Electrical Machines I
Course Objectives:
To impart knowledge on constructional details, operating principle and performance of Transformers, DC Machines, and 3phase Induction Machines.
 Magnetic Circuits and Induction(4 hours)
 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(12 hours)
 Constructional Details, recent trends
 Working principle and EMF equation
 Ideal Transformer
 Mutual Inductance and Coupled Circuit model
 No load and Load operation
 Equivalent Circuits and Phasor Diagram
 Capacity of Transformers
 Exciting Current harmonics
 Transformer Inrush Current
 Tests: Polarity Test, Open Circuit Test, Short Circuit test
 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
 Three phase transformer connections: Υ/Υ, Υ/Δ, Δ/Υ, Δ/Δ and V/V (or open Δ)connections
 Choice between star and delta connection, Choice of Transformer connections
 Three phase to two phase conversion: Scott connection
 Three winding Transformer
 Parallel operation of single phase and three phase Transformers
 DC Generator(7 hours)
 Constructional Details and Armature Windings
 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
 Voltage build up in a self excited DC generator
 Armature Reaction
 Commutation: Interpoles and Compensating Windings
 Losses in DC generators
 Efficiency and Voltage Regulation
 DC Motor(7 hours)
 Working principle and Torque equation
 Back EMF
 Method of excitation, Types of DC Motor
 Performance Characteristics of D.C. motors
 Losses and Efficiency
 Starting of D.C. Motors: 3 point and 4 point starters
 Speed control of D.C. Motors: Field Control, Armature Control, Reversing of DC Motors
 ThreePhase Induction Machines(12 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, Effect of rotor resistance on TorqueSlip characteristics
 Testing of Induction Motor
 Losses, Power stages and Efficiency
 Starting Methods
 Speed Control Methods
 Double Cage Induction Motor
 Three Phase Induction Generator
 Working Principle, voltage build up in an Induction Generator
 Power Stages
 Isolated and Grid connected mode
References:
 I.J. Nagrath & D.P.Kothari,” Electrical Machines”, Tata McGraw Hill
 S. K. Bhattacharya, “Electrical Machines”, Tata McGraw Hill
 Husain Ashfaq ,” Electrical Machines”, Dhanpat Rai & Sons
 A.E. Fitzgerald, C.Kingsley Jr and Stephen D. Umans,”Electric Machinery”, Tata McGraw Hill
 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.
Practical:
 Magnetic Circuits
 To draw BH curve for two different sample of Iron Core
 Compare their relative permeabilities
 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
 To examine exciting current harmonics
 DC Generator
 To draw open circuit characteristic (OCC) of a DC shunt generator and to calculate: (a)Maximum voltage built up (b)Critical resistance and critical speed of the machine
 To draw load characteristic of shunt generator
 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.
 3phase Induction Machines
 To draw torquespeed characteristics and to observe the effect of rotor resistance on torquespeed characteristics
 To perform no load and blocked rotor test to evaluate equivalent circuit parameters
Evaluation Scheme:
The questions will cover all the chapters of the syllabus. The evaluation scheme will be as indicates in the table below.
Chapter 
Hours 
Marks Distribution* 
1 
4 
8 
2 
12 
24 
3 
7 
12 
4 
7 
12 
5 
12 
24 
Total 
42 
80 
*Note: There may be a minor deviation in marks distribution.
