Different Types of Transformer

A transformer is an important electrical device used in transmission and distribution systems. It step-up or step-down voltage or current. There are different types of transformer used for different applications. In this article, we will see transformer types and their important features.

Different Types of transformer

The transformer can be classified as

(1). Based on voltage levels

  • Step-up transformer
  • Step-down transformer
  • Isolation transformer

(2). Based upon application

(i) Electrical domain

  • Distribution transformer
  • Power transformer
  • Instrument transformer

Instrument transformer can be classified as

  1. Current transformer
  2. Potential transformer or Voltage transformer

(ii) Electronics domain

  • Pulse transformer
  • Audio Output Transformer

(3). Based on the number of phases

  • Single-phase transformer
  • Three-phase transformer

(4). Based on the winding arrangement

  • Two-winding transformer
  • Auto transformer

(5). Based on Core material

  • Air core transformer
  • Iron core transformer
  • Ferrite core transformer
  • Toroidal core transformer

Transformer types based on voltage levels

1. Step-up transformer

When the number of secondary winding turns is more than the primary winding turns, such a transformer is known as a step-up transformer. This transformer step-up voltage and step-down current.

This transformer is used where we need higher voltage and lower current as compared to input.

2. Step-down transformer

When the number of secondary winding turns is less than the primary winding turns, such a transformer is known as a step-down transformer. This transformer step-down voltage and step-up current.

This transformer is used where we need lower voltage and higher current as compared to input.

3. Isolation transformer

When the number of primary winding turns is equal to the secondary winding turns, such a transformer is known as an isolation transformer. This transformer is used for isolating the source and load sides.

The voltages on the source and load sides are equal. This transformer is used for isolation purposes.

Transformer types based on the number of phases

1. Distribution transformer

These are the transformer which is used for stepping down the voltage from transmission side to distribution side (house or industry).

These transformers are in operation 24 hours a day no matter they carry any load or not. The distribution transformer is designed with small leakage reactance and good voltage regulation.

Learn more about distribution transformers.

2. Power transformer

These are the transformer which is used at the end of transmission line in generating stations or substations. They can step up voltages in generating stations and step down voltages in substations.

These transformers are in operation during load periods only. They are disconnected during the light load periods. The power transformer is designed with higher leakage reactance compared to the distribution transformer. The power transformers are also designed to have maximum efficiency at or near full load.

Learn more about power transformers.

Difference between Power transformer and Distribution transformer

3. Instrument transformer

These are the transformer which is used indirectly in measuring high voltages and high current in high voltage circuits. It is not safe to measure voltage or current in the range of kilo or mega with the help of measuring instruments. Also, such ratings of instruments are impractical.

To solve such problems, the instrument transformers step down high voltage or high current to a safe value. This safe value can be easily measured with a voltmeter or an ammeter. The instrument transformer is of two types i.e.

  1. Current transformer
  2. Potential transformer
(i) Current transformer

It is an instrument transformer that steps down the current from a higher current to a lower current (safe value). This lower current can be easily measured by an ammeter. The measured value is proportional to the high current (in the HV circuit) to be metered.

(ii) Potential transformer

It is also known as voltage transformer. It is an instrument transformer that steps down the voltage from a higher voltage to a lower voltage (safe value). This lower voltage can be easily measured by a voltmeter. The measured value is proportional to the high voltage (in the HV circuit) to be metered.

Transformer types based on the number of phases

1. Single-phase transformer

A transformer that accepts a single-phase AC supply and provides a single-phase AC output, is known as single-phase transformer.

2. Three-phase transformer

A transformer that accepts a three-phase AC supply and provides a three-phase AC output, is known as three-phase transformer. This transformer is used in three-phase systems.

Transformer types based on the winding arrangement

1. Two-winding transformer

This transformer has two windings i.e. primary and secondary. Both windings are electrically isolated i.e. there is no electrical connection between the primary winding and the secondary winding.

2. Auto transformer

It is a special type of transformer having only one winding. A part of the winding is common to both low voltage and high voltage sides. There is an electrical connection between low voltage and high voltage sides.

Transformer types based on core material

1. Air core transformer

This does not use any core material for flux to set up. This is basically two coils separated by air. There is flux linkage in the coils using the air. The flux linkages in the coils are very few. Hence the efficiency of the air core transformer is poor.

2. Iron core transformer

This transformer uses thin plates of soft iron as core material for flux to set up. The flux linkages in the coils are very high. Hence the efficiency of the iron core transformer is very high.

3. Ferrite core transformer

This transformer uses ferrite as core material for flux to set up. The magnetic permeability is very high. The losses in the transformer are very less under high-frequency applications. Hence ferrite core transformer is best for high-frequency applications.

4. Toroidal core transformer

The shape of the core of this transformer is a toroid or ring. It can be made of soft iron or ferrite material. It has very low leakage inductance.

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