i UNIT - I SYLLABUS osmania university UNIT - II CHAPTER - 1 : PRINCIPLES OF ELECTRO-MECHANICAL ENERGY CONVERSION Energy in Magnetic System, Field Energy and Mechanical Force, Direction of Mechanical Force Developed, Flow of Energy in Electro-Mechanical Devices, Singly Excited and Multiply Excited Systems, Basic Concepts of Magnetically Induced EMF and Force. CHAPTER - 2 : DC MACHINES Brief Description of Constructional Features, Armature Windings, Simple Lap and Wave Windings, Brush Position, Classification of DC Machines. CHAPTER - 3 : DC GENERATORS UNIT - III Generated EMF, Methods of Excitation, Armature Reaction, Theory of Commutation, Types of Generators and their Characteristics, Series and Parallel Operation. CHAPTER - 4 : DC MOTORS UNIT - IV Generation of Electromagnetic Torque, Types of Motors and their Characteristics, Application of Motors, Starting and Speed Control of DC Motors, Testing of DC Motors, Losses and Efficiency, Temperature Rise and Swinburne s Test, Hopkinson s Test, Field s Test for Series Motors, Retardation Test, Separation of Losses. CHAPTER - 5 : SINGLE-PHASE TRANSFORMERS Constructional Features, Principle of Operation, Ideal Transformer, Transformer on No- Load and On-Load, Vector Diagrams, Equivalent Circuit, Losses, Testing, Polarity Test, O.C and S.C Tests, Sumpner s Test, Regulation and Efficiency, All Day Efficiency, Separation of Losses, Excitation Phenomena of Transformers.
ii UNIT - V CHAPTER - 6 : THREE-PHASE TRANSFORMERS Three-Phase Transformers Connections Y-Y, D-D, D-Y, Y-D, V-V and Scott Connections. CHAPTER - 7 : STEPPER MOTORS Types of Stepper Motors, Parameters, Characteristics, Drive Circuits and Applications.
iii electrical machinery i FOR b.e. (o.u) Ii year ii semester (ELECTRICAL AND ELECTRONICS ENGINEERING) CONTENTS UNIT - I [CH. H. - 1] ] [PRINCIPLES OF ELECTRO-MECHANICAL ENERGY CONVERSION]... 1.1-1.74 1.1 INTRODUCTION... 1.2 1.2 PRINCIPLES OF ELECTRO-MECHANICAL ENERGY CONVERSION... 1.3 1.3 ENERGY IN MAGNETIC SYSTEM... 1.5 1.3.1 i-λ Relationship... 1.7 1.3.2 Co-Energy and Field Energy... 1.8 1.3.3 Energy Density... 1.11 1.4 MECHANICAL FORCE EXERTED... 1.12 1.4.1 Current Excited System... 1.14 1.4.2 Voltage Excited System... 1.15 1.4.3 Linear Case... 1.15 1.4.4 Non Linear Case... 1.16 1.4.5 Direction of Mechanical Force Developed... 1.16 1.4.5.1 Mechanical Energy... 1.17 1.5 ENERGY FLOW IN ELECTRO-MECHANICAL ENERGY CONVERSION DEVICE... 1.18 1.6 TYPES OF MAGNETIC SYSTEMS... 1.19 1.6.1 Singly Excited System... 1.20
iv 1.6.2 Multiply Excited System... 1.26 1.6.2.1 Flux Linkages as Independent Variables... 1.27 1.6.2.2 Currents as Independent Variables... 1.29 1.7 BASIC CONCEPTS OF MAGNETICALL GNETICALLY INDUCED EMF AND FORCE... 1.29 1.7.1 Electro Magnetic Induction... 1.29 1.7.2 Faraday araday s Laws of Electro Magnetic Induction... 1.31 1.7.3 Lenz s Law and Fleming s Right and Left Hand Rule... 1.32 1.7.3.1 Lenz s Law... 1.32 1.7.3.2 Fleming s Right Hand Rule... 1.33 1.7.3.3 Fleming s Left Hand Rule... 1.34 1.7.3.4 Cork Screw Rule... 1.34 1.8 ENERGY IN ELECTRIC FIELD... 1.35 1.8.1 Electric Field Energy... 1.35 1.8.2 Energy Conversion... 