Autotransformatorer

Autotransformatorer, commonly called autotransformers, are a type of transformer characterized by a single winding that serves as both the primary and secondary, with only part of the winding common to both circuits. A tap along the winding provides the secondary voltage. The input is applied between one end and a tap; the output is taken between the other end and a different tap, so the voltage ratio equals the turns ratio of the respective sections. Because the primary and secondary share windings, there is no galvanic isolation, which implies potential shock hazard and limits certain safety applications. The design is more material-efficient than two-winding transformers for large voltage differences or high voltages, because less copper and core material are required. Consequently, autotransformers can handle similar power levels at lower cost, but their lack of galvanic isolation means the kVA rating is not directly comparable to that of a two-winding transformer.

They are widely used for voltage regulation and conversion, such as starting autotransformers for induction motors, continuous voltage regulators, and portable variable transformers (variacs). In distribution systems, autotransformers are used to step voltages up or down with relatively small phase shift, for example in voltage boosters or glide-type regulators, where isolation is not required. Safety considerations include not drawing power from the common winding regardless of configuration, ensuring proper grounding, and avoiding connection to circuits requiring isolation. Typical construction uses a laminated core and a single continuous winding with several taps, or two coils connected in series with a common junction. Regulation and efficiency depend on load and tap position. In summary, autotransformers offer compact, economical voltage conversion where isolation is not essential.