Electrical Machines
Course Objectives:
To impart knowledge on constructional details, operating principle and performance of Transformers, DC Machines, 1phase and 3phase Induction Machines, 3phase Synchronous Machines and Fractional Kilowatt Motors.
 Magnetic Circuits and Induction (4 hours)
 Magnetic Circuits
 Ohm’s Law for Magnetic Circuits
 Series and Parallel magnetic circuits
 Core with air gap
 BH relationship (Magnetization Characteristics)
 Hysteresis with DC and AC excitation
 Hysteresis Loss and Eddy Current Loss
 Faraday’s Law of Electromagnetic Induction, Statically and Dynamically Induced EMF
 Force on Current Carrying Conductor
 Transformer (8 hours)
 Constructional Details, recent trends
 Working principle and EMF equation
 Ideal Transformer
 No load and load Operation
 Operation of Transformer with load
 Equivalent Circuits and Phasor Diagram
 Tests: Polarity Test, Open Circuit test, Short Circuit test and Equivalent Circuit Parameters
 Voltage Regulation
 Losses in a transformer
 Efficiency, condition for maximum efficiency and all day efficiency
 Instrument Transformers: Potential Transformer (PT) and Current Transformer (CT)
 Auto transformer: construction, working principle and Cu saving
 Three phase Transformers
 DC Generator (6 hours)
 Constructional Details and Armature Winding
 Working principle and Commutator Action
 EMF equation
 Method of excitation: separately and self excited, Types of DC Generator
 Characteristics of series, shunt and compound generator
 Losses in DC generators
 Efficiency and Voltage Regulation
 DC Motor (6 hours)
 Working principle and Torque equation
 Back EMF
 Method of excitation, Types of DC motor
 Performance Characteristics of D.C. motors
 Starting of D.C. Motors: 3 point and 4 point starters
 Speed control of D.C. motors: Field Control, Armature Control
 Losses and Efficiency
 Three Phase Induction Machines (6 hours)
 Three Phase Induction Motor
 Constructional Details and Types
 Operating Principle, Rotating Magnetic Field, Synchronous Speed, Slip, Induced EMF, Rotor Current and its frequency, Torque Equation
 TorqueSlip characteristics
 Three Phase Induction Generator
 Working Principle, voltage build up in an Induction Generator
 Power Stages
 Three Phase Synchronous Machines (6 hours)
 Three Phase Synchronous Generator
 Constructional Details, Armature Windings, Types of Rotor, Exciter
 Working Principle
 EMF equation, distribution factor, pitch factor
 Armature Reaction and its effects
 Alternator with load and its phasor diagram
 Three Phase Synchronous Motor
 Principle of operation
 Starting methods
 No load and Load operation, Phasor Diagram
 Effect of Excitation and power factor control
 Fractional Kilowatt Motors (6 hours)
 Single phase Induction Motors: Construction and Characteristics
 Double Field Revolving Theory
 Split phase Induction Motor
 Capacitors start and run motor
 Reluctance start motor
 Alternating Current Series motor and Universal motor
 Special Purpose Machines: Stepper motor, Schrage motor and Servo motor
Practical:
1. Magnetic Circuits
 To draw BH curve for two different sample of Iron Core
 Compare their relative permeability
2. Two Winding Transformers
 To perform turn ratio test
 To perform open circuit (OC) and short circuit (SC) test to determine equivalent circuit parameter of a transformer and hence to determine the regulation and efficiency at full load
3. DC Generator
 To draw open circuit characteristic (OCC) of a DC shunt generator
 To draw load characteristic of shunt generator
4. DC Motor
 Speed control of DC Shunt motor by (a) armature control method (b) field control method
 To observe the effect of increasing load on DC shunt motor’s speed, armature current, and field current.
5. 3phase Machines
 To draw torquespeed characteristics and to observe the effect of rotor resistance on torquespeed characteristics of a 3phase Induction Motor
 To study load characteristics of synchronous generator with (a) resistive load (b) inductive load and (c) capacitive load
6. Fractional Kilowatt Motors
 To study the effect of a capacitor on the starting and running of a singlephase induction motor
 Reversing the direction of rotation of a single phase capacitor induct
References:
 I.J. Nagrath & D.P.Kothari,” Electrical Machines”, Tata McGraw Hill
 S. K. Bhattacharya, “Electrical Machines”, Tata McGraw Hill
 B. L. Theraja and A. K. Theraja, “Electrical Technology (VolII)”, S. Chand
 Husain Ashfaq ,” Electrical Machines”, Dhanpat Rai & Sons
 A.E. Fitzgerald, C.Kingsley Jr and Stephen D. Umans,”Electric Machinery”, Tata McGraw Hill
 B.R. Gupta & Vandana Singhal, “Fundamentals of Electrical Machines, New Age International
 P. S. Bhimbra, “Electrical Machines”’ Khanna Publishers
 Irving L.Kosow, “Electric Machine and Tranformers”, Prentice Hall of India.
 M.G. Say, “The Performance and Design of AC machines”, Pit man & Sons.
 Bhag S. Guru and Huseyin R. Hizirogulu, “Electric Machinery and Transformers” Oxford University Press, 2001.
Evaluation Scheme
The questions will cover all the chapters of syllabus. The evaluation scheme will be as indicated in the table below
Chapters 
Hours 
Marks Distribution* 
1 
4 
8 
2 
8 
16 
3 
6 
12 
4 
6 
12 
5 
6 
10 
6 
6 
10 
7 
6 
12 
Total 
42 
80 
*Note: There may be minor deviation in the marks distribution.
