Electrical Machines I

Course Objectives
To introduce and apply electric magnetic circuit concepts to electromechanical energy conversion to explain and predict the performance of basic devices such as transformer, electromagnets and rotating electric machines.

1.0 Magnetic Circuit Concepts: (5 hours)
1.1 Ohm’s law for magnetic circuits
1.2 Magnetic potential sources, electric current, permanent magnetic materials
1.3 Ferromagnetic materials, magnetic saturation, non-linearity, Hysterisis
1.4 Series and parallel magnetic circuits
1.5 Effect of air gaps
1.6 DC and AC excitation, Hysterisis and eddy currents, energy loss, laminations, sintered core
1.7 Self and mutual inductances
1.8 Force due to magnetic effects, electromagnets.

2.0 Transformer: (8 hours)
2.1 Magnetic circuits of transformer, transformer steels
2.2 Ideal transformers
2.3 Mutual inductance and coupled model of transformers
2.4 Air core Vs iron core transformers
2.5 Two winding transformers
2.6 Equivalent circuit of power transformers
2.7 Evaluation of Equivalent circuit parameters from open circuit and short circuit tests
2.8 Excitation consideration: core losses, current harmonics
2.9 Equivalent circuit calculation: voltage regulation and efficiency
2.10 Polarity of windings
2.11 Series and parallel connection of windings
2.12 Audio transformers Vs power transformers
2.13 Auto transformers
2.14 Instrumentation transformers – PTs, CTs
2.15 Three phase transformer connection
2.16 V-V and open delta connection
2.17 T-T connections
2.18 Scott 3 phase to 2 phase connections.

3.0 Principles of Electromechanical Energy Conversion: (2 hours)
3.1 Energy storage and retrieval from magnetic fields
3.2 Lenz’s law, Faraday’s laws, Fleming’s rule
3.3 Force and torque due to magnetic fields, principle of virtual work, the coenergy function
3.4 Interaction between electric, magnetic and mechanical systems

4.0 General Aspects of Modeling and Steady State Performance of DC machines: (4 hours)
4.1 DC machine constructional features
4.2 Magnetic circuit, air gap flux patterns
4.3 Mechanical rectification by commutator action
4.4 Torque Production and voltage generation
4.5 Armature windings, lap and wave windings
4.6 Field excitation: shunt, series and compound fields
4.7 Armature reaction
4.8 Commutation, interpoles.
4.9 Reversible energy flow between electrical and mechanical systems with a dc machine

5.0 DC Motors: (4 hours)
5.1 Torque/speed characteristics of shunt field, series field and compound field motors.
5.2 Effects of armature reaction on motor operation
5.3 Commutation problems, pole face compensating windings
5.4 Speed regulation and control in dc motors
5.5 Effect of field excitation and armature applied voltage on steady state performance of dc motors
5.6 Reversal of rotation of dc motors
5.7 Motor starting problems, limiting armature current inrush.

6.0 DC Generators: (4 hours)
6.1 Voltage/speed/load characteristics of dc generators
6.2 Shunt, series and compound field machines
6.3 Separate and self-excited machines, voltage build-up in self excited generators
6.4 Voltage regulation of generators

7.0 Control of DC Machines in the steadies-state: (3 hours)
7.1 Automatic voltage regulation of dc generators
7.2 Manual and automatic starting and speed control of motors, armature voltage and shunt field control.

8.0 Induction machines: (8 hours)
8.1 Construction and type
8.2 Rotating magnetic field and action of induction motor
8.3 Torque-slip characteristic
8.4 Losses and efficiency
8.5 Induction motor starter
8.6 Induction generator

9.0 Synchronous machines: (8 hours)
9.1 Basic structure of synchronous machines, salient pole and cylindrical rotor structure
9.2 Synchronous generators
9.2.1 Operating principle and emf equation
9.2.2 Speed and frequency relationship.
9.2.3 Synchronous generator on load, armature reaction, voltage regulation
9.2.4 Synchronization, generator connected to large system, infinite bus concept.
9.3 Synchronous motor
9.3.1 Operating principle
9.3.2 Starting methods
9.3.3 Effect of excitation, V-curve, inverted V-curve, power factor control
9.4 Power angle characteristic of cylindrical rotor machine
9.5 Two-reaction model of salient pole machine
9.6 Power angle characteristic cylindrical salient pole machine

Laboratory:
1) Magnetic Circuit Study.
- Calculate and measure BV & H for a magnetic circuit
- Compare the relative permeabilities of two different sample cores.
2) Two winding transformer
- Carry out o/c test and s/c test on a single phase transformer to evaluate equivalent circuit.
- Examine exciting current harmonics.
3) DC machine Study
- Study speed control using variable armature voltage and variable field current on dc shunt motor
- Study voltage regulation of a dc shunt generator
4) Induction machine study
- Measure torque-speed characters of a three phase induction motor
- Measure power factor and efficiency of the motor at various loading condition
5) Synchronous machine study
- Study of frequency and voltage control of a synchronous generator

Text books:
1) A. E. Fitzgerald, C. kingsley and S.D. Umans, “Electric Machinery” 4th ed. McGraw-Hill Book Company, New York 1983
2) Bhag S. Guru and Huseyin R. Hiziroglu, “Electric Machinory and Trans former”, Harcourt Brace Jovanovich, Inc., New York, 1988.