Autotransformer – Introduction, Advantages and Applications

Autotransformer – Introduction, Advantages and Applications.

In my previous post you read why the transformer is rated in KVA but not in KW, now in this post I am going to describe a type of transformer used in electrical and electronics domain. This post is about autotransformer. Well autotransformer is also called as ‘Variac’, because it is basically used to continuously vary the voltage supplied to the circuit.

Some of you may know about the general type transformers used in electrical power systems. In those kinds of transformers, there are 2 types of winding one is primary winding while the other is secondary winding. Both of these windings are physically separated or insulated from one another but are magnetically linked to each other.

In the case of autotransformers, the both the windings that is primary and secondary windings are connected to each other both physically and magnetically. There is one common winding which forms both primary and secondary winding in which voltage is varied by changing the position of secondary tapping on the body of the coil.


Now let us discuss some facts related to the advantages of autotransformers over the conventional transformers of the same rating.

Advantages of Autotransformers:

  1. Its efficiency is more when compared with the conventional one.
  2. Its size is relatively very smaller.
  3. Voltage regulation of autotransformer is much better.
  4. Lower cost
  5. Low requirements of excitation current.
  6. Less copper is used in its design and construction
  7. In conventional transformer the voltage step up or step down value is fixed while in autotransformer, we can vary the output voltage as per out requirements and can smoothly increase or decrease its value as per our requirement.

Talking about some of the modern day use of autotransformers:

  1. Used in both Synchronous motors and induction motors.
  2. Used in electrical apparatus testing labs since the voltage can be smoothly and continuously varied.
  3. They find application as boosters in AC feeders to increase the voltage levels.

If you have any doubts or queries related to this post, you can post your comments below. I would be glad to answer them. Do share this if you liked the post.

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