1.37 1.9 SOLVED PROBLEMS... 1.39 Short Questions and Answers... 1.67-1.71 Expected University Questions with Answers... 1.72-1.73 UNIT - II [CH. - 2] ] [DC MACHINES]... 2.1-2.58 2.1 INTRODUCTION... 2.2 2.2 CLASSIFICATION OF ELECTRICAL MACHINES... 2.2 2.3 GENERAL CONSTRUCTION OF ROTATING TING MACHINE... 2.3 2.4 CLASSIFICATION OF DC MACHINES CHINES... 2.4 2.4.1 Basic Working Principle of DC Machine as a Generator... 2.4 2.4.2 Basic Working Principle of DC Machine as a Motor... 2.6
v 2.5 CONSTRUCTIONAL FEATURES OF DC MACHINES CHINES... 2.6 2.5.1 Stator... 2.7 2.5.1.1 Yoke (or) Magnetic Frame rame... 2.7 2.5.1.2 Field Poles oles... 2.8 2.5.1.3 Field Windings... 2.9 2.5.1.4 Interpoles... 2.10 2.5.2 Rotor... 2.10 2.5.2.1 Armature Core... 2.10 2.5.2.2 Armature Windings... 2.12 2.5.2.3 Commutator... 2.12 2.5.2.4 Brushes... 2.13 2.5.2.5 Bearings... 2.13 2.5.2.6 Armature Shaft... 2.14 2.6 ARMATURE WINDINGS... 2.14 2.6.1 Terminology used in Armature Windings... 2.14 2.7 CLASSIFICATION OF ARMATURE WINDINGS... 2.19 2.7.1 Simplex Lap Windings... 2.19 2.7.2 Simplex Wave Windings... 2.21 2.7.3 Armature Parallel Paths... 2.23 2.7.4 Comparison between Lap and Wave Windings... 2.24 2.7.5 Solved Problems... 2.24 2.8 EMF EQUATION OF DC MACHINES... 2.29 2.8.1 Solved Problems... 2.31 2.9 CIRCUIT MODEL OF DC MACHINES... 2.36 2.10 TYPES OF DC MACHINES... 2.39 2.10.1 Separately-Excited DC Machine... 2.39
vi 2.10.2 Self Excited DC Machine... 2.40 2.10.2.1 Series Excited DC Machine... 2.40 2.10.2.2 Shunt-Excited DC Machine... 2.41 2.10.2.3 Compound-Excited DC Machine... 2.41 2.11 LOSSES IN DC MACHINES... 2.43 2.11.1 Electrical (or) Copper Losses (or) Winding Losses... 2.43 2.11.2 Magnetic Losses (or) Core Losses (or) Iron Losses... 2.44 2.11.3 Brush Losses... 2.44 2.11.4 Mechanical Losses... 2.44 2.11.5 Stray-Load Losses... 2.44 2.12 POWER-FLOW DIAGRAM... 2.45 2.13 EFFICIENCY OF A DC MACHINE... 2.46 2.14 SPEED OF A DC MACHINE... 2.47 2.14.1 Speed Regulation... 2.48 Short Questions and Answers... 2.49-2.56 Expected University Questions with Answers... 2.57 UNIT - II [CH. - 3] ] [DC GENERATORS]... 2.59-2.154 3.1 DC GENERATOR OR... 2.60 3.2 PRINCIPLE OF OPERATION OF A DC GENERATOR OR... 2.60 3.3 SIMPLE LOOP GENERATOR OR... 2.61 3.4 GENERATED EMF EQUATION OF A DC GENERATOR OR... 2.64 3.4.1 Solved Problems... 2.66 3.4.2 Factors Affecting the Induced EMF... 2.72 3.5 ARMATURE REACTION... 2.73 3.5.1 Solved Problems... 2.78 3.5.2 Effects of Armature Reaction... 2.80 3.5.3 Reduction of Effects of Armature Reaction... 2.80
vii 3.6 THEORY OF COMMUTATION TION... 2.80 3.6.1 Methods of Improving Commutation... 2.84 3.6.1.1 Resistance Commutation... 2.84 3.6.1.2 Voltage Commutation... 2.84 3.6.1.3 Compensating Windings... 2.86 3.6.2 Solved Problem... 2.86 3.7 METHODS OF EXCIT CITATION TION... 2.88 3.7.1 Separately-Excited Generators... 2.88 3.7.2 Self-Excited DC Generators... 2.89 3.7.2.1 Series DC Generator... 2.89 3.7.2.2 Shunt DC Generator... 2.91 3.7.2.3 Compound DC Generator... 2.92 3.7.3 Solved Problems... 2.94 3.8 CHARACTERISTICS CTERISTICS OF DIFFERENT TYPES OF GENERATORS... 2.101 3.8.1 Characteristics of Separately-Excited DC Generator... 