EE303ES: ELECTRICAL MACHINES – I
B.Tech. II Year I Sem. L T P C
4 1 0 4

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Prerequisite: Basic electrical & Electronics Engineering

Course Objectives:

• To study and understand different types of DC generators, Motors and Transformers, their construction, operation and applications.
• To analyze performance aspects of various testing methods.

Course Outcomes: After this course, the student will be able to

• Identify different parts of a DC machine & understand its operation
• Carry out different testing methods to predetermine the efficiency of DC machines
• Understand different excitation and starting methods of DC machines
• Control the voltage and speed of a DC machines

UNIT – I

D.C. Generators: Principle of operation – Action of commutator – constructional features – armature windings – lap and wave windings – simplex and multiplex windings – use of laminated armature – E. M.F Equation.
Armature reaction – Cross magnetizing and de-magnetizing AT/pole – compensating winding – commutation – reactance voltage – methods of improving commutation. Methods of Excitation – separately excited and self excited generators – build-up of E.M.F - critical field resistance and critical speed - causes for failure to self excite and remedial measures. Load characteristics of shunt, series and compound generators

UNIT – II

D.C Motors: Principle of operation – Back E.M.F. - Torque equation – characteristics and application of shunt, series and compound motors – Armature reaction and commutation. Speed control of D.C. Motors - Armature voltage and field flux control methods. Motor starters (3 point and 4 point starters) Testing of D.C. machines - Losses – Constant & Variable losses – calculation of efficiency – condition for maximum efficiency.

UNIT - III

Methods of Testing – direct, indirect, and regenerative testing – Brake test – Swinburne’s test – Hopkinson’s test – Field’s test - separation of stray losses in a d.c. motor test.

UNIT - IV

Single phase transformers: Types - constructional details-minimization of hysteresis and eddy current losses- EMF equation - operation on no load and on load - phasor diagrams Equivalent circuit - losses and efficiency – regulation - All day efficiency - effect of variations of frequency & supply voltage on iron losses.

UNIT - V

OC and SC tests - Sumpner’s test - predetermination of efficiency and regulation-separation of losses test-parallel operation with equal and unequal voltage ratios - auto transformersequivalent circuit - comparison with two winding transformers.
Polyphase transformers - Polyphase connections - Y/Y, Y/Δ, Δ/Y, Δ/Δ and open Δ

TEXT BOOKS:

1. “I.J. Nagrath & D.P. Kothari”, “Electric Machines”, Tata Mc Graw Hill Publishers, 3rd edition, 2004.
2. “P.S. Bimbra”, “Electrical Machines”, Khanna Publishers, 7th Edition, 2014.

REFERENCE BOOKS:

1. E. Clayton & N. M. Hancock “The Performance and Design Of Direct Current Machines” 3rd Edition Pitman, London 1959.
2. “A. E. Fritzgerald, C. Kingsley and S. Umans”, “Electric Machinary”, McGraw Hill Companies, 6th edition, 2003.
3. “Abhijith Chakrabarthi & SubithaDebnath”, “Electrical Machines”, Mc Graw Hill, 2015.