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Types of Transformer

Last updated: Sep 26, 2020

There are various types of transformer, each with its own applicable usage. However, the main objective of using them is the same – transforming electrical power from one type to another. 

In this blog, we will aim at enlightening the readers about Transformer basics and working principle, types of transformer on the basis of voltage, medium, uses, configuration and place of usage, their advantages and limitations.



A Transformer is an electrical device that can be used to transfer the power from one circuit to another by using the principles of electromagnetic induction. There are two types of winding in the transformer i.e. Primary winding and the secondary winding. Primary winding means a winding to which an AC supply is connected and the secondary winding means a winding to which a load is connected. The voltage will be raised or lowered in a circuit, but with a proportional increase or decrease in the current ratings.

Hello there! On a related topic, we previously wrote a blog about Transformers — Its Working, Construction, Types, and Uses. If this peaks your interest, check it out and let us know what you think.

Working Principle of Transformer

The transformer working depends upon Faraday's law of electromagnetic induction. According to Faraday's laws,

"The Rate of change of flux linkage with respect to time is directly proportional to the EMF induced in a conductor or coil".

Faraday's Law

E= N dĪ• /dt


E = Induced EMF

N = the number of turns

dĪ• = Change in flux

dt = Change in time


One of AllumiaX's recent initiatives is a corporate sponsorship for the GeneralPAC platform which provides tutorials for power systems protection, automation and controls. Here, you will find the video series of Transformer. In this series they will be going over the Introduction to the Delta Wye Transformer ConnectionIntroduction to Wye Wye Transformer ConnectionIntroduction to Delta Wye Transformer Connection and Circulating Current and VoltagesOpen Phase Condition in Transformer AnalysisDifference Between Core Form and Shell Form Power Transformer



Types of Transformer

Transformer can be categorized on the basis of voltage level, medium, uses, configuration and place of usage. Now we will discuss each type in detail.

1. Based on Voltage Level

On the basis of voltage level, transformer types are listed below.

  • Step-Up Transformer
  • Step-Down Transformer
  • Isolation Transformer
Based On Voltage Level  Voltage  No. of Turns Current Rating of Output Voltage Uses
Step-Up Transformer Vs > Vp Np < Ns Ip > Is 220V - 11kv or above

Power Distribution

Doorbell, voltage converter, etc.

Step-Down Transformer Vs < Vp Np >  Ns Ip < Is

40-220v, 220-110v, or

110-24v, 20v 10v etc.

Power Transmission

(Power plants. X-rays machines, micro-waves, etc.)

Isolation Transformer Vs = Vp Np = Ns Ip = Is Output voltage which is identical to their input - known as 1:1 transformers Safety purpose insulation barrier, to cancel noise 

Step-Up Transformer

A Step Up Transformer is a device which converts low voltage at primary side to high voltage at secondary side. The primary winding of a coil has less number of turns than the secondary winding.


Vp/Vs = Ns/Np


  • Transmit electricity over long distances at low cost.
  • Helps in reducing the resistance on the line.
  • Ability to work continuously.
  • start operations immediately after its installation without any delays.
  • Highly efficient and suffer from very little losses.
  • Do not involve much time and money for maintenance.


  • Applications limited to AC operations only.
  • Use a round-the-clock cooling system i.e. makes the system bulky.

Step-Down Transformer

A Step Down Transformer is a device which converts high voltage at primary side to low voltage at secondary side. The secondary winding of a coil has less number of turns than the primary winding.


Vs/Vp = Ns/Np


  • Easy power transmission at low cost.
  • Highly reliable and efficient.
  • Provides varied voltage requirements.


  • Requires a lot of maintenance, which can damage the transformer.
  • Volatility in feedstock costs.
  • Fault rectification takes more time.

Isolation Transformer

Isolation transformer can be step-up transformer or step-down transformer but the primary and secondary voltage values are always equal i.e. turns ratio is always 1. This is obtained with a same number of turns on the primary and secondary windings. Isolation transformers are referred to as "insulated".