2.101 3.8.2 Characteristics of DC Shunt Generator... 2.104 3.8.3 Characteristics of DC Series Generator... 2.105 3.8.4 Characteristics of Compound DC Generators... 2.106 3.8.5 Solved Problems... 2.107 3.9 APPLICATIONS OF DC GENERATOR OR... 2.114 3.10 SERIES AND PARALLEL OPERATION OF GENERATOR OR... 2.114 3.10.1 Series Operation of Generator... 2.115 3.10.1.1 Series Operation of Series Generators... 2.115 3.10.1.2 Series Operation of Shunt Generator... 2.115 3.10.2 Parallel Operation of Generator... 2.116 3.10.2.1 Parallel Operation of Shunt Generators... 2.116 3.10.2.2 Parallel Operation of Compound Generators... 2.118
viii 3.10.2.3 Parallel Operation of Series Generators... 2.120 3.10.2.4 Necessity of Parallel Operation of Generators... 2.121 3.10.2.5 Requirements of Parallel Operation of Generators... 2.122 3.10.2.6 Solved Problems... 2.122 ` Short Questions and Answers... 2.145-2.151 Expected University Questions with Answers... 2.152-2.153 UNIT - III [CH. H. - 4] ] [DC MOTORS]... 3.1-3.144 4.1 INTRODUCTION... 3.2 4.2 MOTOR OR PRINCIPLE AND ITS OPERATION... 3.2 4.2.1 Motor Principle... 3.2 4.2.2 Operation of DC Motor... 3.3 4.2.3 Solved Problems... 3.4 4.3 BACK (OR) COUNTER EMF... 3.5 4.3.1 Value of Back EMF... 3.6 4.3.2 Importance of Back EMF... 3.7 4.3.3 Voltage Equation of DC Motor... 3.8 4.3.4 Power Equation of DC Motor... 3.8 4.3.5 Solved Problems... 3.9 4.3.6 Equivalent Circuit of a DC Motor Armature... 3.14 4.4 TYPES OF TORQUE IN THE MOTOR OR... 3.15 4.4.1 Torque Equation of a DC Motor... 3.15 4.4.2 Speed and Torque Equation... 3.17 4.4.3 Solved Problems... 3.19 4.5 TYPES OF DC MOTORS ORS... 3.30 4.5.1 Separately-Excited DC Motor... 3.31 4.5.2 Self-Excited DC Motor... 3.31 4.5.3 Solved Problems... 3.35
ix 4.6 ARMATURE REACTION IN A DC MOTOR OR AND INTERPOLES... 3.41 4.7 CHARACTERISTICS CTERISTICS OF DC MOTOR OR... 3.42 4.7.1 Characteristics of DC Shunt Motor... 3.42 4.7.2 Characteristics of DC Series Motor... 3.44 4.7.3 Characteristics of DC Compound Motors... 3.46 4.8 APPLICATIONS OF DC MOTORS ORS... 3.47 4.9 STAR ARTING OF D.C MOTORS ORS... 3.48 4.9.1 Necessity of a Starter... 3.48 4.9.2 Types of DC Motor Starters... 3.49 4.9.2.1 Two wo-p -Point Starter... 3.50 4.9.2.2 Three-P -Point Starter... 3.51 4.9.2.3 Four our-p -Point Starter... 3.53 4.9.3 Solved Problems... 3.54 4.10 SPEED CONTROL OF DC MOTORS ORS... 3.58 4.10.1 Armature Resistance Control (Rheostatic Control)... 3.58 4.10.2 Variation of Field Flux φ (Field Flux Control)... 3.60 4.10.3 Armature Voltage Control... 3.62 4.10.4 Solved Problems... 3.64 4.11 TESTING OF DC MOTORS ORS... 3.84 4.11.1 Temperature Rise and Swinburne s Test est... 3.84 4.11.1.1 Solved Problems... 3.87 4.11.2 Hopkinson s Test (or) Regenerative Test (or) Back-to -to-back -Back Test (or) Heat-R -Run Test... 3.105 4.11.2.1 Solved Problems... 3.109 4.11.3 Brake Test est... 3.115 4.11.3.1 Solved Problems... 3.117
