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# Re: [femm] Inductances in electrical transformers

- To: femm@yahoogroups.com
- Subject: Re: [femm] Inductances in electrical transformers
- From: Keith Gregory <k.gregory@lboro.ac.uk>
- Date: Mon, 25 Nov 2002 08:52:03 +0000
- In-reply-to: <002a01c29401$f71ac4c0$db272dd5@tin.it>

`Fabio,`
`Just a suggestion but if you are setting the primary current to 10A (equivalent to 45.45 mA) and you have a turns ratio of 220/117 then try setting the secondary current to 10x220/117 =18.8A (equivalent to 160.7mA) and see what happens.`
`In addition, I am not clear as to why you would want an air-gap. In a voltage transformer it would just increase the losses.`
`Keith.`
`At 22:39 24/11/2002 +0100, you wrote:`

>     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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  - Inductances in electrical transformers
    - From: "Fabius" <xfabius@email.it>

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