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Lossess In a Transformer

  1. Sep 11, 2005 #1
    Hi Guys!!

    Well! im studying transformer and i want to know about the following losses in a transformer:

    1)Hysteresis Losses
    2)Eddy Current Losses
    3)Copper Losses
    4)Stray Losses

    please explain me the right concept. I have studied so much but im just not getting the right concepts to understand these losses.

    Thanks in advance
     
  2. jcsd
  3. Sep 12, 2005 #2
    There are mainly two kinds of losses in a transformer,namely
    (1)core loss.
    (2)Ohmic loss.
    1.Core loss:

    These core losses in transformer consists of two components hysteresis loss and eddy current loss
    i.e. core loss=hysteresis loss+eddy current loss.
    hysteresis losses depends on applied voltage and its frequency
    eddy current loss is proportional to squre of the applied votage and is independent of frequency f.
    3.Ohmic loss:
    when transformer is loadded ohmic losses(i^2*r)occurs in both the primary and secondary winding resisrances.
    In addition to core loss the follwing loss has to be taken into consideration

    Stray losses: Leakage fields present in the transformer induce eddy currents in conductors,tanks,channels,bolts etc. and these eddy currents give rise to stray losses.
     
    Last edited: Sep 12, 2005
  4. Oct 20, 2005 #3
    CORE LOSSES:


    I. the energy dissipated in the core due to hysterisis over one cycle is the area enclosed by the hysterisis loop:
    [tex]E_{\mbox{per cycle}}=\oint B(H)dH[/tex],

    where [tex]B[/tex] and [tex]H[/tex] are the magnetic field (flux density) and magnetizing intensity (or auxilliary field or just "H") present in the core. Physically, this loss is understood as the energy required to orient and reorient the magnetic domains in the ferromagnetic material, when the direction of the magnetic field changes due to the A.C. current. The rate of dissipation is basically the area enclosed by the curve times the frequency.

    II. Eddy current is a consequence of faraday's law of voltage induction: when A.C. current is applied to the windings, this changing current results in a magnetic flux which "flows" through the core of the transformer-- this flux is proportional to the current, so it is also CHANGING in time. Time changing fluxes induce time changing electromotive forces. The induced emf's are loops which are essentially around the path of the flux in a cylindrical manner; since the core material (iron) is a conductor, the induced emf's will give rise to currents that swirl around the loop of the emf.

    OHMIC LOSS:
    This one is the easiest to understand-- The copper windings of the primary and secondary of the transformer are (obviously) conductors, so some energy will be dissipated in them. The copper wire of the primary and secondary will have total resistances of [tex]R_{P}[/tex] and [tex]R_{S}[/tex]; energy will dissipate in them at a rate of [tex]
    P_{\mbox{ohmic}}=I_{P}^2R_{P}+I_{S}^2R_{S}[/tex].
    Note that the resistances of the wires depend on frequency to some extent-- higher frequency, higher resistance (skin effect).

    STRAY LOSSES:
    Since the world is not "ideal" air has some finite albeit small magnetic permeability [tex]\mu_{\mbox{air}}\approx\mu_{0}=4\pi \times 10^-^7\mbox{H/m}[/tex], which means it presents a LARGE reluctance to magnetic flux, so some of the flux will "leak" out of the core of the transformer. As a model, you can view the air and core as two reluctances (the magnetic analog of resistnace) in "parallel". The smaller reluctance - the path formed by the iron core - will take most of the flux, since the larger reluctance - the air - is not infinite in value some flux loops out and passes through it. If there are conducting materials in the path you can again have losses from the farady induction in those materials.


    Hope this helps. If you aren't familiar with the concept of reluctance, I suggest searching magnetic circuits concepts, also search for the full equivalent circuit model of the transformer. All of these losses, can be modelled to an approximation with inductances and resistances.
     
    Last edited: Oct 20, 2005
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