basics of autotransformer

bhargava wrote:


Looking at the schematic symbol for the device explains all:
http://commons.wikimedia.org/wiki/Image:Autoxfmr.png

A good resource you should know: http://en.wikipedia.org http://en.wikipedia.org/wiki/Autotransformer
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I can explain single phase operation: Typically refereed to as buck/boost in the field, I tend to reserve the term autotransformer for the three phase versions of the same concept. The feed for the primary windings of the transformer continue on to the load after being manipulated by the secondary windings. With a standard 10:1 ratio transformer that would be used for control power, i.e.: 240 volts down to 24, or 120 volts down to 12, you could boost 208 volts up to a more tolerable range for machine sensitive to a 230 volt feed. The voltage would be subtractive if passed through the secondary windings in reverse.
The application is limited though, generally to about a 20% manipulation of the original voltage.
The advantage is reduced size, (since the windings so not carry the entire load), & cost if you are not purchasing a special order item.. ______________________ ____________/ ___________________ 208 + 20.8 = 229 volts 208 volts____________P ][ S \__/ 10:! ratio general purpose transformer
You can obtain good information at the Acme transformer website. evo
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Just to point out a fact that I have designed several 1:1 ratio autotransformers in the past. So yes they are out there.
Their principle use is as a phase shift transformer, generally at mains voltage they help to give 12 pulse rectification if one bridge is connected direct to the mains.
Euclid

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