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    An autotransformer, also known as a step-down transformer, is an electrical transformer with only one winding. The winding has at least 3 taps where electrical connections are made. Autotransformers have the benefit of being small, light and cheap compared to dual-winding transformers.

    Autotransformers are used to step up or step down voltages in the 110V-115V-120V range and 220V-230V-240V range. This allows electrical equipment from the US to be fed from higher European voltage.


    • Can be used as a method of soft starting induction motors

    • In UK railway applications

    • In audio applications, tapped autotransformers are used to adapt speakers to constant-voltage distribution systems

    • Power applications to interconnect systems operating at different voltages

    • Special autotransformers are used on rural power distribution lines so that customers further away receive the same average voltage as ones nearer to the source

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