Editing Transformer (section)

===Ideal transformer===
An ideal transformer is [[Linearity|linear]], lossless and perfectly [[inductive coupling|coupled]]. Perfect coupling implies infinitely high core [[Permeability (electromagnetism)|magnetic permeability]] and winding [[inductance]] and zero net [[magnetomotive force]] (i.e. ''i''<sub>''p''</sub>''n''<sub>''p''</sub>&nbsp;−&nbsp;''i''<sub>''s''</sub>''n''<sub>''s''</sub>&nbsp;=&nbsp;0).<ref name="Brenner18-6">{{harvnb|Brenner|Javid|1959|loc=§18-6 The Ideal Transformer, pp. 598–600}}</ref>{{efn|This also implies the following: The net core flux is zero, the input impedance is infinite when secondary is open and zero when secondary is shorted; there is zero phase-shift through an ideal transformer; input and output power and reactive volt-ampere are each conserved; these three statements apply for any frequency above zero and periodic waveforms are conserved.<ref name="Crosby1958-145">{{harvnb|Crosby|1958|p=145}}</ref>}}

[[File:Transformer under load (alternative version).svg|left|thumb|upright=2|Ideal transformer connected with source ''V''<sub>''P''</sub> on primary and load impedance ''Z''<sub>''L''</sub> on secondary, where 0&nbsp;<&nbsp;''Z''<sub>''L''</sub>&nbsp;<&nbsp;∞.]]
[[File:Transformer3d col3.svg|left|thumb|upright=2|Ideal transformer and induction law{{efn|Direction of transformer currents is according to [[Right-hand rule#Rotations|the Right-Hand Rule.]]}}]]

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A varying current in the transformer's primary winding creates a varying magnetic flux in the transformer core, which is also encircled by the secondary winding. This varying flux at the secondary winding induces a varying [[electromotive force| electromotive force or voltage]] in the secondary winding. This electromagnetic induction phenomenon is the basis of transformer action and, in accordance with [[Lenz's law]], the secondary current so produced creates a flux equal and opposite to that produced by the primary winding.

The windings are wound around a core of infinitely high magnetic permeability so that all of the magnetic flux passes through both the primary and secondary windings. With a [[voltage source]] connected to the primary winding and a load connected to the secondary winding, the transformer currents flow in the indicated directions and the core magnetomotive force cancels to zero.

According to [[Faraday's law of induction|Faraday's law]], since the same magnetic flux passes through both the primary and secondary windings in an ideal transformer, a voltage is induced in each winding proportional to its number of turns. The transformer winding voltage ratio is equal to the winding turns ratio.<ref>Paul A. Tipler, ''Physics'', Worth Publishers, Inc., 1976 {{ISBN|0-87901-041-X}}, pp. 937–940</ref>

An ideal transformer is a reasonable approximation for a typical commercial transformer, with voltage ratio and winding turns ratio both being inversely proportional to the corresponding current ratio.

The load impedance ''referred'' to the primary circuit is equal to the turns ratio squared times the secondary circuit load impedance.<ref name="Flanagan1993-1">{{cite book| last = Flanagan| first = William M.| title = Handbook of Transformer Design & Applications| publisher = McGraw-Hill| year = 1993| edition = 2nd| isbn = 978-0-07-021291-6|url=https://archive.org/details/FlagananHandbookOfTransformerDesignApplications}} pp. 2-1, 2-2</ref>
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