x 4.11.4 Retardation Test (or) Running Down Test est... 3.125 4.11.4.1 Solved Problem... 3.127 4.11.5 Field s Test for Series Motors... 3.129 4.11.6 Separation of Losses... 3.131 Short Questions and Answers... 3.135-3.142 Expected University Questions with Answers... 3.143-3.144 UNIT - IV [CH. H. - 5] ] [SINGLE-PHASE TRANSFORMERS]... 4.1-4.118 5.1 INTRODUCTION... 4.2 5.2 WORKING PRINCIPLE OF TRANSFORMER... 4.2 5.3 CLASSIFICATION OF TRANSFORMER... 4.3 5.3.1 Classification According to Transformer Use... 4.3 5.3.2 Classification According to Core Construction... 4.4 5.3.3 Classification According to Transformer Ratio atio... 4.4 5.3.4 Classification According to Transformer Insulating Medium... 4.5 5.3.5 Classification According to Input Supply... 4.5 5.3.6 Classification According to Cooling Method... 4.5 5.4 CONSTRUCTION OF SINGLE-PHASE TRANSFORMERS... 4.6 5.4.1 Detailed Construction of Transformer... 4.9 5.5 THEORY Y OF OPERATION... 4.11 5.5.1 EMF Equation of a Transformer... 4.12 5.5.1.1 Solved Problem... 4.15 5.5.2 Transformer (or) Turns Ratio atio... 4.16 5.5.3 KVA Rating of a Transformer... 4.18 5.5.4 Solved Problems... 4.19 5.6 IDEAL TRANSFORMER... 4.28 5.6.1 Solved Problems... 4.31
xi 5.7 TRANSFORMER ON NO-LO -LOAD AD AND ON LOAD AD... 4.33 5.7.1 Transformer on No-L -Load oad... 4.33 5.7.1.1 Phasor (or) Vector Diagram at No-L -Load oad... 4.33 5.7.1.2 Solved Problems... 4.34 5.7.1.3 No-Load Equivalent Circuit... 4.39 5.7.2 Transformer on On-L On-Load oad... 4.40 5.7.2.1 Operation of Transformer On-Load... 4.41 5.7.2.2 Phasor (or) Vector Diagram for a Loaded Transformer (Neglecting Voltage Drop in the Windings and Ampere Turn Balance)... 4.43 5.7.2.3 Solved Problems... 4.44 5.8 EQUIVALENT CIRCUIT OF TRANSFORMER... 4.47 5.8.1 Solved Problem... 4.51 5.9.9 ADVANT ANTAGES OF SINGLE-PHASE TRANSFORMER... 4.54 5.10 TESTING OF A SINGLE-PHASE TRANSFORMER... 4.54 5.11 POLARITY TEST ON TRANSFORMER... 4.55 5.12 OC AND SC TESTS ON TRANSFORMER... 4.55 5.12.1 Open-Circuit Test est... 4.55 5.12.2 Short-Circuit Test est... 4.57 5.12.3 Solved Problems... 4.58 5.13 SUMPNER S TEST (OR) BACK CK-TO-BA -BACK CK TEST ON TRANSFORMER... 4.67 5.13.1 Advantages of Sumpner s Test... 4.69 5.14 VOLTAGE REGULATION OF A TRANSFORMER... 4.69 5.14.1 Mathematical Relation for Regulation... 4.69 5.14.1.1 Solved Problems... 4.73 5.14.2 Condition for Zero-Voltage oltage Regulation... 4.76 5.14.3 Condition for Maximum-Voltage Regulation... 4.76
xii 5.15 EFFICIENCY OF A TRANSFORMER... 4.77 5.15.1 Condition for Maximum Efficiency of a Transformer... 4.78 5.15.2 Current and KVA Rating at Maximum Efficiency... 4.79 5.15.3 Solved Problems... 4.80 5.16 ALL-DA -DAY EFFICIENCY OR ENERGY EFFICIENCY... 4.93 5.16.1 Solved Problems... 4.93 5.17 TRANSFORMER LOSSES... 4.98 5.17.1 Copper-Losses... 4.98 5.17.2 Core-Losses (or) Iron... 4.99 5.17.2.1 Hysteresis Loss... 4.99 5.17.2.2 Eddy-Current Loss... 4.100 5.18 SEPARA ARATION OF LOSSES... 4.101 5.18.1 Solved Problems... 4.102 5.19 EXCIT CITATION TION PHENOMENA OF TRANSFORMERS... 4.104 5.19.1 Current Inrush Phenomenon (Switching Transients)... 4.106 5.20 APPLICATIONS OF TRANSFORMER... 4.107 Short Questions and Answers... 4.109-4.115 Expected University Questions with Answers... 4.116-4.118 UNIT - V [CH. - 6] ] [THREE-PHASE TRANSFORMERS]... 5.1-5.54 6.1 INTRODUCTION... 5.2 6.2 BASIC COMPONENTS OF THREE-PHASE TRANSFORMER... 5.2 6.3 CONSTRUCTION OF THREE-PHASE TRANSFORMER... 5.3 6.3.1 Advantages of a Three-Phase Single Unit Transformer... 5.5 6.3.2 Disadvantages of a Three-Phase Single Unit Transformer... 5.6 6.3.3 Advantages of a Transformer Bank of Three Single-Phase Transformers... 5.6
