Transcript EQUIVALENT CIRCUIT OF TRANSFORMER

EQUIVALENT CIRCUIT OF
TRANSFORMER
Lecture No. 5
By: Sajid Hussain Qazi
Equivalent Circuit of Ideal Transformer
Equivalent Circuit of Practical Transformer
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For the non ideal or practical iron-core transformer,
the equivalent circuit appears as in figure below:
Equivalent Circuit of Practical Transformer
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As indicated, part of this equivalent circuit includes an
ideal transformer.
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The remaining elements of Figure are those elements
that contribute to the non ideal characteristics of the
device.
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The resistances Rp and Rs are simply the dc resistance of
the primary and secondary windings, respectively.
Equivalent Circuit of Practical Transformer

For the primary and secondary coils of a
transformer, there is a small amount of flux that links
each coil but does not pass through the core, as
shown in Figure below for the primary winding.
Equivalent Circuit of Practical Transformer

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This leakage flux, representing a definite loss in the
system, is represented by an inductance Lp in the
primary circuit and an inductance Ls in the secondary.
The resistance Rc represents the hysteresis and eddy
current losses (core losses) within the core due to an
ac flux through the core.
The inductance Lm (magnetizing inductance) is the
inductance associated with the magnetization of the
core, that is, the establishing of the flux Φm in the
core.
Equivalent Circuit of Practical Transformer
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The capacitances Cp and Cs are the lumped
capacitances of the primary and secondary circuits,
respectively, and Cw represents the equivalent
lumped capacitances between the windings of the
transformer.
The capacitances Cp, Cw, and Cs do not appear in
the equivalent circuit, since their reactance at typical
operating frequencies will not appreciably affect
the transfer characteristics of the transformer.
Equivalent Circuit of Practical Transformer

Since i′p is normally considerably larger than iΦm (the
magnetizing current), we will ignore iΦm for the
moment (set it equal to zero), resulting in the
absence of Rc and Lm in the reduced equivalent
circuit of Figure.
Reduced equivalent circuit of transformer