Electrical machines

Contents
Preface
Acknowledgements
1. Electro Magnetic Circuits
	Introduction
	1.1 Magnetic Field and its Significance
	1.2 Magnetic Circuit and its Analysis
	1.3 Important Terms
	1.4 Comparison between Magnetic and Electric Circuits
	1.5 Ampere-turns Calculations
	1.6 Series Magnetic Circuits
	1.7 Parallel Magnetic Circuits
	1.8 Leakage Flux
	1.9 Magnetisation or B-H Curve
	1.10 Magnetic Hysteresis
	1.11 Hysteresis Loss
	1.12 Importance of Hysteresis Loop
	Section Practice Problems
	1.13 Electro Magnetic Induction
	1.14 Faraday’s Laws of Electromagnetic Induction
	1.15 Direction of Induced emf
	1.16 Induced emf
	1.17 Dynamically Induced emf
	1.18 Statically Induced emf
	1.19 Self Inductance
	1.20 Mutual Inductance
	1.21 Co-efficient of Coupling
	1.22 Inductances in Series and Parallel
	1.23 Energy Stored in a Magnetic Field
	1.24 AC Excitation in Magnetic Circuits
	1.25 Eddy Current Loss
	Section Practice Problems
	1.26 Electro-mechanical Energy Conversion Devices
	1.27 Torque Development by the Alignment of Two Fields
		1.27.1 Soft Iron Piece Placed in the Magnetic Field
		1.27.2 Permanent Magnet Placed in the Magnetic Field
		1.27.3 Electromagnet Placed in the Magnetic Field
	1.28 Production of Torque
		1.28.1 In Case of Permanent Magnet
		1.28.2 In Case of Electromagnet
	1.29 Production of Unidirectional Torque
		1.29.1 By Rotating the Main Magnets
		1.29.2 By Changing the Direction of Flow of Current in the Conductors of Electromagnet
	1.30 emf Induced in a Rotating Coil Placed in a Magnetic Field
	1.31 Elementary Concept of Electrical Machines
		1.31.1 Operation of Machine as a Generator (Conversion of Mechanical Energy into Electric Energy)
		1.31.2 Operation of Machine as a Motor
	Section Practice Problems
	Review Questions
	Multiple Choice Questions
2. Single-Phase Transformers
	Introduction
	2.1 Transformer
	2.2 Working Principle of a Transformer
	2.3 Construction of Transformer
		2.3.1 Core Material
		2.3.2 Core Construction
		2.3.3 Transformer Winding
		2.3.4 Insulation
		2.3.5 Bushings
		2.3.6 Transformer Tank
	2.4 Simple Construction of Single-phase Small Rating (SAY 2 kVA) Transformers
	2.5 An Ideal Transformer
	2.6 Transformer on DC
	2.7 emf Equation
	Section Practice Problems
	2.8 Transformer on No-load
	2.9 Effect of Magnetisation on No-load (Exciting) Current
	2.10 Inrush of Magnetising Current
	Section Practice Problems
	2.11 Transformer on Load
	2.12 Phasor Diagram of a Loaded Transformer
	2.13 Transformer with Winding Resistance
	2.14 Mutual and Leakage Fluxes
	2.15 Equivalent Reactance
	Section Practice Problems
	2.16 Actual Transformer
	2.17 Simplified Equivalent Circuit
	2.18 Short Circuited Secondary of Transformer
	2.19 Expression for No-load Secondary Voltage
	2.20 Voltage Regulation
	2.21 Approximate Expression for Voltage Regulation
	2.22 Kapp Regulation Diagram
	Section Practice Problems
	2.23 Losses in a Transformer
	2.24 Effects of Voltage and Frequency Variations on Iron Losses
	2.25 Efficiency of a Transformer
	2.26 Condition for Maximum Efficiency
	2.27 Efficiency vs Load
	2.28 Efficiency vs Power Factor
	2.29 All-day Efficiency
	Section Practice Problems
	2.30 Transformer Tests
	2.31 Polarity Test
	2.32 Voltage Ratio Test
	2.33 Open-circuit or No-load Test
	2.34 Separation of Hysteresis and Eddy Current Losses
	2.35 Short Circuit Test
	2.36 Back-to-back Test
	Section Practice Problems
	2.37 Classification of Transformers
	2.38 Parallel Operation of Transformers
