Know about Different Types of Transformers

“TRANSFORMER”- one of the oldest innovations in Electrical Engineering. A Transformer is an electrical device that can be used to transfer the power from one circuit and another circuit without physical contact and without changing its characteristics like frequency, phase. It is an essential device in every electrical network circuitry. It consists of majorly two circuits, namely primary circuits and one or more secondary circuits. Please refer to the link Everything You Need to Know About Transformers & Working of Transformers. In this discussion, we deal with different types of transformers.

Working Principle of Transformer

The transformer working depends upon Faraday’s electromagnetic induction law. The mutual induction phenomenon between two or more winding is responsible for power transformation.

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”.

E= N dϕ /dt


E = Induced EMF


N = the number of turns

dϕ = Change in flux

dt = Change in time

Types of Transformers

There are several transformer types used in the electrical power system for different purposes, like in power generation, distribution and transmission, and utilization of electrical power. The transformers are classified based on voltage levels, Core medium used, winding arrangements, use and installation place, etc. Here we discuss different types of transformers are the step up and step down Transformer, Distribution Transformer, Potential Transformer, Power Transformer, 1-ϕ, and 3-ϕ transformer, Autotransformer, etc.

Different Types of Transformers
Different Types of Transformers

Types of Transformers based on Voltage Levels

These are the most commonly used transformer types for all the applications. Depends upon the voltage ratios from primary to secondary windings, the transformers are classified as step-up and step-down transformers.

Step-Up Transformer

As the name states that, the secondary voltage is stepped up with a ratio compared to the primary voltage. This can be achieved by increasing the number of windings in the secondary than the primary windings as shown in the figure. In a power plant, a step-up transformer is used as a connecting transformer of the generator to the grid.

Step-up Transformer
Step-up Transformer

Step-Down Transformer

It used to step down the voltage level from lower to higher level at the secondary side as shown below so that it is called a step-down transformer. The winding turns more on the primary side than the secondary side.

Step-Down Transformer
Step-Down Transformer

In distribution networks, the step-down transformer is commonly used to convert the high grid voltage to low voltage that can be used for home appliances.

Types of Transformers based on the Core Medium Used

Based on the medium placed between the primary and secondary winding the transformers are classified as Air core and Iron core

Air-Core Transformer

Both the primary and secondary windings are wound on a non-magnetic strip where the flux linkage between primary and secondary windings is through the air.

Compared to iron core the mutual inductance is less in air-core, i.e. the reluctance offered to the generated flux is high in the air medium. But the hysteresis and eddy current losses are completely eliminated in air-core type transformer.

Air Core Transformer
Air-Core Transformer

Iron Core Transformer

Both the primary and secondary windings are wound on multiple iron plate bunch which provide a perfect linkage path to the generated flux. It offers less reluctance to the linkage flux due to the conductive and magnetic property of the iron. These are widely used transformers in which efficiency is high compared to the air core type transformer.

Iron Core Transformer
Iron Core Transformer

Types of Transformers based on Winding Arrangement

Transformers based on winding arrangement are discussed below.

Two Winding Transformer

The transformers based on windings like two winding transformer includes two separate windings for every phase such as the primary & secondary. Here, the primary winding can be supplied through the input of AC whereas the secondary can be connected through the load. These two windings are isolated electrically but coupled magnetically.

The induced EMF within the secondary winding is because of the varying magnetic flux that can be caused by the changing current within the primary winding, which is also called as mutual induction. So the o/p voltage is simply because of the induction. This voltage mainly depends on the windings ratio and it can raise or lessen the input voltage.


Standard transformers have primary and secondary windings placed in two different directions, but in autotransformer windings, the primary and the secondary windings are connected to each other in series both physically and magnetically as shown in the figure below.

Auto Transformer
Auto Transformer

On a single common coil that forms both primary and secondary winding in which voltage is varied according to the position of secondary tapping on the body of the coil windings.

Transformers based on Usage

According to the necessity, these are classified as the power transformer, distribution transformer measuring transformer, and protection transformer.

Power Transformer

The power transformers are big in size. They are suitable for high voltage (greater than 33KV) power transfer applications. It used in power generation stations and Transmission substations. It has a high insulation level.

