Transformers: History, Basic Principle, Construction, Working Mechanism, Types and Applications

Table of Contents

Introduction to Transformers

Transformers are the devices for setting electrical energy between two or more circuits. It works on the basis of the principle of electromagnetic induction. Its main use is to increase (step up) or decrease (step down) voltage levels in power systems also keeping frequency the same. Transformers allow smooth transmission of electricity over a long range of distance. They have become a reliable source in the field of electricity transmission and is one of the major supporting components in modern electricity and engineering.

Almost every aspect of electrical power distribution is driven by transformers. Electricity generated at power plants is usually at lower or medium voltage level, but to transport it efficiently over long distances, it must be increased to very high voltages. Later, to supply it through households, offices, and industries, the voltage is again decreased or stepped down to safer levels. Without transformers, there would be greater loss in the power transmission and hence the efficiency in the output. Thus, transformers have made our basic level energy supply to a larger scale supply, efficient.

Unlike motors, generators or dynamo, transformers are simple, static machines and do not have moving parts like rotors. This simple nature of themselves makes them reliable, durable, cost-friendly and take low maintenance requirements. However, their working mechanism and functioning are some special processes that require precise engineering. This is also required to ensure efficiency and safety in the transmission..

Historical Development of Transformers

After the discovery of Faraday’s law of Electromagnetic induction, George Westinghouse got interested in electricity. He immediately and accurately decided that Edison’s low voltages were not suitable for large-scale transmission. He also thought that long-distance transmission could be made possible with high voltage. Further, the technology would be cost-effective and easier only for alternating current. He also found that transformers would be a major takeover of alternating current over direct current in transmission and distribution systems.

Pavel Yablochkov conducted the first transformer-like experiments in the 1870s, using induction coils to power the arc lamps. Later, in 1882, Lucien Gaulard and John Dixon Gibbs built the first practical transformer model with an open iron core. However, the design had some restrictions due to huge losses in delivery and low efficiency.

Later, in 1885, William Stanley while working with George Westinghouse, invented the first cheaper and applicable transformer with a closed iron core. This was found to significantly increase efficiency. Thus, it was a breakthrough in power supply and critical during the conflicts seen in the concepts of power transmission. The alternating current (AC) promoted by Nikola Tesla and Westinghouse challenged the direct current (DC) pushed forward by Thomas Edison. DC was not that efficient to transfer power over long distances and hence AC gained a great applause.

Transformer technology is continuously progressing from the day of its discovery i.e. from oil-cooled to dry-type, from tiny networking units to huge transformers used for high-voltage transmission networks. The history of transformers leaves a global imprint of the unrecognizable ability of AC configuration over DC.

Basic Principle of a Transformer

As mentioned above, the fundamental working principle of a transformer is the same electromagnetic induction. When alternating current flows through the primary winding, it produces a magnetic field that varies with time. This magnetic field is directly linked with the secondary winding at the laminated magnetic core. This induces an EMF in the secondary winding.

Mathematically, Faraday’s Law can be written as:

E=−NdΦ/dt [Equation 1]

Where:

E = induced EMF
N = number of turns in the winding
Φ = magnetic flux

The ratio of voltages across the primary and secondary windings is proportional to the ratio of turns:

V1/V2=N1/N2 [Equation 2]

Here, V1 and V2 are the primary and secondary voltages. N1 and N2 are the number of turns in the primary and secondary windings.

This mathematical relation shows that the voltage in a transformer can be to step up or step down, without changing the frequency.

Transformer Construction

The construction of a transformer is not that complex. Typically a transformer has following major parts:

Core – It is made up of a laminated silicon steel sheet so as to reduce eddy current losses. The core provides a direction for the magnetic flux.
Primary Winding – It is connected to the input supply. Its major role in the circuit is to create a magnetic field when AC flows through it.
Secondary Winding – It gives the output to the load. It functions on receiving the induced voltage from the primary winding through mutual induction.
Insulation – It is for the safe operation of the circuit. It ensures that the electrical windings are properly insulated and prevents short circuits.
Transformer Oil (for oil-filled types) – It provides cooling and insulation to the load in the circuit and prevents thermal effects from overheating.
Tank – It encloses all the bodies like the core, windings, and insulating oil.
Bushings – It provides insulation to the terminals for connecting external circuits.
Cooling System (For liquid and gas based system) – It is added to the system to prevent overheating. Radiators, fans, or pumps are added for large power transformers.
The construction of a cooling system may differ with the type of transformer: small dry-type transformers use air cooling, while large transmission transformers use oil-immersed designs.

