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Autotransformers and Variacs

The autotransformer is a static piece of electrical equipment that uses electromagnetic induction to transfer power from one voltage system to another. The transformer helps to match the voltage of the load to the line voltage that the utility supplies. Transformers and variacs, their subtype, can come in various forms and include several kinds of features, so do learn a bit more about this kind of equipment before purchasing it or power transformer parts or accessories.

Autotransformer Basics

The autotransformer is a certain type of transformer. It stands out for having only one winding wound on the laminated core. It does resemble a two winding transformer, but its primary and secondary winding are interrelated in a different way, as part of the winding is common for them both. Basically, an autotransformer is like a voltage regulator in terms of its function.

Autotransformer Applications

The autotransformer functions as a starter that gives about half of the required full voltage to the motor that it helps to starts. It can also provide a small boost for a distribution cable when correcting the voltage drop. Moreover, it acts as a voltage regulator. You commonly use the autotransformer in railways, audio systems or power transmission and distribution systems. You can commonly find the transformer's suitable applications from its specifications list. For instance, you could purchase dedicated LAN Ethernet transformers for your networking needs.

Advantages of Autotransformers

Compared to the similar two winding transformer, the autotransformer is generally less expensive and regulates the voltage more efficiently. In addition, compared to a two winding transformer that has the same rating, the autotransformer experiences less losses.


Variacs are a subtype of autotransformers. In fact, their name refers to their function, as "variac" means a variable transformer. They are the most popular type on the market because they are much lighter and smaller than dual-winding transformers. These AC power supplies can be either energy-saving or heavy-duty industrial models that can handle even the most difficult tasks.

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