# What is Auto Transformer?

An autotransformer is a type of Electrical transformer which consists of a Single winding called autotransformer. This single winding is commonly used as primary and secondary. The principle of this transformer is the same as another transformer.

## Why do we need an Autotransformer?

sometimes we need a small change in the voltages for example 110 volts to 129 volts or 13.2kv to 13.8kv. if we use two winding transformers the cost of the transformer is increased x times. so to overcome this problem we used a single-winding transformer that is called autotransformer. The relation of first winding to second winding we refer to as the turn ratio. The first winding is called common winding and the second winding is called series winding of the transformer. The input voltage is equal to the sum of the series winding and common winding voltage. The output voltage is equal to the common winding voltage.

### Transformation Ratio

V2/V1 =N2/N1 = K
The K is called the transformation ratio.

## Applications Of Auto Transformer

1. Autotransformer is used as a booster in the feeder.
2. To start the induction and synchronous motor.
3. Autotransformer used as arc Furnace Transformer.
4. Autotransformer is used as a balance set in different ratings of the transformer.
5. To provide a neutral three-wire lighting system
6. To provide step-down voltage in single-phase railway electrification.
7. To provide different voltages for testing purposes in electrical equipment.
8. To provide neutral in three wire direct current generator.
9. Autotransformers are used in long transmission lines.
10. Autotransformer is used as a variable voltage.
11. the autotransformer is used to step down the voltage.