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What is an autotransformer? Here are the top things you need to know.

Autotransformers contain only one winding with a portion of the coil serving as both the primary and secondary winding. This unique design guides performance and the best use for applications. Let’s explore more to fully answer the question: What is an autotransformer?

How does an autotransformer work?

Autotransformers have a singular winding, in which the primary and secondary windings are connected both magnetically and electrically. In comparison, conventional transformers have two separate windings and are electrically insulated from each other.

Because of an autotransformer’s design, each opposing side of the coil acts as the primary or secondary side based on which part of the coil is linked to the load versus the power supply. This allows the autotransformer to provide the same function as a conventional transformer.

What is an autotransformer used for?

Autotransformers are often used in step-up or step-down applications. Common applications include boosting supply voltage in distribution systems to compensate voltage drops and starting induction and synchronous motors (autotransformers with taps). They can also be used as variac in conditions where continuous variable voltage over a broad range is needed, or as a voltage regulator for power systems of various voltage levels.

What are the advantages of autotransformers?

Depending on the application needed, there are benefits to using autotransformers compared to conventional transformers. Advantages can include:

  • Smaller size, lower cost and less conductor material required
  • Lower losses compared to an ordinary 2-winding transformer
  • Better voltage regulation
  • Smaller excitation current required
  • The ability to produce variable output voltage

It’s important to keep in mind the disadvantages as well, which can include:

  • Inability to isolate two circuits electrically because it’s not electrically isolated
  • Potential larger short circuit currents resulting from reduced internal impedance
  • Not suitable for interconnecting high and low voltage systems
  • Requirement for both sides to have their neutrality earth or isolated (not one side only)
  • Potential damage to connected equipment if there is an open circuit in the common portion (the full primary voltage is applied to the load on the secondary side)

What is an autotransformer that’s best suited for your industry?

SNC’s autotransformers, available in three-phase and single-phase models, are typically used in low-voltage situations of 600 volts or less. Need help determining if an autotransformer is right for your application? Contact our friendly experts to find out what’s best for you.