Power Transformer
Power Transformer

Different types of power transformers are autotransformers, polyphase, leakage, and resonant.

Distribution Transformer

In order to distribute the power generated from the power generation plant to remote locations, these transformers are used. Basically, it is used for the distribution of electrical energy at low voltage is less than 33KV for industrial purposes and 440v-220v for domestic purposes.

  • It works at low efficiency at 50-70%
  • Small size
  • Easy installation
  • Low magnetic losses
  • It is not always fully loaded
Distribution Transformer
Distribution Transformer

Based on different factors, types of distribution transformers are classified like mounting location, insulation type, number of phases, voltage class, and BIL or Basic impulse insulation level.

Measurement Transformer

Used to measure the electrical quantity like the voltage, current, power, etc. These are classified as potential transformers, current transformers, etc.

Current Transformer
Current Transformer

Potential Transformer

The potential transformer is also known as a voltage transformer. In this transformer, the primary winding can be connected across the HV (High voltage) line whose voltage is to be calculated, & all the instruments used for measuring & meters are allied to the secondary winding of the transformer. The main purpose of this transformer is to decrease the voltage level to a secure limit otherwise value. In this transformer, the primary winding is grounded or earthed like a security point.

The different types of potential transformers are the conventional wound type & the capacitor voltage type. As compared to capacitor voltage type, conventional wound type is expensive due to the necessity of the insulations.

Current Transformer

The current transformer (CT) is mainly used to gauge as well as also for safety. Once the current within the circuit is high to directly apply to the measuring instrument, this transformer is mainly used to change the high current into the preferred value of the current necessary within the circuit.

Current Transformer
Current Transformer

In this transformer, the main winding is connected in series toward the main supply as well as the different measuring instruments such as voltmeter, ammeter, protective relay coil, or wattmeter. These transformers include current ratio, phase relation & accuracy to allow the meter precisely on the minor side. In this transformer, the term ratio includes a huge significance in CT.

Types of Current Transformers are three types like wound, toroidal, and bar type.

Wound Current Transformer

The primary winding of the transformer can be connected in series physically by using the conductor. Here, this conductor carries the measured current within the circuit. The secondary current’s magnitude mainly depends on the transformer’s turn’s ratio.

Toroidal Current Transformer

This transformer does not include a primary winding. In its place, the line that holds the flow of current within the circuit is threaded using a hole or window within this transformer. Some of the current transformers include a split core that is used to open, close, and install & without separating the network to which they are connected.

Bar-type Current Transformer

This transformer uses the real cable otherwise bus-bar of the major network like the primary winding, which is equal to an only twist. They are completely protected from the high voltages of the system & are generally bolted toward the device which carries current.

Protection Transformers

This type of transformer is used for component protection purposes. The major difference between measuring transformers and protection transformers is the accuracy that means that the protection transformers should be accurate as compared to measuring transformers.

Instrument Transformer

Generally, an instrument transformer is called an isolation transformer or measurement transformer. This is an electrical device mainly used to change the level of voltage and current.  The main purpose of this transformer is to isolate securely the secondary winding once the primary winding has high voltage & current supply so that the energy meters, relays, or measuring instruments are allied toward the secondary winding of the transformer which will not get injured.

Instrument Transformers
Instrument Transformers

Transformers based on Phase

Transformers based on phase are discussed below.

Single Phase Transformer

It is a stationary device and the working principle of single phase transformer mainly depends on Faraday’s law of mutual Induction. At a stable level of frequency & difference level of voltage, this kind of transformer transmits AC power using one circuit to another. This transformer includes two types of windings like primary and secondary. The AC supply is provided to the primary winding whereas the load is connected to the secondary winding.

Single Phase Transformer
Single Phase Transformer

Three Phase Transformer

If the three 1-phase transformers are utilized & coupled together by using their all the 3- primary windings coupled to each other like one. All the 3- secondary windings are connected to each other like one secondary winding. So this transformer is called a 3-phase transformer. The 3-phase supply is mostly used for the generation, transmission & distribution of electric power in industries. The assembling of this transformer is not expensive and the connection of this transformer can be done through the connections of Star & Delta type.

