JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD

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 transformers- equivalent circuit - comparison with two winding transformers. Polyphase transformers - Polyphase connections - Y/Y, Y/, /Y, / and open

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” 3 rd 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.