It is common to hear an autotransformer called an auto-step down or auto-step up transformer, as this is the basic task of the component. As with all types of transformers, the autotransformer uses windings to result in the part functioning as a voltage regulator in the device or system.
A 3 phase autotransformer uses the same principles. It has one winding, hence the term “auto,” and the winding acts as both the primary and secondary side. In a three phase transformer, the three single phases transformers are connected by the winding, which provides significant benefits for many applications.
The Basic Design
The single winding connecting the three phases can be tapped at specific points along the winding. This allows a specific drop in the primary voltage to be accessed as the energy flows through the winding. These taps can be placed in different locations as required by the specific equipment, machine or system.
The 3 phase autotransformer also has two end terminals, just like all other transformers, including the single phase designs. The primary voltage will come into the system on two of the terminals, and it will also be accessed through the use of two terminals. In most cases, one of the terminals used for the secondary voltage will also be common to the primary voltage.
With this type of design, including the use of compact cores, the design of the 3 phase autotransformer can be much smaller than would be possible by connecting three single phase transformers.
There are different configurations for 3 phase autotransformers. These include the Wye configuration, which is sometimes called the star configuration, as well as the Delta or mesh configuration. Choosing the correct configuration for the specific application will be essential as well locating the taps and choosing the core in the transformer.