What is an Transformer? Construction, Working Principle, Types & Applications

A Transformer is a static (or) passive electrical device that transfers electrical energy from one circuit to another Circuit at the constant frequency through the process of electromagnetic induction. It is most commonly used to increase (‘Step Up’) or decrease (‘Step Down’) voltage levels between circuits.

History of Transformer

The idea of a transformer was first discussed by Michael Faraday in the year 1831 and was carried forward by many other prominent scientific scholars. However, the general purpose of using transformers was to maintain a balance between the electricity that was generated at very high voltages and consumption which was done at very low voltages.

Transformer in the simplest way can be described as a thing that converts. However, when we study more about it in-depth and in connection to electric current it is defined as a static device that changes the level of voltage between circuits. The transformer is basically a voltage control device that is used widely in the distribution and transmission of alternating current power.

Transformer Basics

Transformers are electrical devices consisting of two or more coils of wire used to transfer electrical energy by means of a changing magnetic field

Necessity of a Transformer

Usually, electrical power is generated at 11Kv. For economical reasons AC power is transmitted at very high voltages say 220 kV or 440 kV over long distances. Therefore a step-up transformer is applied at the generating stations.

Now for safety reasons the voltage is stepped down to different levels by step down transformer at various substations to feed the power to the different locations and thus the utilisation of power is done at 400/230 V.

Based on Voltage Levels

Commonly used transformer type, depending upon voltage they are classified as:

• Step-up Transformer: They are used between the power generator and the power grid. The secondary output voltage is higher than the input voltage.
• Step down Transformer: These transformers are used to convert high voltage primary supply to low voltage secondary output.

 Based on Install Location

• Power Transformer: It is used at power generation stations as they are suitable for high voltage application
• Distribution Transformer: Mostly used at distribution lanes in domestic purposes. They are designed for carrying low voltages. It is very easy to install and characterized by low magnetic losses.
• Measurement Transformers: These are further classified. They are mainly used for measuring voltage, current, power.
• Protection Transformers: They are used for component protection purposes. In circuits some components must be protected from voltage fluctuation etc. protection transformers ensure component protection.

Construction And Parts of Transformer

The three main parts of a transformer:

• Primary Winding of Transformer
• Magnetic Core of Transformer
• Secondary Winding of Transformer

• Where:
•   V_P  –  is the Primary Voltage
•   V_S  –  is the Secondary Voltage
•   N_P  –  is the Number of Primary Windings
•   N_S  –  is the Number of Secondary Windings
•   Φ (phi)  –  is the Flux Linkage

Primary Winding of Transformer

Which produces magnetic flux when it is connected to an electrical source.

Secondary Winding of Transformer

The flux, produced by primary winding, passes through the core, will link with the secondary winding. This winding also wounds on the same core and gives the desired output of the transformer.

Magnetic Core of Transformer

The magnetic flux produced by the primary winding, that will pass through this low reluctance path linked with secondary winding and create a closed magnetic circuit.

Working Principle of Transformer

Faraday’s Law of Electromagnetic Induction which states that “ the magnitude of voltage is directly proportional to the rate of change of flux.”

It’s working principle of a transformer is very simple. Mutual induction between two or more windings (also known as coils) allows for electrical energy to be transferred between circuits. This principle is explained in further detail below.

Transformer Theory

Say you have one winding (also known as a coil) which is supplied by an alternating electrical source. The alternating current through the winding produces a continually changing and alternating flux that surrounds the winding.

If another winding is brought close to this winding, some portion of this alternating flux will link with the second winding. As this flux is continually changing in its amplitude and direction, there must be a changing flux linkage in the second winding or coil.

According to Faraday’s law of electromagnetic induction, there will be an EMF induced in the second winding. If the circuit of this secondary winding is closed, then a current will flow through it. This is the basic working principle of a transformer.

Let us use electrical symbols to help visualize this. The winding which receives electrical power from the source is known as the ‘primary winding’. In the diagram below this is the ‘First Coil’.

The winding which gives the desired output voltage due to mutual induction is commonly known as the ‘secondary winding’. This is the ‘Second Coil’ in the diagram above.

A transformer that increases voltage between the primary to secondary windings is defined as a step-up transformer. Conversely, a transformer that decreases voltage between the primary to secondary windings is defined as a step-down transformer.

Whether the transformer increases or decreases the voltage level depends on the relative number of turns between the primary and secondary side of the transformer.

If there are more turns on the primary coil than the secondary coil than the voltage will decrease (step down).

If there are less turns on the primary coil than the secondary coil than the voltage will increase (step up).

While the diagram of the transformer above is theoretically possible in an ideal transformer – it is not very practical. This is because in the open air only a very tiny portion of the flux produced from the first coil will link with the second coil. So the current that flows through the closed circuit connected to the secondary winding will be extremely small (and difficult to measure).

The rate of change of flux linkage depends upon the amount of linked flux with the second winding. So ideally almost all of the flux of primary winding should link to the secondary winding. This is effectively and efficiently done by using a core type transformer. This provides a low reluctance path common to both of the windings.

The purpose of the transformer core is to provide a low reluctance path, through which the maximum amount of flux produced by the primary winding is passed through and linked with the secondary winding.

The current that initially passes through the transformer when it is switched on is known as the transformer inrush current.

Types of Transformer

The various types are described below

1. Position of the windings concerning the core
2. Core type
3. Shell type
4. According to the transformation ratio or number of turns in the windings
5. Step up
6. Step down

3. Types of services

• Power transformer
• Distribution transformer
• Instrument transformer
  • Current transformer
  • Potential transformer
  • Auto-transformer

4. On the basis of the supply

• Single-phase
• Three-phase

5. On the basis of cooling

• Air Natural (AN) or Self air-cooled or dry type
• Air Forced (AF) or Air Blast type
• Oil Natural Air Natural (ONAN)
• Oil Natural Air Forced (ONAF)
• Oil Forced Air Forced (OFAF)
• Oil Natural Water Forced (ONWF)
• Oil Forced Water Forced (OFWF)

EMF Equation of the Transformer

EMF Equation is given below

Where E₁ and E₂ are the voltages and N₁, N₂ is the number of turns in the primary and the secondary windings respectively.

Losses in the Transformer

1. Core or iron losses
2. Hysteresis loss
3. Eddy current loss
4. Copper losses
5. Stray losses

Efficiency of the Transformer

Transformer efficiency is defined as the ratio of the output power to the input power and is expressed in the equation below

Applications Of Transformer

• The transformer transmits electrical energy through wires over long distances.
• Transformers with multiple secondary side’s are used in All Electronic Devices, radio and TV receivers which require several different voltages.
• Transformers are used as voltage regulators (TV Stabilizers).

FAQs:

A Transformer is a static (or) passive electrical device that transfers electrical energy from one circuit to another Circuit at the constant frequency through the process of electromagnetic induction. It is most commonly used to increase (‘Step Up’) or decrease (‘Step Down’) voltage levels between circuits.

The various types are described below

1.Position of the windings concerning the core
2.Core type
3.Shell type
4.According to the transformation ratio or number of turns in the windings
5.Step up
6.Step down