Vs/Vp = Ns/Np    Where Ns=Np


  • Provide safety to electronic components and the persons against electrical shock.
  • Suppress the electrical noise.
  • Avoids ground loops.
  • Provide available supply even if the device is broken.
  • Used as instrument transformers
  • Handle any amount of voltage necessary.


  • Produce distortion at secondary side when operates as pulse transformer.
  • When operating DC pulse signal, saturation of the core decreases.
  • High cost.

2. Based on the Core Medium

On the basis of core medium, transformer types are listed below.

  • Air Core Transformer
  • Iron Core Transformer
  • Ferrite Core Transformer
Based on Core Medium Core Material Flux Linkage Eddy Current Losses Reluctance Mutual Inductance Efficiency  Uses
Air-Core Transformer Non-magnetic strip Through the air  Low High Less Low Radio-frequency application
Iron Core Transformer Multiple soft iron plates Through the iron plate bunch Large Less High High Power distribution
Ferrite Core Transformer Ferrite core Through a window or hole Very Low Very Low Very High Very High Switch-mode power sup

Air Core Transformer

Air-core transformers are designed to transfer radio-frequency currents—i.e., used in radio transmitter and communication devices etc. As the name suggests, these transformers have no solid core, which makes them very light in weight, thus making them ideal for small-sized portable electronic devices. Air core transformers create flux using the windings and the air passing through them. This help air core transformer to completely eliminate undesirable characteristics of ferromagnetic core (eddy current losses, hysteresis, saturation, etc.)


  • Zero distortion.
  • Zero dissipation of signal quality.
  • Noise-free operation.
  • Lack of losses in hysteresis and eddy currents.
  • Lighter in weight.


  • Low degree of coupling (mutual inductance)
  • Unsuitable for use in power distribution.

Iron Core Transformer

In this type of transformer, primary and secondary windings are wounded on multiple iron plates. These iron plates provide perfect linkage path to the generated flux and serve analogous functions in the audio-frequency range. Iron core transformer are widely used and highly efficient as compare to air core transformer.


  • Handle large loads at a low frequency.
  • Offers less reluctance.
  • Highly efficient.


  • Large eddy current losses

Ferrite Core Transformer

Ferrite core transformer means a transformer whose magnetic core is made up of ferrite. Ferrites are non-conductive, ceramic compounds that are ferromagnetic in nature. The high magnetic permeability of these transformers makes them ideal for a variety of high frequency transformers, adjustable inductors, wide band transformers, common Mode Chokes, switched-mode power supply and radio frequency applications.


  • Low reluctance magnetic path.
  • High current resistivity.
  • Provides low eddy current losses over many frequencies.
  • High magnetic permeability, coercivity and Q-values.
  • Low hysteresis factor, DC sensitivity and signal distortion.


  • Easily saturated (its saturation flux density is typically < 0.5 T).
  • Permeability drifts with temperature.

3. Based on Usage

On the basis of usage, transformer types are listed below.

  • Power Transformers
  • Distribution Transformers
Based On Usage Types of Network Operating Condition Load Fluctuations Winding Conditions Insulated Level Designed Efficiency Application
Power Transformers Transmission network of higher voltages Always operated at full load Very Less  Primary winding connected with stars, secondary in delta High Maximum efficiency at 100% load Used in generating stations, and transmission substations
Distribution Transformers Distribution network of lower voltage Operated at load less than full load as load cycle fluctuates Very High Primary winding connected with delta, secondary in stars Low Maximum efficiency at 60% to 70% load Used in distribution stations also for industrial and domestic purposes

Power Transformers

Main principle of power transformer is to convert the Low voltage input to a high voltage output. This transformer acts as a bridge between the power generator and the primary distribution grid. This has complex construction due to high power generation and mainly installed at the generating stations and transmission substations. The power transformers are employed in the transmission networks of higher voltages.


  • Suitable for high voltage applications (greater than 33KV).
  • High insulation level.
  • Minimize the power loss.
  • Cost effective.


  • Loaded for 24 hours at transmission station, thus, the core and copper loss will occur for the whole day.
  • Big in size.

