ELECTRICAL MACHINES – II(Syllabus 2-2)

ELECTRICAL MACHINES – II

Objective :

As an extension of Electrical machines I course this subject facilitates to study of the performance of Transformers and Induction motors which are the major part of industrial drives and agricultural pump sets.

UNIT-I    Single Phase Transformers – Construction & Operation

Single phase transformers-types - constructional details-minimization of hystersis and eddy current losses-emf equation - operation on no load and on load - phasor diagrams

UNIT-II   Single Phase Transformers - Performance

 Equivalent circuit - losses and efficiency-regulation. All day efficiency - effect of variations of frequency & supply voltage on iron losses.

UNIT-III  Testing of Single Phase Transformer and Autotransformer

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.

UNIT-IV  Polyphase Transformers

Polyphase transformers - Polyphase connections - Y/Y, Y/D, D/Y, D/D and open D, Third harmonics in phase voltages-three winding transformers-tertiary windings-determination of Zp, Zs and Zt transients in switching - off load and on load tap changing; Scott connection.

UNIT-V   Polyphase Induction Motors

Polyphase induction motors-construction details of cage and wound rotor machines-production of a rotating magnetic field - principle of operation - rotor emf and rotor frequency - rotor reactance, rotor current and pf at standstill and during operation.

UNIT-VI  Characteristics of Induction Motors

Rotor power input, rotor copper loss and mechanical power developed and their inter relation-torque equation-deduction from torque equation - expressions for maximum torque and starting torque - torque slip characteristic - double cage and deep bar rotors - equivalent circuit - phasor diagram - crawling and cogging

UNIT-VII Circle Diagram of Induction Motors

Circle diagram-no load and blocked rotor tests-predetermination of performance-methods of starting and starting current and torque calculations

UNIT-VIII                Speed Control Methods

Speed control-change of frequency; change of poles and methods of consequent poles; cascade connection. injection of  an emf into rotor circuit (qualitative treatment only)-induction generator-principle of operation.

TEXT BOOKS:

1. Electric machinery - A.E. Fitzgerald, C.Kingsley and S.Umans, Mc Graw Hill             

      Companies, 5^th edition

2. Electrical machines-PS Bhimbra, Khanna Publishers.

REFERENCE BOOKS:

1.     Performance and Design of AC Machines by MG.Say, BPB Publishers

2.     Theory of Alternating Current Machinery- by Langsdorf, Tata McGraw-Hill Companies, 2^nd edition.

3.     Electric Machines –by I.J.Nagrath & D.P.Kothari,Tata Mc Graw Hill, 7^th  Edition.2005

4.     Electromechanics-II (transformers and induction motors) S. Kamakashaiah Hitech publishers.