Three Phase Autotransformer

At Johnson ElectricCoil Company, we work with many different OEMs to create custom transformers, inductors, and other custom magnetics. Many of our customers have worked with us for decades, trusting us to provide them with personalized support, information, and assistance to ensure their orders are right every time.

Not all OEMs are necessarily familiar with custom magnetics, though. It can be difficult to discern the various terms and the differences between different options in transformers, so taking a closer look at the components of each type can be very helpful.

One type of transformer that is used in a wide variety of applications is the 3 phase autotransformer. When saving physical space, boosting efficiency, and managing voltage are critical for the application, a 3 phase autotransformer may be a practical, cost-effective option to consider.

The Autotransformer


Like most transformers, an autotransformer is used to step down or step up power through a system. The defining feature of an autotransformer is that it has only a single winding, and a section of that same winding is shared by both the input (primary) and output (secondary) side of the circuit. Consequently, unlike the more familiar isolation transformer, there is no physical or electrical separation—isolation, that is—between the input and output windings of an autotransformer. Instead, a single winding that accommodates the highest specified voltage is tapped at a given point in order to access the required step-up or step-down voltage.

The Advantages

While neither single phase nor 3 phase autotransformers provide electrical isolation between input and output, where isolation is not required, an autotransformer is often an attractive choice for step-up and/or step-down requirements. One advantage is that a 3 phase autotransformer is typically and sometimes significantly smaller in size than a similarly rated three phase isolation transformer. For many custom applications, where minimizing weight and footprint can be critical, this may be an essential consideration. And thanks to its comparatively small size, a 3 phase autotransformer affords a cost savings as well. Finally, in terms of performance, a 3 phase autotransformer is highly efficient.

Essentially a very simple component, when designed by our team to your specifications, the 3 phase autotransformer will provide the step-up or step-down power you need, all in a minimum of space, with maximum efficiency, and within your budget.