Electrical Machines I

Course Objectives:
To impart knowledge on constructional details, operating principle and performance of Transformers, DC Machines, and 3-phase Induction Machines.

1. Magnetic Circuits and Induction(4 hours)
1. Magnetic Circuits: Series and Parallel Magnetic Circuits
2. Core with air gap
3. B-H relationship (Magnetization Characteristics)
4. Hysteresis with DC and AC excitation
5. Hysteresis Loss and Eddy Current Loss
6. Faraday’s Law of Electromagnetic Induction, Statically and Dynamically Induced EMF
7. Force on Current Carrying Conductor


2. Transformer(12 hours)
1. Constructional Details, recent trends
2. Working principle and EMF equation
3. Ideal Transformer
4. Mutual Inductance and Coupled Circuit model
5. No load and Load operation
6. Equivalent Circuits and Phasor Diagram
7. Capacity of Transformers
8. Exciting Current harmonics
9. Transformer Inrush Current
10. Tests: Polarity Test, Open Circuit Test, Short Circuit test
11. Voltage Regulation
12. Losses in a Transformer
13. Efficiency, condition for maximum efficiency and all day efficiency
14. Instrument Transformers: Potential Transformer (PT) and Current Transformer(CT)
15. Auto transformer: construction, working principle and Cu saving
16. Three phase Transformers
17. Three phase transformer connections: Υ/Υ, Υ/Δ, Δ/Υ, Δ/Δ and V/V (or open Δ)connections
18. Choice between star and delta connection, Choice of Transformer connections
19. Three phase to two phase conversion: Scott connection
20. Three winding Transformer
21. Parallel operation of single phase and three phase Transformers


3. DC Generator(7 hours)
1. Constructional Details and Armature Windings
2. Working principle and Commutator Action
3. EMF equation
4. Method of excitation: separately and self excited, Types of DC Generator
5. Characteristics of series, shunt and compound generator
6. Voltage build up in a self excited DC generator
7. Armature Reaction
8. Commutation: Interpoles and Compensating Windings
9. Losses in DC generators
10. Efficiency and Voltage Regulation


4. DC Motor(7 hours)
1. Working principle and Torque equation
2. Back EMF
3. Method of excitation, Types of DC Motor
4. Performance Characteristics of D.C. motors
5. Losses and Efficiency
6. Starting of D.C. Motors: 3 point and 4 point starters
7. Speed control of D.C. Motors: Field Control, Armature Control, Reversing of DC Motors


5. Three-Phase Induction Machines(12 hours)
1. Three Phase Induction Motor
2. Constructional Details and Types
3. Operating Principle, Rotating Magnetic Field, Synchronous Speed,
4. Slip, Induced EMF, Rotor Current and its frequency, Torque Equation
5. Torque-Slip characteristics, Effect of rotor resistance on Torque-Slip characteristics
6. Testing of Induction Motor
7. Losses, Power stages and Efficiency
8. Starting Methods
9. Speed Control Methods
10. Double Cage Induction Motor
11. Three Phase Induction Generator
1. Working Principle, voltage build up in an Induction Generator
2. Power Stages
3. Isolated and Grid connected mode

References:

1. I.J. Nagrath & D.P.Kothari,” Electrical Machines”, Tata McGraw Hill
2. S. K. Bhattacharya, “Electrical Machines”, Tata McGraw Hill
3. Husain Ashfaq ,” Electrical Machines”, Dhanpat Rai & Sons
4. A.E. Fitzgerald, C.Kingsley Jr and Stephen D. Umans,”Electric Machinery”, Tata McGraw Hill
5. P. S. Bhimbra, “Electrical Machines”’ Khanna Publishers
6. Irving L.Kosow, “Electric Machine and Tranformers”, Prentice Hall of India.
7. M.G. Say, “The Performance and Design of AC machines”, Pit man & Sons.
8. Bhag S. Guru and Huseyin R. Hizirogulu, “Electric Machinery and Transformers”
9. Oxford University Press, 2001.

Practical:

1. Magnetic Circuits
1. To draw B-H curve for two different sample of Iron Core
2. Compare their relative permeabilities
2. Two Winding Transformers
1. To perform turn ratio test
2. 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. To examine exciting current harmonics
3. DC Generator
1. 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
2. To draw load characteristic of shunt generator
4. DC Motor
1. Speed control of DC Shunt motor by (a) armature control method (b) field control method
2. To observe the effect of increasing load on DC shunt motor’s speed, armature current, and field current.
5. 3-phase Induction Machines
1. To draw torque-speed characteristics and to observe the effect of rotor resistance on torque-speed characteristics
2. 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.