# Electrical Engineering II : Textbook for second year students, P. Darjanov, I. Marinova, D. Darjanova

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ONTENT
Preface 7

Chapter 1. REVIEW ON ELECTRICAL CIRCUITS FUNDAMENTALS 9

1. Electrical circuits overview 9

1.1. Basic definitions 9

1.2. Basic quantities for the electrical circuits description and analysis 10

1.3. The circuit configuration terminology 14

1.4. Fundamental laws for electrical circuits analysis application 14

1.5. Basic methods for a circuit analysis ; 15

2. Single phase AC circuit 16

2.1. Faraday’s law of electromagnetic induction 16

2.2. Sinusoidal voltage 17

2.3. Steady state response of a single element R ; L ; C circuits 18

2.4. Series R-L circuit   21

2.5. Series R-C circuit   22

2.6. Series and parallel R-L-C circuit 22

2.7. Using complex numbers for AC circuit calculations 24

3. Three phase AC industrial circuits 25

3.1. Introduction..   25

3.2. Three-phase voltage systems configurations ...26

3.3. Voltages in a 3-phase balanced industrial circuit..; 27

3.4. Basic calculations in 3-phase systems 28

3.5. Standard configurations for 3-phase industrial power supply systems.29

4. Computer-aided analyses of electrical circuits ....31

Chapter 2. MAGNETIC CIRCUITS IN ELECTRICAL ENGINEERING 33

1. Introduction to magnetic circuits 33

1.1. The magnetic field 33

1.2. Magnetic materials properties 35

: 1.3. Magnetization curves 37

1.4. Magnetic field sources ; 39

2. Magnetic circuit analysis 41

2.1. The concept of magnetic circuit .• 41

2.2. Ampere’s circuital law (ACL) 42

2.3. Magnetic resistance definition   42

2.4. The equivalent magnetic scheme 45

2.5. AC analysis of magnetic circuits     48

3. Computer-aided analyses of magnetic circuits 52
1. General information 54

2. Principle of operation of a single-phase, two windings, iron core

transformer 55

3. Transformer as an electrical circuit element 59

3.1. The transformer equivalent circuit 61

3.2. Change of the secondary voltage U2 under load 63

3.3. Open and short secondary circuit test of transformers 65

3.4. The multi-winding transformer 69

4. Three -phase transformers 69

4.1. The symmetrical three-phase transformer core configuration 70

4.2. Non-symmetrical three-phase transformer 71

4.3. Group connection of windings :...71

4.4. General discussion on power transformers construction and design ....73

4.5. Heating and cooling of transformers 77

5. Special transformers 79

5.1. Autotransformer 79

5.2. Instrument transformers 81

5.3. Welding transformer '. 89

5.4. Audio-frequency trans formers 90

5.5. Small power supply transformers 91

Chapter 4. ELECTRICAL MACHINES 95

1. Basic construction 96

2. Principle of operation 103

3. Electric motors 103

4. Electric generators 104

4.1. Types of generators 106

4.2. Energy Sources and Prime Movers   106

Chapter 5. AC MACHINES , ; Ю7

1. AC machines fundamentals 107

1.1. Rotating magnetic field 107

1.2. Induced voltage

1.3. Torque in AC machines Ill

1.4. Losses in AC machines ; 112

2. Induction machines 113

2.1. Induction motors 113

2.2. Linear motors 132
3. Synchronous machines 132

3.1. Synchronous machine construction 133

3.2. Principle of operation 135

3.3. Open and short-circuit characteristics 137

3.4. Torque-speed characteristics 138

3.5. Excitation characteristics 139

3.6. Hysteresis motors 140

3.7. Reluctance motors 141

3.8. Permanent magnet motors     141

Chapter 6. DC MACHINES 143

1. Basic construction 144

2. Principles of operation 145

3. Commutation 150

4. Compensation 151

5. Methods of excitation of the field windings 152

5.1. Separate excitation 152

5.2. Series connection 152

5.3. Shunt connection 153

5.4. Compound connection - ....154

6. Characteristics of DC machines 155

7. DC Motor speed control 156

7.1. Field-current control     156

7.2. Armature-circuit-resistance control 156

7.3.. Armature-terminal-voltage control   157.

8. Permanent magnet machines 158

9. Brushless DC motors   158

10. Stepper Motors..... : 159

11. Universal Motors 160

Chapter 7. SWITCHING AND PROTECTION OF ELECTRICAL POWER

CIRCUITS. ELECTRICAL SWITCHGEAR .161

1. Introduction 161

2. Electrical contacts and electric arc overview...-. 162

2.1. Electric contact definition •*•••* 162

2.2. Electric arc definition 165

3. The fuse as a circuit protection element 171

3.1. The fuse basic definitions 131

3.2. The fuse construction and application overview 175

4. Electromagnetic contactor as a circuit switching element 178

4.1. Principle of operation and some basic definitions 178

4.2. Motor starters : 181
5. Low-voltage automatic circuit breakers as a circuit switching

and protection element   184

5.1. Principle of operation and some basic definitions 184

5.2. Examples of some CB for industry application 187

6. High voltage circuit breakers 189

6.1. General discussion 189

6.2. Oil circuit breakers 190

6.3. Air circuit breakers 191

6.4. Vacuum circuit breakers 192

6.5. Gas insulated circuit breakers 195

Chapter 8. ELECTROMAGNETIC INTERACTIONS 198

1. General discussion    198

2. Electro-dynamic forces determination 200

2.1. DC analyses of some typical conductor configurations 200

2.2. Electro-dynamic forces in AC driven circuits 204

3. Electromagnetic force development in electromagnets 205

Chapter 9. ELECTRICAL POWER GENERATION OVERVIEW 209

1. General remarks on the energy sources and energy conversion 209

2. Review on the conventional methods of electrical power generation 211

2.1. The hydroelectric power plant principle of operation 211

2.2 - The thermal power plant principle of operation 213

2.3. The nuclear power plant principle of operation 214

3. Review on the methods of renewable electrical power generation 216

3.1. Solar radiation conversion into electrical energy 216

3.2. Wind energy conversion into electrical energy 219

3.3. More resources for renewable energy conversion into electrical

energy.... ; 220

List of some International Electrotechnical Commission (IEC) standards related to the textbook topi& ■. -223

Refer en ce 1 224
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