xiii 6.4 THREE-PHASE TRANSFORMER GROUPS... 5.6 6.5 TYPES OF THREE-PHASE TRANSFORMERS... 5.8 6.5.1 Factors Affecting the Choice of Connections... 5.8 6.6 DELTA-DEL -DELTA (Δ-Δ) ) CONNECTION... 5.8 6.6.1 Advantages of Δ-Δ Transformation... 5.10 6.6.2 Disadvantages of Δ-Δ Transformation... 5.10 6.7 STAR AR-ST STAR (Y-Y) Y) CONNECTION... 5.10 6.7.1 Advantages of Star-Star Connection... 5.11 6.7.2 Disadvantages of Star-Star Connection... 5.11 6.8 STAR AR-DEL -DELTA A (Y-Δ) ) CONNECTION... 5.12 6.8.1 Advantages and Disadvantages of Star-Delta Connection... 5.13 6.8.2 Solved Problems... 5.14 6.9 DELTA-ST STAR AR (Δ-Y) CONNECTION... 5.16 6.9.1 Advantages and Disadvantages of Delta-Star Connection... 5.18 6.10 OPEN-DELTA (OR) V-V V CONNECTION... 5.18 6.10.1 Applications of Open-Delta System... 5.22 6.10.2 Solved Problems... 5.22 6.11 SCOTT TT (THREE-PHASE TO O TWO-PHASE) CONNECTION... 5.26 6.11.1 Position of Neutral Point N... 5.30 6.11.2 Relationship between Input and Output Currents... 5.31 6.11.3 Applications of Scott Connection... 5.35 6.11.4 Solved Problems... 5.36 6.12 SOLVED PROBLEMS... 5.45 Short Questions and Answers... 5.49-5.52 Expected University Questions with Answers... 5.53-5.54
xiv UNIT - V [CH. H. - 7] ] [STEPPER MOTORS]... 5.55-5.106 7.1 INTRODUCTION... 5.56 7.2 OPERATING PRINCIPLE OF STEPPER MOTORS ORS... 5.56 7.3 PARAMETERS OF STEPPER MOTOR OR... 5.58 7.3.1 Step Angle... 5.58 7.3.2 Resolution (or) Step Number... 5.59 7.3.3 Slewing... 5.59 7.4 TYPES OF STEPPER MOTOR OR... 5.60 7.5 VARIABLE RELUCT UCTANCE STEPPER MOTOR OR (VRSM)... 5.62 7.5.1 Advantages of Variable Reluctance Stepper Motor... 5.71 7.5.2 Disadvantages of Variable Reluctance Motor... 5.71 7.6 PERMANENT MAGNET STEPPER MOTOR OR (PMSM)... 5.72 7.6.1 Advantages of Permanent Magnet Stepper Motor... 5.79 7.6.2 Disadvantages of Permanent Magnet Stepper Motor... 5.79 7.7 HYBRID STEPPER MOTOR OR... 5.79 7.7.1 Advantages of Hybrid Stepper Motors... 5.81 7.7.2 Disadvantages of Hybrid Stepper Motors... 5.81 7.8 CHARACTERISTICS CTERISTICS OF STEPPER MOTOR OR... 5.81 7.8.1 Static Characteristics... 5.82 7.8.2 Dynamic Characteristics... 5.84 7.9 DRIVE CIRCUIT... 5.86 7.9.1 Simple Power Drive Circuit... 5.87 7.9.2 Dual Voltage Drive... 5.88 7.9.3 Chopper Drive... 5.90
xv 7.9.4 Bipolar Drives for Stepper Motors... 5.92 7.9.4.1 Comparison between Bipolar and Unipolar Drives... 5.97 7.9.4.2 Advantages of Bipolar Drive... 5.98 7.9.4.3 Disadvantages of Bipolar Drive... 5.98 7.10 ADVANT ANTAGES OF STEPPER MOTOR OR... 5.98 7.11 DISADVANT ANTAGES OF STEPPER MOTOR OR... 5.99 7.12 APPLICATIONS OF STEPPER MOTOR OR... 5.99 Short Questions and Answers... 5.101-5.105 Expected University Questions with Answers... 5.106 LATEST UNIVERSITY QUESTION PAPER WITH ANSWERS [April/May - 2013] [New] [Main]... QP.1 - QP.14 [January - 2013] [New] [Supplementary]... QP.15 - QP.28
xvi STUDENT NOTES