What is an autotransformer?

An autotransformer is a special case, in which one coil becomes part of another coil. Autotransformers are also often used for starting motors. An autotransformer is an electrical transformer with only one winding, and portions of the same winding act as both the primary winding and secondary winding sides of the transformer.

For an autotransformer, portion of the winding is shared by both the high-voltage side and the low-voltage side. The other part only belongs to the high-voltage side. According to the structure, it can also be subdivided into two types: adjustable pressure type and fixed type. Auto-coupling means electromagnetic coupling. Ordinary transformers transfer energy through the electromagnetic coupling of the primary and secondary coils, in which there is no direct electrical connection between the primary and secondary sides. However, the primary and secondary sides of the autotransformer have direct electrical connections, and the low-voltage coils are part of the high voltage coils. An autotransformer works on the same principle as that of an ordinary transformer, except that its primary coil is its secondary coil. In a general transformer, the primary side coil generates voltage on the secondary side through electromagnetic induction. The autotransformer affects itself.

An autotransformer is an electrical transformer with only one winding. Compared with ordinary transformers of the same capacity, autotransformers are not only smaller in size, but also more efficient. In addition, the larger the capacity of the transformer is, the higher the voltage is, and this advantage becomes more outstanding. Therefore, with the development of power systems, an increase of the voltage level and the increasing transmission capacity, autotransformers have been widely used because of their high capacity, low loss, and low cost.