Electrical Machines Tutorial

Electrical Machines are electromagnetic devices designed to convert electrical energy into mechanical energy and vice-versa. Electrical machines are studied as a core subject in the electrical engineering discipline. It is included in the syllabus of electrical engineering to understand the design, principle, operation, and applications of various electrical machines like generators, motors, transformers, etc. which are very important for electrical engineers.

Electrical machines are the fundamental components of modern engineering and industries. In the domain of electrical engineering, it is very crucial to master the concepts of electrical machines because they pave the path for power generation, operation of machinery, and energy conversion.

This tutorial on electrical machines is written at a somewhat basic level and is intended for those who do not necessarily have a background in electrical engineering and electrical machines. Thus, it may be used as an introductory resource on electrical machines for undergraduate college students as well as a reference for practicing electrical engineers.

What are Electrical Machine?

An electrical machine is an electromagnetic device that either converts electrical energy into mechanical energy (electric motor) or converts mechanical energy into electrical energy (electric generator).

A transformer is a special electrical machine that does not covert electrical energy into mechanical energy and vice-versa, instead it transforms the voltage levels of electrical energy. The operations of all electrical machines are based on the mutual interaction of electric and magnetic fields. Hence, they are called electromagnetic machines.

Electrical machines can be classified into various types depending on their functions, supply used, for example, induction motor, synchronous motor, transformer, dc motor, dc generator, alternator, etc.

Types of Electrical Machines

Electrical machines can be classified into various types. The detailed main types of electrical machines is shown in the following figure.

Outline of This Tutorial

The main objective of Electrical Machines is to provide an overview of the range of concepts of electrical machines, and principle and applications of various electrical machines. The understanding these concepts is very important to perform jobs related to electrical machine design, operation, and maintenance.

This tutorial on "Electrical Machines" is divided into six modules −

The first module covers the basic concepts related to electrical machines that includes topics like principle of −

The second module covers the theory of electrical transformer like −

Electrical Transformer
Construction of Transformer
EMF Equation of Transformer
Turns Ratio and Voltage Transformation Ratio
Ideal and Practical Transformers
Transformer on DC
Losses in a Transformer
Efficiency of Transformer
Three-Phase Transformer
Types of Transformers

The third module covers the concepts of DC machines such as −

The fourth module covers the concepts related to induction motors like −

The fifth module explains the synchronous machines including its −

The sixth module of this tutorial provides useful resources, a quick guide, and community discussion platform on electrical machines.

What does an Electrical Transformer Do?

An electrical transformer increases or decreases the voltage levels in an electrical power system. A transformer that increases the voltage level (i.e., output voltage is greater than input voltage) is known as a step-up transformer. A transformer that decreases the voltage level (i.e., output voltage is less than input voltage) is known as a step-down transformer.

Working Principle of a Transformer

An electrical transformer works on the principle of mutual inductance. The principle of mutual inductance states that when two electromagnetic coils are brought near to each other such the magnetic field produced by one coil links with the other. If this linked magnetic field produced by first coil changes, then it induces an EMF in the second coil. This principle is highlighted in the following figure.

Are transformers AC or DC?

Transformers are AC devices. An electrical transformer cannot operate on DC supply because transformer requires changing magnetic flux for its operation which can be only produced by AC supply.

Types of Electrical Motor

An electric motor is an electromechanical energy conversion device that converts electrical energy into mechanical energy. Electric motors can be classified into various types as follows −

1. DC Motors

Those electric motors that convert direct current electricity into mechanical energy are known as DC motors. DC motors are further classified into the following types −

DC Series Motor − A DC motor in which armature winding and magnetic field winding are connected in series with each other is called a DC series motor.
DC Shunt Motor − A DC motor in which armature and field windings are connected in parallel with each other is called a DC shunt motor.
DC Compound Motor − A DC compound motor is one which consists of both series and shunt field winding is called a compound DC motor. There are two types of compound DC motors, which are −
- Cumulatively Compound DC Motor − When shunt and series fields assist each other, then the motor is called a cumulatively compound dc motor.
- Differentially Compound DC Motor − When the shunt and series fields oppose each other, then the motor is called a differentially compound dc motor.

