Editing Transformer (section)

===Windings===
[[Image:Transformer-hightolow smaller.jpg|thumb|Windings are usually arranged concentrically to minimize flux leakage.]]
[[Image:transformer min stray field geometry.svg|thumb|left|Cut view through transformer windings.
Legend: <br />
'''White''': Air, liquid or other insulating medium <br />
'''Green spiral''': [[Electrical steel|Grain oriented silicon steel]]<br />
'''Black''': Primary winding <br />
'''Red''': Secondary winding
]]
The electrical conductor used for the windings depends upon the application, but in all cases the individual turns must be electrically insulated from each other to ensure that the current travels throughout every turn. For small transformers, in which currents are low and the potential difference between adjacent turns is small, the coils are often wound from [[enameled wire|enameled magnet wire]]. Larger power transformers may be wound with copper rectangular strip conductors insulated by oil-impregnated paper and blocks of [[Transformerboard|pressboard]].<ref name="CEGB1982">{{harvnb|CEGB|1982|}}</ref>

High-frequency transformers operating in the tens to hundreds of kilohertz often have windings made of braided [[Litz wire]] to minimize the [[Skin effect|skin-effect]] and proximity effect losses.<ref name="dixon">{{Cite conference | first = Lloyd| last = Dixon| book-title = Magnetics Design Handbook| title = Power Transformer Design|url=http://focus.ti.com/lit/ml/slup126/slup126.pdf| year=2001| publisher = Texas Instruments}}</ref> Large power transformers use multiple-stranded conductors as well, since even at low power frequencies non-uniform distribution of current would otherwise exist in high-current windings.<ref name="CEGB1982"/> Each strand is individually insulated, and the strands are arranged so that at certain points in the winding, or throughout the whole winding, each portion occupies different relative positions in the complete conductor. The transposition equalizes the current flowing in each strand of the conductor, and reduces eddy current losses in the winding itself. The stranded conductor is also more flexible than a solid conductor of similar size, aiding manufacture.<ref name="CEGB1982"/>

The windings of signal transformers minimize leakage inductance and stray capacitance to improve high-frequency response. Coils are split into sections, and those sections interleaved between the sections of the other winding.

Power-frequency transformers may have ''taps'' at intermediate points on the winding, usually on the higher voltage winding side, for voltage adjustment. Taps may be manually reconnected, or a manual or automatic switch may be provided for changing taps. Automatic on-load [[tap changer]]s are used in electric power transmission or distribution, on equipment such as [[arc furnace]] transformers, or for automatic voltage regulators for sensitive loads. Audio-frequency transformers, used for the distribution of audio to public address loudspeakers, have taps to allow adjustment of impedance to each speaker. A [[Center tap|center-tapped transformer]] is often used in the output stage of an audio power [[amplifier]] in a [[Push-pull converter|push-pull circuit]]. Modulation transformers in [[Amplitude modulation|AM]] transmitters are very similar.