# Autotransformer: Explain their Function in detail

## What is an Auto Transformer?

An Auto Transformer is a transformer in which there a single winding is provided on a laminated core.

An auto transformer is given like a two winding transformer but there is a difference between the two with reference to the position of primary and secondary winding.

Let a segment of the winding be common for both primary and secondary sides.

In load condition the load part of the current is taken directly from the supply and the other part is taken through transformer action. An Auto transformer is used for voltage regulating.

## Function of an Auto Transformer

In auto transformer apart from electric coupling, there is also magnetic coupling between the primary and the secondary winding.

However, one portion of the single unbroken coil is interconnected with the other part of the primary and secondary.

Depending on the construction the auto transformer is of two types.

• One type of transformer has the winding connected end to end with the turns connected to slots at convenient locations depending on the required secondary voltage.
• However, in another category of Auto transformer, there is more than one coil winding which is electrically in turn forming a continuous loop.

There is the primary winding AB from which a tapping at C is given for use thus making CB to be equivalent to a secondary winding.

The supply voltage to the operational amplifier is connected at AB while the load is connected at CB.

The tapping may be of fixed type or of variable type. When AC voltage V1 is applied across AB, an alternating flux is set up in the core

Now, because of the setup of the flux in the core, an emf E1 is induced in the winding AB. This induced emf is split between the various turns of the secondary coil with a part of it taken in the secondary circuit.

Overlooking no-load current, leakage reactance and losses,

Here

• Volumetric flow 1 is mentioned as V1=E1 and
• Volumetric flow 2 is referred as V2=E2.

Therefore, the transformation ratio:

K = V2 / V1 = N2 / N 1 = I1 / I 2

• Compared to the 2-winding transformer, An autotransformer has smaller the core and copper losses hence it has high efficiency.
• Autotransformer working basically calls for less conductor material compared to the 2-winding transformer.
• Lower voltage drops in resistance and leakage reactance lead to an increased voltage regulation.
• Smaller in size and cheaper than 2- Winding Transformer but contains more no: of windings.
• They demand a relatively low amount of excitation current, compared to the main field current.
• An autotransformer is capable to bringing into being variable voltages.