type the answers.
    But all in all: good work :smile: !
  4. Feb 10, 2016 #3
    Thanks very much BvU. you have put my mind at rest :-)
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