Electrical Machines II : For JNTUK

Description

Cover Contents Preface Roadmap to the Syllabus Chapter 1: Transformers 1.1 Definition 1.2 Basic Principle 1.3 Types of Transformers 1.4 Construction of Single-Phase Transformer 1.4.1 Core Type 1.4.2 Shell Type 1.4.3 Spiral Core Type 1.5 Transformer Windings 1.5.1 Concentric Windings 1.6 Terminals and Leads 1.7 Bushings 1.8 Tapping 1.9 Cooling of Transformer 1.10 Transformer Oil 1.11 Conservator and Breather 1.12 Buchholz Relay 1.13 Transformer Tank 1.14 Theory of Transformer 1.15 Emf Equation of a Transformer 1.16 Step-Up and Step-Down Transformer 1.17 Transformer on No Load 1.18 Transformer on Load 1.19 Equivalent Resistance 1.20 Magnetic Leakage 1.21 Equivalent Reactance 1.22 Transformer with Resistance and Leakage Reactance 1.23 Equivalent Circuit 1.24 Open Circuit Test or No-Load Test 1.25 Short Circuit or Impedance Test 1.26 Separation of Core (or Iron) Losses in a Transformer 1.27 Total Approximate Voltage Drop of a Transformer 1.28 Exact Voltage Drop 1.29 Per Unit Resistance, Leakage Reactance and Impedance Voltage Drop 1.30 Voltage Regulation of Transformer 1.30.1 Inherent Voltage Regulation 1.30.2 Voltage Regulation Down 1.30.3 Voltage Regulation Up 1.31 Calculation for Voltage Regulation 1.31.1 Zero Voltage Regulation 1.31.2 Condition for Maximum Voltage Regulation 1.31.3 Kapp’s Regulation 1.32 Losses in a Transformer 1.32.1 Core or Iron Loss 1.32.2 Copper Loss 1.33 Efficiency of a Transformer 1.34 Condition for Maximum Effi ciency 1.34.1 Load Current at Maximum Efficiency 1.34.2 kVA Supplied at Maximum Efficiency 1.35 All-Day Efficiency 1.36 Polarity Test of a Single-Phase Transformer 1.37 Sumpner’s Test 1.38 Parallel Operation of Single-Phase Transformer 1.39 Load Sharing by Two Transformers 1.39.1 Equal Voltage Ratios 1.40 Autotransformers 1.40.1 Construction 1.40.2 Copper Saving in Autotransformer 1.40.3 Conversion of Two-winding Transformerinto Single-phase Transformer 1.40.4 Advantages of Autotransformers 1.40.5 Disadvantages of Autotransformers 1.40.6 Applications of Autotransformers 1.41 Pulse Transformer 1.41.1 Pulse Response Characteristics 1.41.2 Usage of Pulse Transformer 1.42 Welding Transformers 1.42.1 Reactors Used with Welding Transformers 1.43 Current Transformer 1.44 Potential Transformer 1.45 Tap Changing Transformers 1.46 Off-Load Tap-Changing Transformers 1.47 On-Load Tap-Changing Transformers 1.48 On-Load Tap Changer with Single Primary 1.49 Preventive Autotransformer 1.50 Booster Transformer 1.51 Inrush Phenomenon Additional Solved Problems Significant Points Short Questions and Answers Supplementary Problems Multiple-choice Questions and Answers Chapter 2: Three-phase Transformers 2.1 Advantages of Three-Phase Transformers 2.2 Principle of Operation 2.3 Construction of Three-Phase Transformers 2.3.1 Core-type Construction 2.3.2 Shell-type Construction 2.4 Three-Phase Transformer Connection 2.4.1 Star–Star (g g Connection 2.4.2 Delta–Delta (Δ/Δ) Connection 2.4.3 Star–Delta (g Δ) Connection 2.4.4 Delta–Star (Δ/g Connection 2.4.5 Delta–Zig-zag Star Connection 2.5 Open-Delta or V–V Connection 2.6 Scott Connection or T–T Connection 2.7 Three-Phase to Two-Phase Conversion 2.8 Parallel Operations of Transformers 2.9 Three-Phase to Six-Phase Conversion 2.9.1 Double-star Connection 2.9.2 Double-delta Connection 2.9.3 Six-phase Star Connection 2.9.4 Diametrical Connection 2.10 Three-Winding Transformer 2.11 Three-Phase Transformer Connections 2.12 Rating of Transformers Additional Solved Problems Significant Points Short Questions and Answers Supplementary Problems Multiple-choice Questions and Answers Chapter 3: Basic Concepts of Rotating Machines 3.1 Electromagnetic Torque 3.2 Reluctance Torque 3.3 Constructional Features of Rotating Electrical Machines 3.4 Construction of DC Machines 3.4.1 Magnetic Frame or Yoke 3.4.2 Pole Cores and Pole Shoes 3.4.3 Pole Coils 3.4.4 Armature Core 3.4.5 Armature Windings 3.4.6 Commutator 3.4.7 Brushes and Bearings 3.5 Ring Windings 3.6 Drum Windings 3.6.1 Number of Coil Sidesper Layer 3.6.2 Coil Span 3.6.3 Winding Pitch 3.6.4 Commutator Pitch 3.6.5 Numbering of Armature Conductors 3.6.6 Difference between Coil Span and Winding Pitch 3.7 Types of DC Windings 3.7.1 Simple Lap Winding 3.7.2 Wave Winding 3.8 Equalizing Connections for Lap Winding 