# Types of Transformer (Categories Wise) – Working and their Applications

Most people thought that there are only two types of Transformer— step-up and step-down transformer then for sure, you have no idea what the total numbers are.

There are majorly 17 types of transformers that serve our life. All these have their own ways of working schemes. To invade this broad topic in a crisp way, we categorized all transformer types into 6 broad categories.

All the information that is listed in the post is intended both for the general purpose and also to help the academic students in learning.

But, before jumping directly to the types of the transformer, let’s discuss in short, “What is a Transformer?”.

## What is a Transformer?

A transformer is a passive static device that uses the process of electromagnetic induction to transfer electrical energy from the primary source to the secondary source(s). Factually, all the transformers that are based on electromagnetic induction only work with A.C. current.

And the most common types of transformers are power transformers that constitute step-up and step-down transformers.

### Working Principle of Transformer

Mutual Induction— the working principle of a transformer. So, when an AC source induces current to the primary coil, the alternative current produces varying magnetic flux in the core of the transformer.

The resultant values lead to the production of varying electromotive force (emf) to the secondary coil. Hence, the conversion takes place.

In the majority of cases, the number of turns and thickness of the winding coil at each end is the determining factor. In addition, there might be a case where a transformer has more than one secondary coil.

The law that dictate the working of a transformer is Faraday’s law of induction. It was discovered in 1831. It states two major laws of induction; 1st law describes the induction of emf while the second law quantifies the emf produced in the conductor.

## Types Of Transformer— Category-Wise List

The following are broad types of the transformer which are subdivided individually based on common concepts (or working concepts).

1. Transformers Based on Voltage Levels
• Step-Up Transformer
• Step-Down Transformer
2. Transformer Based on the Core Medium
• Air-Core Transformer
• Iron Core Transformer
• Ferrite Core Transformer
• Toroidal Core Transformer
3. Transformers Based on Winding Arrangement
• AutoTransformer
• Variable autotransformer
4. Types of Transformers based on Usage
• Power Transformer
• Distribution Transformer
• Measurement Transformer
5. Types of transformer based on Phases
• Single Phase Transformer
• Three Phase Transformer
6. Types of Transformers used in Electronic Appliances
• Pulse Transformer
• Audio Output Transformer

### Types of Transformers based on Voltage Levels

These types of transformers depend on the ratio of the voltages in the primary and the secondary winding. These are also the most common type of transformers which are employed in power transmission. This is why they are the backbone of the power distribution system.

These are the following two types of voltage level transformers;

#### A. Step-Up Transformer

A Step-up transformer works to convert the low voltage into high voltage values. In addition, it also serves to convert the high values of current into low ones.

In a step-up transformer, the number of turns at the primary coil is less than the secondary coil. Hence, on the induction of current from the primary coil, the voltages are step-up with corresponding lower values of current.

Step-up transformers are generally seen in electrical transmission and power distribution lines. In addition, some electric motors, X-Ray machines, and stabilizers also have a step-up configuration.

For more details on the step-up transformer, you can visit our dedicated post on Step-Up Transformer: Principle, Construction, Advantages, and More.

#### B. Step-Down Transformer

It has the same model of a step-up transformer but with fewer coil turns at the secondary end as compared to the primary. And that’s what makes it the opposite of a step-up transformer.

In the step-down transformer, the elevated primary source voltage is step-down due to less emf force which is generated at the secondary coil (because of fewer turns).

So, you can say that if you switch the source AC to the secondary part of a step-up transformer, it starts working as a step-down transformer.

The primary use of a step-down transformer is for the conversion of high transmission lines voltages into home voltage (230/120 V). Other common uses are in appliances such as televisions, inverters, voltage stabilizers, etc.

### Types of Transformer based on the Core Medium

As per the name, the core material is the determining factor for these transformers. The reason is the different core mediums produce different intensities of magnetic flux. These are the most common types of core transformers that differ by their core medium.

#### A. Iron Core Transformer

Iron core transformers have a laminated core of iron plates that are usually heavier in weight and compact in size. These thin and multiple plates are punched to form the core which provides less reluctance.

In this, there are multiple soft iron plates—that have an excellent design— provide a reliable magnetic flux. The iron plates are tune-up to the material level because of some additional metals (in a small amount). This all eventually makes it an efficient transformer.

However, as there is no cooling material and has a compact size, they produce a higher amount of heat. Therefore, a consistent air-flow system should be employed, in case, there are multiple iron core transformers (in a smaller area).

While talking about the various shapes, these soft plates are available in ‘E’, ‘I’, ‘U’, ‘L’, etc. form. Due to compact size, they are generally the component of small appliances such as video-game stations, galvanometers, AC stabilizers, cooling systems, etc.