	2.39 Necessity of Parallel Operation
	2.40 Conditions for Parallel Operation of One-phase Transformers
	2.41 Load Sharing between Two Transformers Connected in Parallel
	Section Practice Problems
	2.42 Auto-transformer
	2.43 Auto-transformer vs Potential Divider
	2.44 Saving of Copper in an Auto-transformer
	2.45 Advantages of Auto-transformer over Two-winding Transformer
	2.46 Disadvantages of Auto-transformers
	2.47 Phasor Diagram of an Auto-transformer
	2.48 Equivalent Circuit of an Auto-transformer
	2.49 Simplified Equivalent Circuit of an Auto-transformer
	2.50 Conversion of a Two-winding Transformer to an Auto-transformer
	2.51 Comparison of Characteristics of Auto-transformers and Two-winding Transformers
	2.52 Applications of Auto-transformers
	Section Practice Problems
	Review Questions
	Multiple Choice Questions
3. Three-Phase Transformers
	Introduction
	3.1 Merits of Three-phase Transformer over Bank of Three Single-phase Transformers
	3.2 Construction of Three-phase Transformers
	3.3 Determination of Relative Primary and Secondary Windings in Case of Three-phase Transformer
	3.4 Polarity of Transformer Windings
	3.5 Phasor Representation of Alternating Quantities in Three-phase Transformer Connections
	3.6 Three-phase Transformer Connections
	3.7 Selection of Transformer Connections
		3.7.1 Star-Star (Yy0 or Yy6) Connections
		3.7.2 Delta-Delta (Dd0 or Dd6) Connections
		3.7.3 Star-Delta (Yd1 or Yd11) Connections
		3.7.4 Delta-Star (Dy1 or Dy11) Connections
		3.7.5 Delta-Zigzag Connections
	Section Practice Problems
	3.8 Parallel Operation of Three-phase Transformers
	3.9 Necessity of Parallel Operation of Three-phase Transformers
	3.10 Conditions for Parallel Operation of Three-phase Transformers
	3.11 Load Sharing between Three-phase Transformers Connected in Parallel
	3.12 Three Winding Transformers (Tertiary Winding)
		3.12.1 Stabilisation Provided by Tertiary Winding in Star-Star Transformer
	3.13 Tap-changers on Transformers
	3.14 Types of Tap-changers
		3.14.1 No-load (or Off-load) Tap-changer
		3.14.2 On-load Tap-changer
	Section Practice Problems
	3.15 Transformation of Three-phase Power with Two Single-phase Transformers
	3.16 Open-Delta or V-V Connections
	3.17 Comparison of Delta and Open Delta Connections
	3.18 T-T Connections or Scott Connections
	3.19 Conversion of Three-phase to Two-phase and vice-versa
	3.20 Difference between Power and Distribution Transformers
	3.21 Cooling of Transformers
	3.22 Methods of Transformer Cooling
	3.23 Power Transformer and its Auxiliaries
	3.24 Maintenance Schedule of a Transformer
	3.25 Trouble Shooting of a Transformer
	Section Practice Problems
	Review Questions
	Multiple Choice Questions
4. DC Generator
	Introduction
	4.1 DC Generator
	4.2 Main Constructional Features
	4.3 Simple Loop Generator and Function of Commutator
	4.4 Connections of Armature Coils with Commutator Segments and Location of Brushes
	4.5 Armature Winding
	4.6 Types of Armature Winding
	4.7 Drum Winding
	4.8 Lap Winding
	4.9 Numbering of Coils and Commutator Segments in Developed Winding Diagram
	4.10 Characteristics of a Simplex Lap Winding
	4.11 Characteristics of a Multiplex Lap Winding
	4.12 Equalising Connections and their Necessity
	4.13 Simplex Wave Winding
	4.14 Dummy Coils
	4.15 Applications of Lap and Wave Windings
	Section Practice Problems
	4.16 emf Equation
	4.17 Torque Equation
	4.18 Armature Reaction
	4.19 Calculations for Armature Ampere-turns
	4.20 Commutation