3.9 Uses of Lap and Wave Windings 3.10 Dummy Coils 3.11 Principle of DC Generator 3.12 Operation of a Simple DC Generator with a Two-Segment Commutator 3.13 Principle of DC Motor 3.14 Construction of Synchronous Machines 3.14.1 Stator 3.14.2 Rotor 3.14.3 Classification of Synchronous MachinesBased on the Prime Mover 3.14.4 Excitation System 3.14.5 Damper Windings 3.14.6 Frequency and Synchronous Speed 3.14.7 Armature Windings 3.15 Polyphase Induction Machines 3.15.1 Squirrel-cage Rotor 3.15.2 Wound Rotor 3.16 Air Gap 3.17 Principle of Operation of Three-Phase Induction Motor 3.18 Synchronous Speed and Slip in Induction Motor 3.18.1 Synchronous Speed 3.18.2 Slip in Induction Motor 3.19 Frequency of Rotor Currents 3.20 Speed of the Rotor MMF 3.21 Electrical and Mechanical Degrees 3.22 Pitch Factor 3.23 Distribution Factor 3.24 Winding Factor 3.25 Flux Per Pole 3.26 Generated EMF in Full-Pitched Coil 3.27 EMF Generated in AC Machines 3.27.1 Synchronous Machines 3.27.2 Induction Machines 3.27.3 A General Expression for the emf of Synchronous Generator 3.28 EMF Generated in DC Generator 3.29 Concept of Rotating Magnetic Field 3.29.1 Case 1: ξt = ρ = 0° 3.29.2 Case 2: ξt = ρ = 60° 3.29.3 Case 3: ξt = ρ = 120° 3.29.4 Case 4: ξt = ρ = 180° Additional Solved Problems Significant Points Short Questions and Answers Supplementary Problems Multiple-choice Questions and Answers Chapter 4: Polyphase Induction Motors 4.1 Rotor Current 4.2 Rotor Power 4.3 Expression for Torque 4.4 Starting Torque 4.4.1 Starting Torque of a Squirrel-cage Motor 4.4.2 Starting Torque of Slip-ring Motor 4.5 Effect of Change in Supply Voltage on Starting Torque 4.6 Effect of Change in Supply Voltage on Torque and Slip 4.7 Condition for Maximum Torque 4.8 Torque-Slip and Torque-Speed Characteristics 4.9 Relation between Full-Load Torque and Maximum Torque 4.10 Relation between Starting Load Torque and Maximum Torque 4.11 Condition for the Starting Torque to be Equal to the Maximum Torque 4.12 Effect of Variation of Rotor Resistance and Rotor Reactance on Maximum Torque, Efficiency and Power Factor of an Induction Motor 4.12.1 Effect of Rotor Resistance on Maximum Torque 4.12.2 Effect of R2 and X2 on the Power Factorof an Induction Motor 4.12.3 Effect of R2 and X2 on the Efficiency of an Induction Motor 4.13 Effect of Change in Supply Voltage on Torque and Speed 4.14 Effect of Change in Supply Frequency on Torque and Speed 4.15 Losses 4.16 Power Stages 4.17 Efficiency 4.18 Synchronous Watt 4.19 Measurement of Slip 4.19.1 Electromechanical Counter 4.19.2 Mechanical Differential Counter 4.19.3 Stroboscopic Method 4.20 Equivalent Circuit 4.20.1 Stator Equivalent Circuit 4.20.2 Rotor Equivalent Circuit 4.21 Thevenin’s Equivalent Circuit of an Induction Motor 4.22 Starting of Induction Motors 4.23 Starting of Squirrel-Cage Motors 4.23.1 Direct-on-line starting of induction motors 4.23.2 Stator Resistor (or Reactor) Starting 4.23.3 Autotransformer Starting 4.23.4 Star-delta Starter 4.24 Starting of Slip-Ring Induction Motors 4.25 No-Load Test or Open-Circuit Test 4.26 Blocked-Rotor or Short-Circuit Test 4.27 Direct Testing of Induction Motors 4.28 Circle Diagram 4.29 Speed Control of Induction Motor 4.29.1 Speed Control from Rotor Side 4.29.2 Speed Control of Induction Motors from Stator Side 4.30 Comparison between Wound-Rotor and Cage-Rotor Induction Motors 4.31 Crawling 4.32 Magnetic Locking (Cogging) 4.33 Deep-Cage Rotors 4.34 Double-Cage Rotors 4.35 Applications 4.36 Comparison between Synchronous and Induction Motors 4.37 Factors Governing the Performance of Induction Motors 4.38 Effects of Operating Conditions 4.39 Ratings of Induction Motor 4.40 Common Faults in Three-Phase Induction Motors 4.41 Most Probable Reasons for Which Three-Phase Induction Motors Fail to Start 4.42 Most Probable Reasons for Which Three-Phase Induction Motors Fail to Carry Load 4.43 Schrage Motor 4.44 Power Factor Compensation 4.45 Linear Induction Motor 4.46 Induction Generator 4.47 Electrical Braking of Polyphase Induction Motors 4.47.1 Regenerative Braking 4.47.2 Plugging or Counter-current Braking 4.47.3 Dynamic Braking 4.48 Synchronous-Induction Motor Additional Solved Problems Significant Points Short Questions and Answers Supplementary Problems Multiple-choice Questions and Answers Solved Question Papers Index