Transformer is a static device which transfer electrical energy from one voltage level to another level. It step up or step down voltage, while keeping frequency constant. So a transformer is used to change the AC voltage level. Transformers are an essential component of modern electrical systems. From powering household appliances to distributing electricity across cities, transformers are everywhere. These devices play an important role in changing the voltage levels of alternating current (AC) electricity to ensure efficient power transmission and distribution. Without transformers, power grids would be inefficient and costly, resulting in greater energy loss and higher operational expenses.

In this article, we will learn the concept of transformers, their working principles, types, advantages, and applications. The information in this article helps you extensively in your SSC JE Electrical and GATE Electrical preparation journey.

What is a Transformer?

A transformer is a static electrical device that transfers electrical energy between two or more circuits through electromagnetic induction. It works on the principle of mutual inductance to convert alternating voltages from one circuit to another without any direct electrical connection between the two circuits. A changing magnetic flux in the transformer's primary winding generates an alternating voltage in the secondary winding based on Faraday's law of induction. Transformers are mainly used to increase (step up) or decrease (step down) voltage levels without changing the frequency of the power supply.

Fig- Transformer Core

Key Features of a Transformer

• No moving parts: Transformers are static devices with no mechanical movement, which makes them more reliable and durable.
• AC Power: Transformers only work with alternating current (AC), it does not work on direct current (DC) supply.
• Magnetic coupling: Energy is transferred between coils via electromagnetic induction, without a direct electrical connection.

The working principle of transformer is based on Faraday’s Law of Electromagnetic Induction, which states that a changing magnetic field within a closed loop induces an electromotive force (EMF). In a transformer, when alternating current flows through the primary winding, it creates a varying magnetic field in the core. This magnetic field induces a voltage in the secondary winding, allowing energy transfer between the two circuits.

The fundamental structure of a transformer consists of:

• Primary winding: The coil connected to the input voltage.
• Core: Made of soft iron or steel laminations to minimize energy losses and guide the magnetic field.
• Secondary winding: The coil where the output voltage is induced.

Ideal Transformer

An ideal transformer is a hypothetical model where there are no energy losses. All the energy input to the primary winding is transferred to the secondary winding. The assumptions made for an ideal transformer include:

• Zero resistance in the windings.
• No energy losses in the core.
• Perfect magnetic coupling between the primary and secondary windings.

In an ideal transformer, all the magnetic flux produced by the primary winding is linked by the secondary winding, with no flux linkage to the exterior. It has no energy losses, and the primary and secondary turns form a closed magnetic path. The turns ratio or voltage transformation ratio of an ideal transformer is given by the ratio of the number of turns in the primary to that in the secondary. The ideal transformer's voltage, current, and power equations demonstrate a one-to-one correspondence between the input and output terminals.

The equation for an ideal transformer is:\(\frac{V_{p}}{V_{s}}= \frac{N_{s}}{N_{p}} \)

Where:

• Vp = Primary voltage
• Vs= Secondary voltage
• Np = Number of turns in the primary winding
• Ns= Number of turns in the secondary winding

Practical Transformer

In reality, all transformers experience some energy losses due to:

• Copper losses: Energy lost due to the resistance in the windings.
• Iron losses: Energy lost in the core due to hysteresis and eddy currents.
• Leakage flux: Some magnetic flux does not fully couple with the secondary winding.

The efficiency of a practical transformer is the ratio of the power output to the power input, typically ranging between 95% and 98%.

Faraday’s Law of Induction 

Faraday’s Law of Induction is the underlying principle of transformer operation. It states that the induced EMF in any closed loop is proportional to the rate of change of magnetic flux through the loop. This law can be expressed as:

\(EMF= - N\frac{d\phi}{dt}\)

Where:

• N is the number of turns in the coil.
• Φ is the magnetic flux.
• dΦ/dt is the rate of change of magnetic flux.

For a transformer, the induced EMF in the primary and secondary windings can be calculated using:

\( Ep=N_{p}\frac{d\phi}{dt}\)

\(Es=N_{s}\frac{d\phi}{dt}\)

Where Ep and Es represent the induced EMF in the primary and secondary windings, respectively.

Fig- Leakage Flux of Transformer 

EMF Equation of Transformer

The EMF equation of transformer is a fundamental concept used to describe how transformers operate. It explains how the EMF (voltage) is induced in the transformer’s coils due to magnetic flux and the number of turns in the coil. The equation can be expressed for both the primary and secondary coils of the transformer.

The general formula for the EMF induced in a transformer is:

\(E_{\mathrm{rms}}=\frac{2 \pi f N A B_{\text {peak }}}{\sqrt{2}} \approx 4.44 f N A B_{\text {peak }}\)

\(E=4.44×f×N×Φ\)

Where:

• E is the RMS (Root Mean Square) voltage,
• f is the frequency of the AC supply in hertz,
• N is the number of turns in the coil,
• Φ is the maximum flux in webers.

This equation assumes that the magnetic flux in the core is sinusoidal, which is a common assumption for general AC operation in transformers. The factor 4.44 arises from the conversion factors and the sine wave form of the changing flux.