Working Mechanism: Electromagnetic Induction in Transformers

When AC voltage is given to the primary winding, current flows through it. The current produces a fluctuating magnetic field in the core. The changing magnetic flux interacts with the secondary winding. This induces an alternating voltage in the secondary winding and hence current is induced.

If the number of turns in the secondary coil is greater than the primary, the transformer is a step-up transformer and results in increasing voltage.
If the number of turns in the secondary coil is lesser, it becomes a step-down transformer and results in decreasing voltage.

Transformers are based on mutual induction; therefore, the whole working and the output depends on the flux linkage between the primary and secondary windings. That is why high-quality magnetic cores should be used and leakage flux should be kept minimum.

Types of Transformers: Step-Up, Step-Down, and Special Types

The various types of transformers are:

Step-Up Transformer – It is used to increase voltage and has more no. of turns on the secondary coil than in the primary coil. It is used in transmission lines.
Step-Down Transformer – It is used to decrease voltage and has lesser turns in the secondary coil than in the primary one. It is used in distribution systems and electronic devices.
Power Transformer – They are used in large units for transmission networks. They are specially rated above 200 MVA.
Distribution Transformer – They are smaller units supplying electricity to households and industries.
Instrument Transformers – They are used in instruments for measurements like current transformers (CTs) and potential transformers (PTs).
Isolation Transformer – It provides electrical isolation without affecting the voltage.
Autotransformer – It is built as a cost-effective transformer which uses a single winding to act as both primary and secondary coil.
Three-Phase Transformer – Three-phase power systems use a single unit or an array of three single-phase transformers.

Ideal vs. Practical Transformers

Ideal Transformer: An ideal transformer is assumed to experience no loss and provide 100% output. Thus, it has a perfect flux linkage, and 100% efficiency. It is a theoretical model and is impossible to attain it practically. It is only used for theoretical analysis.
Practical Transformer: Real transformers experience some losses such as copper losses, core losses, and leakage flux. These losses reduce the efficiency of the transformer. The loss can be minimized by using high-grade and laminated alloys of magnetic substances or good cooling systems. Engineers compensate for these losses while designing the devices and applications.

The efficiency (η) is calculated as:

η=Output Power/Input Power×100%

Modern transformers are constructed to obtain the efficiency above 98%..

Transformer Losses and Efficiency

Transformers suffer from various losses and hence the output is decreased. The losses are as follows:

Iron Losses – It includes hysteresis loss due to continuous magnetization and demagnetization of the core and eddy current losses in the core.
Copper Losses – It occurs due to the resistance in windings which is proportional to I^2R.
Leakage Flux Losses – It is due to the improper coupling between primary and secondary coils.
Stray Losses – It is a minor loss occurring due to the flux leakage that induces currents in nearby metallic parts.

Cooling and Insulation Methods in Transformers

Transformers generate heat due to losses. This can damage the circuit. So it must be controlled to prevent damage. Cooling methods are:

Air Natural– Small dry-type transformers can be cooled naturally by air.
Air Forced (AF) – Fans are used to provide rapid cooling in some simple transformers. This increases the cooling rate and makes the transformer capable to withstand higher loads compared to natural air cooling
Oil Natural Air Natural (ONAN) – TIn oil-based transformers, the windings and core are bathed in mineral oil. The oil absorbs heat and rises to the surface, while colder oil sinks, creating natural heat transfer. Heat is subsequently released to the surrounding air by radiators.
Oil Natural Air Forced (ONAF) – They are similar to ONAN with a little upgraded version. Cooling fans are used to blow air over the radiators to increase the heat loss. This approach is used on medium to big transformers.
Oil Forced Air Forced (OFAF) – Oil pumps flow insulating oil, while fans push air across radiators. This approach effectively cools huge power transformers.
Oil Forced Water Forced (OFWF):
Pumps transport oil through heat exchangers, where water absorbs heat. This is highly effective and is utilized in huge transformers such as power plants.