2. AC Motors

Those electric motors that require alternating current supply to produce mechanical energy are called AC motors. There are two main types of AC motors namely,

Induction Motor − An induction motor is a type of AC electric motor that operates on the principle of continuous electromagnetic induction. Induction motors can be classified as single-phase induction motors and three-phase induction motors.
Synchronous Motor − A synchronous motor is also a type of AC motor that operates on the principle of magnetic locking, where the rotor is locked with the stators rotating magnetic field and rotates at the synchronous speed (i.e., speed of rotating magnetic field).

Prerequisites to Understand Electrical Machines

As with most introductory electrical machine tutorial, the main prerequisites are a basic understanding of physics and mathematics. However, it will definitely help if you are familiar with the fundamental concepts of electric and magnetic circuits.

FAQs on Electrical Machines

We have collected here a set of Frequently Asked Questions (FAQs) on Electrical Machines, followed by their answers.

The main function of an electric motor is to convert input electrical energy into rotational mechanical energy and drive mechanical loads.

An electric generator is an electromechanical energy conversion device that converts mechanical energy into electrical energy. The output of an electric generator is electric supply that can be either AC or DC, depending on the type of generator.

The main function of a generator is to produce electricity. In other words, an electric generator performs the conversion of mechanical energy into electrical energy.

An electric generator produces electricity through electromagnetic induction. A generator consists of an armature winding and a rotating magnetic field winding. When the magnetic field of rotating winding links to the armature winding (stationary), due to rotation, the magnetic field linked to the armature winding changes

According to the principle of electromagnetic induction, an EMF is induced in the armature winding. This induced EMF causes a potential difference at the ends of the armature winding. This is how a generator produces electricity.

It depends on the type of generator, i.e., a generator can generate AC as well as DC.

The generator that produces alternating current output is called an AC generator. The generator that generates direct current electricity is called a DC generator.

Alternator is nothing but an electric generator that produced alternating current electricity. Therefore, the main function of an alternator is to produce AC electricity.

A synchronous machine, either motor or generator, is a rotating electrical machine whose rotor rotates at the same speed as the rotating magnetic field do, i.e., synchronous speed.

If the machine is a generator, then it is called a synchronous generator. If the machine is a motor, then it is referred to as a synchronous motor.

Synchronous and asynchronous machines are the types of rotating electrical machines used for electromechanical energy conversion.

A synchronous machine is one that operates at the synchronous speed (i.e., speed of the rotating magnetic field), while an asynchronous machine is an electrical machine that can never operate at the synchronous speed but always runs at a speed slightly lower than the synchronous speed. Asynchronous machines are also known induction machines.

An induction motor is said be an induction motor because it requires continuous electromagnetic induction for its operation. If electromagnetic induction dies in the motor, the motor stops instantly.

The working principle of induction motor is based on the principle of electromagnetic induction and interaction of electric and magnetic field. According to these principles when a rotating or changing magnetic field links to a conductor, an EMF is induced in the conductor.

If the conductor is in a closed circuit, an electric current start flowing through it. Now, the current carrying conductor is located in a magnetic field and experiences an electromagnetic force and moves in a certain direction.

A rotating electrical machine is nothing but an electromechanical energy conversion device that consists of two parts namely, stator and rotor. It is called a rotating electrical machine because its rotor is free to move or rotate on its own axis. Electric generators and motors are known as the rotating electrical machines.

An electrical transformer is used for the following purposes −

To increase or decrease the voltage levels in power system.

To provide electrical isolation between two electric circuits.

To provide magnetic coupling between two electric circuit.

For measurement and protection purposes in high-voltage power networks.

A singly excited motor is a type of electric motor in which only a single coil is used to produce magnetic field. Thus, a singly-excited motor consists of only one electrical input and one mechanical output. A common example of singly-excited motor is an induction motor.

A doubly-excited motor is a type of electric motor which consists of two separately excited coils to produce magnetic fields. Hence, in a doubly-excited motor, there is two electrical inputs and one mechanical output. A common example of doubly excited motor is a synchronous motor.

Print Page