Energy Losses in Transformer

Transformers are generally very efficient devices, but they do experience some energy losses during operation. These losses can be categorized into two main types: core losses (or iron losses) and copper losses (or winding losses). Additionally, there are other minor losses such as stray losses and dielectric losses. Here’s a detailed look at each type of loss:

Core Losses (Iron Losses)

Core losses occur in the transformer's magnetic core and are independent of the load current. They are composed of two main components:

• Hysteresis Losses: These occur due to the repeated magnetization and demagnetization of the core material as the AC current cycles. The energy is lost in the form of heat, which is proportional to the area of the hysteresis loop of the core material. This loss can be minimized by using high-quality core materials that have low hysteresis.

\(P_{\mathrm{h}} \approx W_{\mathrm{h}} f \approx \eta f \beta_{\max }^{1.6}\)

• Eddy Current Losses: Eddy currents are circulating currents induced in the conductive core of the transformer by the changing magnetic field. These currents produce heat within the core, leading to energy losses. Reducing the thickness of the core laminations, which increases their electrical resistance, can minimize these losses.
  \(\text { Eddy Current Loss }\left(\mathrm{P}_{\mathrm{e}}\right)=\mathrm{K}_{\mathrm{e}} \mathrm{~B}_{\mathrm{m}}^2 \mathrm{f}^2 \mathrm{t}^2 \mathrm{~V}\)

Copper Losses (Winding Losses)

Copper losses are the result of the resistance in the transformer's windings through which the current flows. They are directly proportional to the square of the current and thus vary with the load:

\(P_{\text{cu}} = I^2 R\)

Where I is the current through the winding, and R is the resistance of the winding. These losses increase with higher currents, so they are load-dependent.

Stray Load Losses

Stray losses are caused by stray flux that links with components within the transformer but not contributing to useful energy transfer between the primary and secondary windings. Stray flux can induce eddy currents in nearby conductive parts (like the transformer tank and other structural parts), causing additional heat and loss. These losses are generally small compared to core and copper losses but can become significant in transformers with high power ratings.

Dielectric Losses

Dielectric losses occur in the insulation material of the transformer. As the insulation is subjected to alternating electrical fields, heat is generated within the insulating material due to its dielectric properties. This loss is also relatively minor compared to core and copper losses.

Voltage Transformation Ratio

The voltage transformation ratio of a transformer defines the relationship between the primary and secondary voltages. For an ideal transformer, this ratio is directly proportional to the ratio of the number of turns in the primary and secondary windings:

\(\frac{V_{p}}{V_{s}}= \frac{N_{p}}{N_{s}}\)

If Np>Ns, the transformer steps down the voltage.

If Np<Ns, the transformer steps up the voltage.

Fig- Windings of Transformer

Types of Transformer

There are several types of transformers, each designed for specific applications. The primary types include:

1. Step-Up Transformer: A step-up transformer increases the voltage from the primary winding to the secondary winding. This is commonly used in power generation to raise the voltage for long-distance transmission, minimizing power loss.
2. Step-Down Transformer: A step-down transformer decreases the voltage from the primary to the secondary winding. These are widely used in households to reduce high transmission voltages to safer levels for appliances.
3. Isolation Transformer: An isolation transformer provides electrical isolation between the primary and secondary circuits, often used in sensitive equipment to prevent shock hazards.
4. Autotransformer: An autotransformer has a single winding that acts as both the primary and secondary windings, offering voltage regulation in applications like motor control.
5. Three-Phase Transformer: A three-phase transformer is used in power systems to convert three-phase AC voltages. These are more efficient than three single-phase transformers and are commonly used in industrial settings.

Advantages of Transformer

Transformers offer several benefits in electrical engineering and power systems:

• Efficient power transmission: Step-up transformers increase voltage for long-distance transmission, reducing energy loss.
• Voltage regulation: Step-down transformers provide safe voltage levels for appliances.
• Electrical isolation: Isolation transformers protect equipment and personnel from electrical shocks.
• Cost-effective: Transformers help reduce the cost of power generation and distribution.

Disadvantages of Transformer

While transformers are essential, they do have some drawbacks:

• Size and weight: Large transformers can be bulky and heavy, making transportation difficult.
• Energy losses: Even though transformers are efficient, they still experience losses due to copper and iron losses.
• High cost: High-quality transformers can be expensive to manufacture and install.

Applications of Transformer

Transformers have a wide range of applications in both industrial and residential settings. Here are some key uses:

• Power generation and distribution: Step-up and step-down transformers are important in the transmission of electricity from power plants to homes and businesses.
• Electrical appliances: Transformers regulate voltage levels for devices like refrigerators, televisions, and computers.
• Medical equipment: Isolation transformers provide safe and reliable power for sensitive medical devices.
• Industrial machines: Three-phase transformers supply power to heavy industrial machinery, motors, and compressors.

Conclusion

The transformer is a fundament of modern electrical engineering. Whether it’s stepping up voltage for efficient power transmission or stepping it down for safe usage in homes, electrical transformers are critical for ensuring the smooth operation of power systems worldwide. Understanding the working principle of transformers, types, and their applications is vital for students and professionals in electrical engineering.

This article concludes all the information related to Transformer, which helps to propel your preparation for various AE/JE examinations. To boost your preparation, you should test yourself through a series of Mock Tests for Electrical Engineering Exams. You can check the syllabus for the AE/JE exam. You can visit the Testbook app to keep yourself updated with all the exam-oriented information related to the upcoming examinations, including GATE Electrical, SSC JE, ESE, RRB JE, and state AE/JE Electrical exam.