Page 7 - Basics of Electrical, Electronic and Communication

CONTENTS xiii

4.14.4 Power factor . . . . . . . . . . . . . . . . . . 91
4.15 Impedance in polar and rectangular forms . . . . . . . 97
4.16 Admittance . . . . . . . . . . . . . . . . . . . . . . . 98
4.17 Resonance in series RLC circuit . . . . . . . . . . . . 102
4.18 Resonance in parallel RLC circuit . . . . . . . . . . . 103
4.19 Comparison of series and parallel resonant circuits . . 105

5 Three Phase Circuits 107
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . 107
5.2 Advantages of three-phase system . . . . . . . . . . . 107
5.3 Generation of 3-phase ac voltage . . . . . . . . . . . . 108
5.4 Phase sequence . . . . . . . . . . . . . . . . . . . . . 109
5.5 Three phase connections . . . . . . . . . . . . . . . . 110
5.6 Star or Wye (Y) connection . . . . . . . . . . . . . . . 110
5.6.1 Voltage and current in a Y connected circuit . . 111
5.6.2 Power in star connected system . . . . . . . . 113
5.6.3 Neutral current in Y connected system . . . . . 114
5.7 Delta or mesh connection . . . . . . . . . . . . . . . . 118
5.7.1 Power in delta connected system . . . . . . . . 120

6 Transformers 125
6.1 Principle of operation . . . . . . . . . . . . . . . . . . 125
6.2 Concept of an ideal transformer . . . . . . . . . . . . 126
6.3 EMF equation . . . . . . . . . . . . . . . . . . . . . . 127
6.4 Voltage transformation ratio and current ratio . . . . . 129
6.5 Construction of transformer . . . . . . . . . . . . . . . 130
6.5.1 Core type transformer . . . . . . . . . . . . . 131
6.5.2 Shell type transformer . . . . . . . . . . . . . 131

7 DC machines 135
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . 135
7.2 Principle of dc Generator . . . . . . . . . . . . . . . . 136
7.3 Simple loop generator . . . . . . . . . . . . . . . . . . 136
7.4 Constructional details of dc Machine . . . . . . . . . . 138
7.5 EMF equation of a dc generator . . . . . . . . . . . . 142
7.6 Types of dc generators . . . . . . . . . . . . . . . . . 144
7.7 Separately excited dc generator . . . . . . . . . . . . . 144

xiii