	4.21 Cause of Delay in the Reversal of Current in the Coil going through Commutation and its Effect
	4.22 Magnitude of Reactance Voltage
	4.23 Good Commutation and Poor Commutation
	4.24 Interpoles and their Necessity
	4.25 Compensating Winding and its Necessity
	4.26 Methods of Improving Commutation
	Section Practice Problems
	4.27 Types of DC Generators
	4.28 Separately-excited DC Generators
	4.29 Self-excited DC Generators
	4.30 Voltage Regulation of a DC Shunt Generator
	4.31 Characteristics of DC Generators
	4.32 No-load Characteristics of DC Generators or Magnetisation Curve of DC Generator
	4.33 Voltage Build-up in Shunt Generators
	4.34 Critical Field Resistance of a DC Shunt Generator
	4.35 Load Characteristics of Shunt Generator
	4.36 Load Characteristics of Series Generators
	4.37 Load Characteristics of Compound Generator
	4.38 Causes of Failure to Build-up Voltage in a Generator
	4.39 Applications of DC Generators
	4.40 Losses in a DC Generator
	4.41 Constant and Variable Losses
	4.42 Stray Losses
	4.43 Power Flow Diagram
	4.44 Efficiency of a DC Generator
	4.45 Condition for Maximum Efficiency
	Section Practice Problems
	Review Questions
	Multiple Choice Questions
5. DC Motors
	Introduction
	5.1 DC Motor
	5.2 Working Principle of DC Motors
	5.3 Back emf
	5.4 Electro-magnetic Torque Developed in DC Motor
	5.5 Shaft Torque
	5.6 Comparison of Generator and Motor Action
	5.7 Types of DC Motors
	5.8 Characteristics of DC Motors
	5.9 Characteristics of Shunt Motors
	5.10 Characteristics of Series Motors
	5.11 Characteristics of Compound Motors
	5.12 Applications and Selection of DC Motors
		5.12.1 Applications of DC Motors
		5.12.2 Selection of DC Motors
	5.13 Starting of DC Motors
	5.14 Necessity of Starter for a DC Motor
	5.15 Starters for DC Shunt and Compound Wound Motors
	5.16 Three-point Shunt Motor Starter
	5.17 Four-point Starter
	5.18 Calculation of Step Resistances Used in Shunt Motor Starter
	5.19 Series Motor Starter
	Section Practice Problems
	5.20 Speed Control of DC Motors
	5.21 Speed Control of Shunt Motors
		5.21.1 Field Control Method
		5.21.2 Armature Control Method
	5.22 Speed Control of Separately Excited Motors
	5.23 Speed Regulation
	5.24 Speed Control of DC Series Motors
		5.24.1 Armature Control Method
		5.24.2 Field Control Method
		5.24.3 Voltage Control Method
	5.25 Electric Braking
	5.26 Types of Electric Braking
		5.26.1 Plugging
		5.26.2 Rheostatic Braking
		5.26.3 Regenerative Braking
	Section Practice Problems
	5.27 Losses in a DC Machine
	5.28 Constant and Variable Losses
	5.29 Stray Losses
	5.30 Power Flow Diagram
	5.31 Efficiency of a DC Machine
	5.32 Condition for Maximum Efficiency
	5.33 Test Performed to Determine Efficiency of DC Machines
	5.34 Brake Test
	5.35 Swinburne’s Test
	5.36 Hopkinson’s Test
	5.37 Testing of DC Series Machines
	5.38 Inspection/maintenance of DC Machines
	5.39 Faults in DC Machines
	5.40 Trouble Shooting in a DC Motor
	Section Practice Problems
	Review Questions
	Multiple Choice Questions
6. Synchronous Generators or Alternators
	Introduction
	6.1 General Aspects of Synchronous Machines
	6.2 Basic Principles
	6.3 Generator and Motor Action
	6.4 Production of Sinusoidal Alternating emf
	6.5 Relation between Frequency, Speed and Number of Poles
	6.6 Advantages of Rotating Field System over Stationary Field System
	6.7 Constructional Features of Synchronous Machines
	6.8 Excitation Systems
		6.8.1 DC Exciters
		6.8.2 Static-Excitation System
		6.8.3 Brushless Excitation System