#### B. Ferrite Core Transformer

Ferrite Core Transformer has a high magnetic permeability relative to the regular soft iron plate transformer. The core of ferrite transformers is a combination of a homogeneous ceramic mixture of iron oxide (Fe2O3) along with oxides or carbonates of manganese, zinc, nickel, or magnesium.

In this type of transformer, due to less flux density, there are less eddy current losses. They usually have an ‘E’ shaped ferrite core that holds the primary and secondary coils at each end.

Like iron core transformers, they are also available in different shapes and sizes which are obvious, based on the application requirements. The most common shape in the ferrite core transformer is E core.

All of this adds up to form high-frequency operational usage. And that’s the reason why ferrite core transformers don’t require a laminated core.

Therefore, these transformers are commonly used in high-frequency appliances like Switched-Mode Power Supply (SMPS), Radio Frequency application, etc.

#### C. Air-Core Transformer

No Base Core— only air that separates both coils. Are you using any wireless charging phone? If yes, then it is what air-core transformers are all about.

For example, consider that your mobile has a secondary winding and your charger has a primary winding. Therefore, when you place your phone over the charger, it starts charging your phone.

So, in the air-core transformer, both the primary and secondary coil has a separate compartment. And when the primary coil induces current it produces emf. Hence, when the secondary coil is brought closer to the primary coil then it starts to power the load.

However, due to the absence of a real core, magnetic flux is less. Though it makes the air-core transformer lighter in weight. Apart from wireless charging, they a major part of Radio Frequency (RF) appliances.

#### D. Toroidal Core Transformer

They have a donut-shaped toroidal ring core. The toroidal ring can be made from iron or ferrite core which is widely used to make a superior functional movable model.

The ring core serves a major purpose i.e. less leakage of inductance and eventually offers a very high inductance. However, they usually have a compact design which makes it relatively less weighty than other same rating transformers.

The construction cost of these toroidal transformers is much higher than the iron core transformers because of the slow and complex process of winding on the donut-shaped core.

### Types of Transformer on the Basis of Winding Arrangement

These transformers are classified on the basis of the winding arrangement of the primary and secondary coil in a single-coil system. There are two types of winding-based transformers— auto and variable autotransformers.

#### A. Auto-Transformer

Unlike std. transformers that have two separate windings that run in different directions. But in autotransformers, only have one binding coil that has the primary and secondary coil which are separated by a tapped position.

And the tapped position is the key factor for the variation of the output voltage. So, when the AC voltage is supplied to the primary part, a lower (or higher) voltage is induced on the secondary position.

But, there is a big drawback — the corresponding power rating of the autotransformer is smaller than the actual-load power rating. But subsequently, the price of the autotransformer is lower. Other advantages— they are light, small, and more efficient than traditional two coil transformers.

However, you can encounter 3-Phase autotransformers which cast-offs in the high voltages power distribution lines.

#### B. Variable Auto-transformer

If you call it the derivative of the autotransformer then it sounds true. Because a minor adjustment makes it a completely different transformer that allows wide variable values of the output voltage.

Generally, on the secondary region, a sliding carbon brush is attached which can slide on the secondary coil as per the requirement. This will give a flexible approach to an appliance (transformer) to produce a wide variety of voltage values.

The main use of these types of transformer is to test the working of other appliances and also as a voltage regulator.

### Types of Transformers Based on Usage

Transmission lines and power distribution grids use different types of power transformers, which usually have three-phase systems. These are the following three types of transmission transformers;

#### A. Power Transformer

Power Transformer is gigantic and is suitable to transfer high voltages (usually greater than 33 kV). You can easily recognize them in power generation and transmission systems, because of their greater size. At transmission systems, to minimize the power loss, power transformers convert low voltage-high current to high voltage-low current.

In addition, their structure has a highly insulated core with a high insulation level that boosts the voltages to such a high value. And that’s why they need a very reliable cooling system which in general, uses coolant liquids (oils).

Specifically, power transformers are the bridge that connects the power generator to the transmission lines and distribution grid. It usually deals in 33 kV power output, but there are other variants of power transformers that can even generate  400 kV, 200 kV, 110 kV, and 66 kV.

One of the most important facts about power transformers is their larger size and engineering concepts invades the maximum efficiency, which is close to 100%. Apart from this, a power transformer has one more function— they reduce the power fluctuations at the transmission network.

#### B. Distribution Transformer

A distribution transformer is a smaller replica of a power transformer. They are usually part of sub-levels of distribution grids.

While talking about its construction, the primary coil has enamel-coated copper wire along with moisture-free-insulated coolant oil. On the other hand, the secondary end has a low voltage winding. Hence, typically, distribution transformers are step-down transformers.

