Leakage flux in Secondary winding?

Discussion in 'General Electronics Chat' started by Ammar Aziz, Aug 23, 2015.

  1. Ammar Aziz

    Thread Starter New Member

    Aug 23, 2015
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    Dear All, We know that in a transformer there is a bunch of flux (due to primary winding) that is not mutually coupled with the secondary winding. But how it is possible that there is a leakage flux (due to secondary winding) that is not mutually coupled with the primary winding, because secondary winding is not the cause of flux. Can you please suggest me that why textbooks are referring to a leakage flux due to secondary winding, because according to my concept that every flux line passing through the secondary must also pass through primary (from where it is originating)
     
  2. Glenn Holland

    Member

    Dec 26, 2014
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    The term "Leakage Flux" is actually a misnomer.

    If the primary and secondary windings are closely spaced on the core - and the core is not saturated, the flux through both windings will be the same. The actual cause of inefficiency in a transformer is mostly due to the resistance of the primary and the secondary windings. Eddy currents induced in the core itself are another cause of inefficiency.
     
  3. crutschow

    Expert

    Mar 14, 2008
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    Your transformer concept is not complete. ;)
    The secondary winding creates flux (in opposition to the primary flux) when there is any output current due to a load. It is this opposition flux that causes more primary current to maintain the core flux value constant (the transformer action).
    This secondary flux can have a leakage component, the same as the primary flux.
     
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  4. crutschow

    Expert

    Mar 14, 2008
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    Don't understand why you say that. :confused:
    Most of the primary winding flux does go through the secondary winding in a well made transformer, but not all. That causes a leakage component and all transformers have some.
    It can be the source of voltage spikes in switching transformers, for example.
     
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  5. Glenn Holland

    Member

    Dec 26, 2014
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    Looks like I stuck my head on the chopping block by trying to redefine terminology.

    When the current changes in the primary, it also induces a counter magneto-motive force (CMMF) in the core in accordance with Lenz's Law. This CMMF opposes the original flux (what would be expected to flow in a static DC condition). The "collision" of flux lines causes some of it to take a "detour" through the air gaps between each part of the core. The same phenomenon occurs in the secondary.

    http://www.vias.org/matsch_capmag/matsch_caps_magnetics_chap6_05_03.html

    It's like when two magnets are placed with the same polarity facing each other and the flux will be in repulsion and "spread out" instead of going through the magnets.

    In my humble opinion is it's more of a "reactive" phenomenon than simply "leakage", but what the Hell I should not be trying to rewrite the books.
     
  6. Ammar Aziz

    Thread Starter New Member

    Aug 23, 2015
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    Thank you for explaining so clearly. I am also thinking in the same manner, just looking for validation
     
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