	Section Practice Problems
	6.9 Armature Winding
	6.10 Types of Armature Winding
	6.11 Important Terms Used in Armature Winding
	Section Practice Problems
	6.12 Coil Span Factor
	6.13 Distribution Factor
	6.14 Winding Factor
	6.15 Generation of Three-phase emf
	6.16 emf Equation
	6.17 Wave Shape
	6.18 Harmonics in Voltage Wave Form
	Section Practice Problems
	6.19 Production of Revolving Field
	6.20 Ferrari’s Principle (Vector Representation of Alternating Field)
	6.21 Production of Two-phase Rotating Magnetic Field
	6.22 Production of Three-phase Rotating Magnetic Field
	6.23 Rating of Alternators
	6.24 Armature Resistance
	6.25 Armature Leakage Reactance
	6.26 Armature Reaction
	6.27 Effect of Armature Reaction on emf of Alternator
	6.28 Synchronous Reactance and Synchronous Impedance
	6.29 Equivalent Circuit of an Alternator and Phasor Diagram
	6.30 Expression for No-load Terminal Voltage
	6.31 Voltage Regulation
	6.32 Determination of Voltage Regulation
	6.33 Synchronous Impedance Method or emf Method
		6.33.1 Determination of Synchronous Impedance
		6.33.2 Determination of Synchronous Reactance
	6.34 Modern Alternators
	6.35 Short-Circuit Ratio (SCR)
	Section Practice Problems
	6.36 Assumptions Made in Synchronous Impedance Method
	6.37 Ampere-turn (or mmf) Method
	6.38 Zero Power Factor or Potier Method
	Section Practice Problems
	6.39 Power Developed by Cylindrical Synchronous Generators
	6.39.1 Power Output of an AC Generator (in Complex Form)
	6.39.2 Real Power Output of an AC Generator
	6.39.3 Reactive Power Output of an AC Generator
	6.39.4 Power Input to an AC Generator (in Complex Form)
	6.39.5 Real Power Input to an AC Generator
	6.39.6 Reactive Power Input to an AC Generator
	6.39.7 Condition for Maximum Power Output
	6.39.8 Condition for Maximum Power Input
	6.39.9 Power Equations, when Armature Resistance is Neglected
	6.40 Two-Reactance Concept for Salient Pole Synchronous Machines
		6.40.1 Determination of Xd and Xq by Low Voltage Slip Test
	6.41 Construction of Phasor Diagram for Two-Reaction Concept
	6.42 Power Developed by a Salient Pole Synchronous Generator
	Section Practice Problems
	6.43 Transients in Alternators
		6.43.1 Sub-transient, Transient and Direct Reactance
	6.44 Losses in a Synchronous Machine and Efficiency
	6.45 Power Flow Diagram
	6.46 Necessity of Cooling
	6.47 Methods of Cooling
	6.48 Preventive Maintenance
	Section Practice Problems
	Review Questions
	Multiple Choice Questions
7. Parallel Operation of Alternators
	Introduction
	7.1 Necessity of Parallel Operation of Alternators
	7.2 Requirements for Parallel Operation of Alternators
	7.3 Synchronising Alternators
	7.4 Conditions for Proper Synchronising
	7.5 Synchronising Single-phase Alternators
		7.5.1 Dark Lamp Method
		7.5.2 Bright Lamp Method
	7.6 Synchronising Three-phase Alternators
		7.6.1 Three Dark Lamps Method
		7.6.2 Two Bright and One Dark Lamp Method
	7.7 Synchronising Three-phase Alternators using Synchroscope
	7.8 Shifting of Load
	7.9 Load Sharing between Two Alternators
	Section Practice Problems
	7.10 Two Alternators Operating in Parallel
	7.11 Synchronising Current, Power and Torque
	7.12 Effect of Change in Input Power of One of the Alternators
	7.13 Effect of Change in Excitation of One of the Alternators
	7.14 Effect of Reactance
	7.15 Effect of Governors’ Characteristics on Load Sharing
	7.16 Hunting
	Section Practice Problems
	Review Questions
	Multiple Choice Questions
8. Synchronous Motors
