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# Inductances in electrical transformers

- To: <femm@yahoogroups.com>
- Subject: Inductances in electrical transformers
- From: "Fabius" <xfabius@email.it>
- Date: Sun, 24 Nov 2002 22:39:27 +0100

    Hi all.
    I am trying to calculate mutual and leakage inductances in single phase
    trasformer as in attached file.
    I have modeled this transformer with core EI having a cross section of 50x80
    mm, 220 turns at the primary and 117 turns at secondary.
    The core extends 0.08m in the into-the-page direction.
    I also added a small gap between E and I to be sure that there is no
    relevant saturation.
    First i evaluated the self inductance Ls1 = 290.6mH and Ls2 = 82.2 mH using
    A,J integral as explained in tutorial.
    I set primary windings to circuit primary+ and primary- having + or - 10A,
    so the current I1 is 10/220 = 45.45 mA
    Then i turned off primary winding and set secondary to a circiut carring 10
    A.
    Theese results are in according with the classical formulas.

    Then i evaluated mutual inductance as described in Femm manual at
    page 34. N2= 117 , I1=10/220 , a2 = 1.139E-3 m², integ A1dV2 = 4.339E-7 but
    the result was M = 77.1 mH
    ( i multiplied the integ x 0.08 , the 3 dimension of core )
    So the cooupling factor k = M / sqr(L1*L2) = 0.498

    that is wrong. ( I think k is near 1 )

    What is wrong in this model ?
    Can someone help me ?
    Best regards
    Fabio

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