Electrical Machines

A Practical Approach

Satish Kumar Peddapelli, Sridhar Gaddam

• Publisher: De Gruyter
• Year: 2020
• Print ISBN: 9783110681956
• eBook ISBN: 9783110682441
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Automation in Engineering
• Index: Technology & Engineering

Electrical Machines covers the theoretical and mathematical concepts of the most commonly used electrical machines in industry and home appliances. This book presents the practical usage and functioning of electrical machines in a way which is easily understandable by the readers. It provides a different approach from other books and presents a step by step procedure on how to start and run the machine on various load, operating, and testing conditions and connections. It also presents a complete set of readings, calculations, and graphs/plots performed on standard electrical machines with rated voltage and current. Each chapter contains answers to questions related to particular machines and testing conditions/operations, solutions to numerical problems, and some exercise problems for practice.

1 DC Generators

1.1 Introduction

A machine that changes mechanical power into electrical power by using the principle of magnetic induction is called generator. Whenever a conductor cuts the magnetic field, an emf(Electromotive Force) is generated in that conductor. The magnitude of the generated emf is proportional to dϕ/dt and the polarity depends on the direction of the flux and the conductor. Fleming’s right hand rule is used to determine the current direction.

1.2 Operation of DC generator

The construction of a simple DC generator is shown in Fig. 1.1. Whenever a conductor is kept in a magnetic field, an emf is induced in the conductor. In a DC generator, magnetic field is generated by field coils and the armature conductors are rotated in the magnetic field. Thus, an emf is produced in the armature conductors. The voltage/current output waveform is shown in Fig. 1.2.

Fig. 1.1: Principle of the generator.

Fig. 1.2: Voltage across the load.

1.3 Voltage equation of a generator

Let

• P = Number of poles
• Φ = Flux/pole in weber
• Z = Number of conductors (Armature) = Number of slots × Number of conductors/slot
• N = No. of rotations in rpm; A = No. of parallel paths
• E_g = emf generated in any one parallel path in the armature

(1.1)$\mathrm{A}\mathrm{v}\mathrm{e}\mathrm{r}\mathrm{a}\mathrm{g}\mathrm{e}\mathrm{v}\mathrm{o}\mathrm{l}\mathrm{t}\mathrm{a}\mathrm{g}\mathrm{e}\mathrm{p}\mathrm{r}\mathrm{o}\mathrm{d}\mathrm{u}\mathrm{c}\mathrm{e}\mathrm{d}\mathrm{p}\mathrm{e}\mathrm{r}\mathrm{c}\mathrm{o}\mathrm{n}\mathrm{d}\mathrm{u}\mathrm{c}\mathrm{t}\mathrm{o}\mathrm{r}=\frac{\mathrm{d}\varphi }{\mathrm{d}\mathrm{t}}\mathrm{V}\mathrm{o}\mathrm{l}\mathrm{t}$

The change in flux per conductor in one revolution dϕ = ϕ × P webers

$\mathrm{T}\mathrm{h}\mathrm{e}\mathrm{f}\mathrm{l}\mathrm{u}\mathrm{x}\mathrm{c}\mathrm{h}\mathrm{a}\mathrm{n}\mathrm{g}\mathrm{e}\mathrm{s}\frac{\mathrm{N}}{60}\mathrm{r}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{s}/\mathrm{s}\mathrm{e}\mathrm{c}$

Therefore, the time taken to complete one com...

Table of contents

• Title Page
• Copyright
• Contents
• dedication
• Preface
• 1 DC Generators
• 2 DC Motors
• 3 Transformers
• 4 Induction Motors
• 5 Synchronous Generators
• 6 Synchronous Motor
• Bibliography
• Index