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Public-images-osm logo.svg windings:auto
Power autotransformer distribution1.jpg
Auto-transformer architecture for some power transformers Show/edit corresponding data item.
Group: power
Used on these elements
may be used on nodesshould not be used on waysshould not be used on areasshould not be used on relations (except multipolygon relations)


Useful combination
Status: approvedPage for proposal

An Auto-transformer (421-01-11) is a particular transformer architecture, with only one winding on which several voltage points are plugged towards usual interfaces. It could be used for mostly all roles.
You could find such auto-transformers in distribution, transmission, traction or converter substations.
This key lets mappers state if a given auto-transformer is main or auxiliary.

Auto design could be achieved with star, delta or others winding arrangements, then it wasn't possible to add windings:configuration=auto neither.
windings:auto=yes allows combinations with windings:configuration=star, windings:configuration=delta as to state the actual windings arrangements.

Auto-transformers use to get a lower rate between their voltage:primary=* and voltage:secondary=*.

See power=transformer for more information and examples.

Windings counting

Auto transformer.svg

Auto architecture changes a bit how windings are counted. windings=* is still expected on those transformers.

Usually, secondary interface is plugged on the same winding as the primary one like on the picture. Such transformers can still have tertiary, quaternary windings as well
Then, windings=* is expected to get a minus-1 value from a normal transformer.
A transformer with primary/secondary will get windings=1. A tertiary interface will change it to windings=2 and so on.


Photo Location Tagging Note
Power autotransformer distribution1.jpg France


A small plate indicates this transformer is an auto-transformer with a dedicated symbol. No tertiary interface here, so windings=1.