Three Phase Transformer
Three Phase Transformer

The connection of two windings of the transformer can be done through different combinations like the following.

Primary Winding

Secondary Winding

Star (Wye)


Delta (mesh)





The above-mentioned combinations for primary and secondary windings are (Wye)-star, Delta (mesh) delta, star-delta &delta-star.

Shell Type Transformer

The structure of this kind of transformer is rectangular form & the core encloses the significant part of the two windings like primary & secondary which are arranged within one limb. The arrangement of the coils can be done by wounding in a multi-layer disc type form where the layers of this disc are insulated from each other through paper.

Berry Type Transformer

Generally, a berry type transformer is a distributed core type of shell type transformer. So, the construction of this transformer is similar to the spokes of a wheel because the magnetic core is similar to the spokes of a wheel. The arrangement of these cores is in a rectangle shape. In this type of transformer, the number of the magnetic lane in the berry type is above two that are independent because it includes the distributed magnetic lanes.

For covering the transformer, the complete structure of this can be submerged within the transformer oil and also used metal sheets which are connected tightly. The designing of metal tanks can be done particularly with a high-quality steel plate that is connected to the solid structure. After that for insulation, the transformer can be filled through the transformer oil. To avoid leakage, special care must be taken.

Oil Cooled and Dry Type Transformer

At present, there are two kinds of transformers that are mainly used like dry type and oil type transformer. A dry-type transformer utilizes air like a cooling medium whereas liquid-cooled utilizes oil. Even though both types of transformers have similar end results but there are several differences among them like maintenance, cost, noise, efficiency, recyclability, location & voltage capacities.

By considering the above-mentioned variables into account, oil type transformers are the best option. But, oil units basically cannot be utilized in any condition. The dry-type transformer is the best & several times, the necessary choice for marketable & indoor processes, as they are safer units to use around people as well as in the areas where fire exposures may occur.

Types of Transformers used in Electronics Domain

In the field of electronics, different small transformers are utilized which can be mounted on PCB otherwise fixed in the small product area. The transformers used in the electronics domain are discussed below.

Pulse Transformer

A pulse transformer is arranged on PCB that generates electrical signals within stable amplitude. This kind of transformer is used in several digital circuits wherever generation of the pulse is required in isolated surroundings. Thus, these transformers separate the primary, secondary & allocate primary pulses toward the secondary circuit, frequently drivers, or digital logic gates. Pulse transformers that are constructed properly must require stray capacitance, proper galvanic isolation & small leakage.

Audio Output Transformer

This transformer is also applicable in the electronics field. It is particularly used in the applications of audio-related wherever impedance matching is necessary. This kind of transformer handles the amplifier circuit as well as loads usually a loudspeaker. This transformer includes several coils like primary & secondary, separated otherwise center tapped.

Transformers based on the Place of Use

These are classified as indoor and outdoor transformers. Indoor transformers are covered with a proper roof like in the process industry. The outdoor transformers are nothing but distribution-type transformers.

Indoor and Outdoor Types of Transformers
Indoor and Outdoor Types of Transformers

Applications of Types of Transformers

The applications of different types of transformers include the following.

  • The power transformer is used to increase otherwise decrease voltage within a power distribution network.
  • Distribution transformer is mainly used to decrease a voltage for distribution to commercial & residential users.
  • Instrument transformer is used to decrease high voltage as well as current and after that, it can be measured & carefully used through conventional devices.
  • Single-phase transformer is frequently used to provide power for receptacle, residential lighting, AC & heating requirements.
  • A three-phase transformer is used to achieve cost-effective power distribution.
  • Autotransformers & Two-winding are normally used to increase or decrease voltage from the grids like transmission to distribution.
  • Oil cooled transformers are used in electrical substations or power distribution
  • Air-cooled transformers provide an inexpensive technique of correcting a lower otherwise higher rating of voltage to operate electrical equipment efficiently.

This is all about the different types of transformers. We hope that you might have gained some valuable insights and concepts out of this transformer article, after thoroughly reading it. Furthermore, we encourage you to share your knowledge on this particular topic or electrical and electronic projects topics as that would become a value proposition for us. However, for further details, suggestions, and comments, you can comment in the comment section below. Here is a question for you what are the types of transformers based on usage?

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