Unlike power transformers, they deal with lower voltages values such as 11 kV, 6.6 kV, 3.3 kV, 440V, and 230V. So, as the distribution grid became smaller and smaller, their conversion rates stepped down, to the last value of 230V (consumer level).

#### C. Measurement Transformer

The name states its working. The measurement Transformer has a large cylindrical structure that has the sole purpose of measuring the various parameters of electricity.

So, a measurement transformer can dictate the flowing voltages, current, power metrics, etc of a connected line. Therefore, they act as an additional check to have a close look at fluctuation and power drop levels.

However, on the basis of their measuring parameters, majorly has two types; potential and current transformers.

##### a. Potential Transformer (PT)

In potential transformers, the voltages are first reduced to low levels of voltages. This is because they are generally employed in transmission lines and distribution grids where the voltages are too high.

So, they use a step-down process to cut down the too-high voltage values to a safer level to measure. This is all done by the potential transformer itself. So, there is no external step-down transformer is used to reduce the voltages values.

##### b. Current Transformer (CT)

Disclaimer- No relation of CT with CT scan. By definition, a current transformer is a transformer that checks the reduction or multiplication of the AC source to evaluate the values in amperes.

Like a potential transformer, it also reduces the voltages parameter down to measure. However, this time the current is measured through the attached ammeter.

So, you can call it an instrumental transformer that’s sole purpose is to measure the proportional current values in their primary (input) coil.

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### Types of Transformer Based on Phases

Throughout the world, there are basically two types of appliances. One is a single phase and the second is multiple-phase (two-phase and three-phase), so are the transformers. Therefore, there are two types of phase transformers; single-phase and three-phase transformers.

#### A. Single Phase Transformer

These are simple transformers that usually have step-down configuration and also follow the same principle of Faraday’s law of mutual induction. In this transformer, a single-phase alternating current induces a steady output voltage.

Low-end appliances such as mixer-grinders, music stations, etc. use single-phase transformers.

#### B. Three Phase Transformer

A three-phase transformer has a separate primary and secondary winding for each phase. You can say that if three single-phase transformers are combined they form a three-phase transformer. In addition, it is less costly than buying three individual single-phase transformers.

However, in the majority of cases, to maintain a steady voltage supply, secondary windings combine to form one. And the whole system is called to be a three-phase transformer.

In general, a three-phase transformer can have a star and delta type of connections. And the possible combination would be star-star, delta-delta, star-delta, delta-star for primary and secondary winding, respectively.

They are usually the part of heavy-duty appliances of industrial areas, power generation, transmissions, and distribution systems.

### Types of Transformers on the Basis of their Applications

There is a vast variety of electronic appliances that uses a transformer. But majorly, we discuss two types of instrument transformer, one is pulse transformer and the second is the audio output transformer.

#### A. Pulse Transformer

When electrical pulses are required at constant amplitude, a pulse transformer would be the only option. A pulse transformer optimizes the transmitting electrical pulses with a constant amplitude.

Majorly, a pulse transformer uses a low value of leakage inductance which makes it more distortion sensitive. In addition, the primary pulses before passing to the secondary circuit, are transferred through logical gates to get the desired pulse rate (with constant amplitude).

However, after every use, the pulse transformer must be ‘dumped’ before using it for next time.

They are one of the most vital appliances, from small PCB mount to military-grade applications. In general, PCB mounted transformers works to compute digital logic and telecommunication signals.

They also serve the crucial conceptual functions in medium-sized appliances, such as camera flashes. In addition, the military utilizes pulse transformers in its radar system, particle accelerators, and other high pulse-based devices.

#### B. Audio Output Transformer

They serve many functions in audio devices. But in general, audio output transformers are used in audio circuits to carry audio signals. However, they are a wonderful tool to remove the interference in terms of DC components also from other radio frequencies.

Other than this, they can block certain radio frequencies, split or combine audio signals, and performs impedance matching (between loudspeaker and amplifier).

They usually have higher current and voltage than other audio appliances such as microphones and line-leveler. Audio output transformers can also act as bridges to connect 2-wire and 4-wire communication.

## General FAQs

Q.1 What are the core type and shell-type transformer?
Ans.
Core type transformer has both the winding which is sidely placed. Whereas, in the shell transformer, the windings are centrally aligned on the central limb.

Q.2 What are the two main types of transformer?
Ans.
In broad, there are step-up and step-down transformers which could be a power transformer, distribution transformer, single-phase transformer, a three-phase transformer, a potential transformer, and the list goes on and on.

Q.3 How the ferrite core is made?
A ferrite core is made from the homogeneous mixing of iron oxide along with oxides and carbonates of nickel, zinc, and manganese. Then they are molded in customizable plates at 1300o C.