Distribution Transformers

Distribution transformers are step down transformer and used in distribution network for industrial and domestic purpose. These transformers convert High grid voltage to the end customer required voltage where the electrical energy is distributed and utilized at the consumer end. In order to distribute the power from power plant to remote locations, these transformers are used.


  • Small size.
  • Easy installation.
  • Low magnetic losses.
  • It is not always fully loaded.


  • Designed for 50-70% efficiency.
  • Low flux density as compare to power transformer.
  • Regular load fluctuations.
  • Time-dependent.

4. Based on Electrical Supply

On the basis of configuration, transformer types are listed below.

  • Single phase transformer
  • Three phase transformer
Based On Electrical Supply Power Supply Network No of Coils No of Terminals Voltage Power Transfer Capability Efficiency Uses
Single-Phase Transformer The power supply through one conductor Simple 2 4 Carry 230v Minimum Less For home appliances
Three-Phase Transformer The power supply through three-conductor Complicated 6 12 Carry 413v Maximum High

In large industries and for running heavy loads

Power or distribution transformer 


Single Phase Transformer

When there is only one coil at primary side and one coil at secondary side, then the transformer is called single phase transformer. Here the power supplies through a single conductor. This type of transformer accepts single-phase alternating current and output single-phase alternating current, typically at variant voltage level that operates in a unified time phase. These types of transformer are mostly used in the household devices.


  • Simple network.
  • Cost effective.
  • Most efficient AC power supply for up to 1000 watts.


  • Supply only 1-ph load.
  • used to light loads and small electric motors.
  • Minimum power transfer capability.
  • Power failure occurs.

Three Phase Transformer

Three phase transformer means the power flows through three conductors. Three phase transformer contains six coils, three coils at primary side and three coils at secondary side. This type of transformer accepts three-phase alternating current and output three-phase alternating current, typically at variant voltage level that operates in a unified time phase. These types of transformer are mostly used as a power or distribution transformers  


  • Large motors or heavy loads materials.
  • Transmission of power to long distance through magnetic field.
  • Maximum power transfer capability.
  • Power failures do not occur. 


  • Required many cooling systems depending on the transformer rated power.
  • Complex network.

5. Based on Place of Usage

On the basis of place of usage, transformer types are listed below.

  • Indoor Transformers
  • Outdoor Transformers
Based On Place Of Usage Cooling Medium Maintenance Cost Sound Operating Level Price Efficiency Uses
Dry-Type Transformers(Indoor) Air as the cooling medium Low Noise pollution exist Expensive Less efficient Public places like transportation hubs and company buildings
Oil-filled Transformers(Outdoor) Oil as the cooling medium High No noise pollution Cheap More efficient For outdoor, high rated application

Indoor Transformers

Indoor transformers are usually a Dry type transformer. These transformers use air as cooling medium and usually their primary and secondary side connections are isolated. Dry type transformers are installed in buildings and close to buildings because they are environmentally safer i.e. less flammable. These type of transformers are considered as ideal for shopping malls, hospitals, residential complexes and other commercial areas.


  • Low maintenance cost.
  • Safer option as compare to oil-filled transformer.


  • Higher operating loss.
  • Noise pollution.
  • Expensive.

Outdoor Transformers

Outdoor transformers are usually an Oil filled transformers. These transformers use oil as cooling medium and are designed to be utilized in outdoor environments due to the chance of oil leakage and spills that create a fireplace risk, and must be protected against environmental conditions.


  • Smaller and more efficient.
  • Lower operational costs.


  • High Maintenance cost.
  • Require periodic sampling of the oil.

This is all about the various types of transformer. We hope that after reading this you would gain some valuable insights and ideas out of this blog. If you still have any question you can comment in the comment section below.

One of AllumiaX's recent initiatives is a corporate sponsorship for the GeneralPAC platform which provides tutorials for power systems protection, automation and controls. Here, you will find the video series of Current Transformers. In this series they will be going over the Introduction to Current TransformersBrief Intro to Current Transformers and its ApplicationsCurrent Transformer Equivalent Circuit Model.



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