	Introduction
	8.1 Working Principle of a Three-Phase Synchronous Motor
	8.2 Effect of Load on Synchronous Motor
	8.3 Equivalent Circuit of a Synchronous Motor
	8.4 Phasor Diagram of a Synchronous Motor (Cylindrical Rotor)
	8.5 Relation between Supply Voltage V and Excitation Voltage E
	8.6 Different Torques in a Synchronous Motor
	8.7 Power Developed in a Synchronous Motor (Cylindrical Rotor)
	8.8 Phasor Diagrams of a Salient-pole Synchronous Motor
	8.9 Power Developed in a Salient-pole Synchronous Motor
	8.10 Power Flow in a Synchronous Motor
	Section Practice Problems
	8.11 Effect of Change in Excitation
	8.12 V-Curves and Inverted V-Curves
	8.13 Effect of Change in Load on a Synchronous Motor
	8.14 Methods of Starting of Synchronous Motors
	8.15 Synchronous Condenser
	8.16 Characteristics of Synchronous Motor
	8.17 Hunting
	8.18 Applications of Synchronous Motors
	8.19 Comparison between Three-phase Synchronous and Induction Motors
	8.20 Merits and Demerits of Synchronous Motor
	Section Practice Problems
	Review Questions
	Multiple Choice Questions
9. Three-Phase Induction Motors
	Introduction
	9.1 Constructional Features of a Three-Phase Induction Motor
	9.2 Production of Revolving Field
	9.3 Principle of Operation
	9.4 Reversal of Direction of Rotation of Three-Phase Induction Motors
	9.5 Slip
	9.6 Frequency of Rotor Currents
	9.7 Speed of Rotor Field or mmf
	9.8 Rotor emf
	9.9 Rotor Resistance
	9.10 Rotor Reactance
	9.11 Rotor Impedance
	9.12 Rotor Current and Power Factor
	9.13 Simplified Equivalent Circuit of Rotor
	Section Practice Problems
	9.14 Stator Parameters
	9.15 Induction Motor on No-load
	9.16 Induction Motor on Load
	9.17 Induction Motor vs Transformer
	9.18 Reasons of Low Power Factor of Induction Motors
	9.19 Main Losses in an Induction Motor
	9.20 Power Flow Diagram
	9.21 Relation between Rotor Copper Loss, Slip and Rotor Input
	9.22 Rotor Efficiency
	Section Practice Problems
	9.23 Torque Developed by an Induction Motor
	9.24 Condition for Maximum Torque and Equation for Maximum Torque
	9.25 Starting Torque
	9.26 Ratio of Starting to Maximum Torque
	9.27 Ratio of Full Load Torque to Maximum Torque
	9.28 Effect of Change in Supply Voltage on Torque
	9.29 Torque-slip Curve
	9.30 Torque-speed Curve and Operating Region
	9.31 Effect of Rotor Resistance on Torque-slip Curve
	Section Practice Problems
	9.32 Constant and Variable Losses in an Induction Motor
	9.33 Main Tests Performed on an Induction Motor
		9.33.1 Stator Resistance Test
		9.33.2 Voltage-ratio Test
		9.33.3 No-load Test
		9.33.4 Blocked Rotor Test
		9.33.5 Heat Run Test
	9.34 Equivalent Circuit of an Induction Motor
	9.35 Simplified Equivalent Circuit of an Induction Motor
	9.36 Maximum Power Output
	9.37 Circle Diagram
	9.38 Circle Diagram for the Approximate Equivalent Circuit of an Induction Motor
	9.39 Construction of a Circle Diagram for an Induction Motor
	9.40 Results Obtainable from Circle Diagram
	9.41 Maximum Quantities
	9.42 Significance of Some Lines in the Circle Diagram
	Section Practice Problems
	9.43 Effect of Space Harmonies
		9.43.1 Cogging in Three-phase Induction Motors
		9.43.2 Crawling in Three-phase Induction Motors
	9.44 Performance Curves of Induction Motors
	9.45 Factors Governing Performance of Induction Motors
	9.46 High Starting Torque Cage Motors
		9.46.1 Deep Bar Cage Rotor Motors
		9.46.2 Double Cage Induction Motor
	9.47 Motor Enclosures
	9.48 Standard Types of Squirrel Cage Motor
		9.48.1 Class A Motors