Insulation methods

Solid Insulation:
Materials such as paper, pressboard, varnish, and epoxy resin are used to insulate windings and core laminations.
Liquid Insulation (Mineral Oil):
Transformer oil acts as both an insulator and coolant. It fills the spaces between windings and the core, preventing partial discharge.
Gas Insulation:
In some special transformers, inert gases like sulfur hexafluoride are used for insulation. These provide excellent dielectric strength and prevent oxidation.
Modern sunstainable Insulation:
Recently the use of biodegradable natural esters and synthetic oils are increasingly used. They are found to be safer for the environment and provide better fire resistance compared to mineral oils.

Applications of Transformers in Power Systems and Industry

Electric Power Transmission and Distribution – Stepping up generation voltages for transmission and stepping down for end-users.
Electronics – Low-power transformers supply correct voltage levels for devices.
Measurement and Protection – CTs and PTs ensure safe and accurate monitoring of high-voltage systems.
Industrial Applications – Welding transformers, furnace transformers, rectifier transformers.
Renewable Energy Systems – Solar inverters and wind turbines require transformers for grid integration.

Advantages and Limitations of Transformers

Advantages:

High efficiency (95–99%)
Simple construction with no moving parts
Reliability and longevity
Capable of handling a wide range of power levels
Essential for the transmission of power in long-range

Limitations:

Operates only with alternating current and does not work with the direct current.
Load increases with power rating and hence efficiency may decrease
Cooling and insulation may be complex for larger power systems
Step up/ down voltage regulation may be affected by heavy loads
Sensitive to harmonics and overloading

Future Trends and Innovations in Transformer Technology

Transformer technology is evolving rapidly and conquering the challenges of modern power systems: Some future works can be performed as follows:

Smart Transformers: They work with sensors and communication systems for the voltage regulation and hence power transmissions in smart grids.
Solid-State Transformers (SSTs): They use power electronic devices and super conductors instead of conventional magnetic cores. They offer a portable and better power control.
Eco-Friendly Insulation: Conventional mineral oils have been replaced with environment friendly and degradable natural esters.
High-Temperature Superconducting (HTS) Transformers: They are designed to provide minimum losses with compact designs.
Integration with Renewable Energy: They are specially designed for automobiles, EVs, solar and wind systems.
Multitransformers: A new technology of connecting several transformers in a circuit has been developed for more efficient work covering even larger distances.

Conclusion

Transformers are the most dependable and durable power sources working with AC. Although they have no connection with the DC, they are still popular with their simple construction and long range power covering ability. They have been adopted for the rural home appliances to the most powerful power plants. Their working is fully related with Faraday’s law of electromagnetic induction. Ever since their discovery, they have become an inseparable part in electricity and engineering. The evolving technologies are even working harder to minimize losses in power transmission, keeping their size compact. Thus, they are the backbone of all home to industrial and research purpose power production.

References

Lebedev, V. (2007, October). Transformer basics. In 2007 Electrical insulation conference and electrical manufacturing expo (pp. 356-359). IEEE.

Del Vecchio, R., Del Vecchio, R. M., Poulin, B., Feghali, P., Shah, D., & Ahuja, R. (2017). Transformer design principles. CRC press.

Werle, P., & Brendel, H. (2021). Transformers. In Springer Handbook of Power Systems (pp. 443-509). Singapore: Springer Singapore.

Ip, V., & Is, V. (2007). 7.2 Transformer Basics. Electric Power Transformer Engineering.

Mikail, R. (1803). Fundamentals of electric motors and transformers. Bangladesh University of Engineering and Technology, Dhaka, Short Course, 984-32.

https://en.wikipedia.org/wiki/Transformer

https://www.geeksforgeeks.org/physics/transformer/