		9.48.2 Class B Motors
		9.48.3 Class C Motors
		9.48.4 Class D Motors
		9.48.5 Class E Motors
		9.48.6 Class F Motors
	9.49 Advantages and Disadvantages of Induction Motors
		9.49.1 Squirrel Cage Induction Motors
		9.49.2 Slip-ring Induction Motors
	9.50 Applications of Three-phase Induction Motors
	9.51 Comparison of Squirrel Cage and Phase Wound Induction Motors
	9.52 Comparison between Induction Motor and Synchronous Motor
	9.53 Installation of Induction Motors
	9.54 Preventive Maintenance of Three-phase Induction Motors
	Section Practice Problems
	Review Questions
	Multiple Choice Questions
10. Starting Methods and Speed Control of Three-phase Induction Motors
	Introduction
	10.1 Necessity of a Starter
	10.2 Starting Methods of Squirrel Cage Induction Motors
		10.2.1 Direct on Line (D.O.L.) Starter
		10.2.2 Stator Resistance (or Reactance) Starter
		10.2.3 Star-Delta Starter
		10.2.4 Auto-transformer Starter
	10.3 Rotor Resistance Starter for Slip Ring Induction Motors
	Section Practice Problems
	10.4 Speed Control of Induction Motors
	10.5 Speed Control by Changing the Slip
		10.5.1 Speed Control by Changing the Rotor Circuit Resistance
		10.5.2 Speed Control by Controlling the Supply Voltage
		10.5.3 Speed Control by Injecting Voltage in the Rotor Circuit
	10.6 Speed Control by Changing the Supply Frequency
	10.7 Speed Control by Changing the Poles
	10.8 Speed Control by Cascade Method
	10.9 Speed Control by Injecting an emf in the Rotor Circuit
		10.9.1 Kramer System of Speed Control
		10.9.2 Scherbius System of Speed Control
	Section Practice Problems
	Review Questions
	Multiple Choice Questions
11. Single-Phase Motors
	Introduction
	11.1 Classification of Single-phase Motors
	11.2 Single-phase Induction Motors
	11.3 Nature of Field Produced in Single Phase Induction Motors
	11.4 Torque Produced by Single-phase Induction Motor
	11.5 Equivalent Circuit of Single-phase Induction Motor
	11.6 Rotating Magnetic Field from Two-phase Supply
	11.7 Methods to make Single-phase Induction Motor Self-starting
	11.8 Split Phase Motors
	11.9 Capacitor Motors
	Section Practice Problems
	11.10 Shaded Pole Motor
	11.11 Reluctance Start Motor
	11.12 Single-phase Synchronous Motors
	11.13 Reluctance Motors
	11.14 Hysteresis Motors
	11.15 AC Series Motor or Commutator Motor
	11.16 Universal Motor
	11.17 Comparison of Single-phase Motors
	11.18 Trouble Shooting in Motors
	Section Practice Problems
	Review Questions
	Multiple Choice Questions
12. Special Purpose Machines
	Introduction
	12.1 Feedback Control System
	12.2 Servomechanism
	12.3 Servomotors
	12.4 DC Servomotors
		12.4.1 Field-controlled DC Servomotors
		12.4.2 Armature-controlled DC Servomotors
		12.4.3 Series Split-field DC Servomotors
		12.4.4 Permanent-magnet Armature-controlled DC Servomotor
	12.5 AC Servomotors
	12.6 Schrage motor
	Section Practice Problems
	12.7 Brushless Synchronous Generator
		12.7.1 Brushless DC Generator
	12.8 Brushless Synchronous Motor
	12.9 Three-brush (or Third-brush) Generator
	12.10 Brushless DC Motors
	12.11 Stepper Motors
		12.11.1 Permanent-magnet (PM) Stepper Motor
		12.11.2 Variable-reluctance (VR) Stepper Motor
	Section Practice Problems
	12.12 Switched Reluctance Motor (SRM)
	12.13 Linear Induction Motor (LIM)
	12.14 Permanent Magnet DC Motors
	12.15 Induction Generator
	12.16 Submersible Pumps and Motors
	12.17 Energy Efficient Motors
	Section Practice Problems
	Review Questions
	Multiple Choice Questions
Open Book Questions
Index