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Electrical Machines

Electrical Machines
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GATE SYLLABUS

Electrical Machines:
Single phase transformer – equivalent circuit, phasor diagram, tests, regulation and efficiency; three phase transformers – connections, parallel operation; auto-transformer; energy conversion principles; DC machines – types, windings, generator characteristics, armature reaction and commutation, starting and speed control of motors; three phase induction motors – principles, types, performance characteristics, starting and speed control; single phase induction motors; synchronous machines – performance, regulation and parallel operation of generators, motor starting, characteristics and applications; servo and stepper motors.

JNTU SYLLABUS

ELECTRICAL MACHINES - I

UNIT – I Electromechanical Energy Conversion:
Electromechanical Energy conversion – forces and torque in magnetic field systems – energy balance –energy and force in a singly excited magnetic field system, determination of magnetic force - co-energy – multi excited magnetic field systems.

UNIT–II D.C.Generators – Construction & Operation:
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 – Problems

UNIT–III Armature reaction in D.C. Generator:
Armature reaction – Cross magnetizing and de-magnetizing AT/pole – compensating winding –commutation – reactance voltage – methods of improving commutation.

UNIT-IV Types of D.C Generators:
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.

UNIT–V Load Characteristics of Generators:
Load characteristics of shunt, series and compound generators – parallel operation of d.c series generators – use of equalizer bar and cross connection of field windings – load sharing.

UNIT-VI D.C. Motors:
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.

UNIT – VII Speed control of D.C. Motors:
Speed control of d.c. Motors: Armature voltage and field flux control methods. Ward-Leonard system. Principle of 3 point and 4 point starters – protective devices.

UNIT – VIII Testing of D.C. Machines:
Testing of d.c. machines: Losses – Constant & Variable losses – calculation of efficiency – condition for maximum efficiency Methods of Testing – direct, indirect and regenerative testing – brake test – Swinburne’s test –Hopkinson’s test – Field’s test – Retardation test – separation of stray losses in a d.c. motor test.

ELECTRICAL MACHINES – II

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/∆,∆/Y,∆/∆and open∆, 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.

ELECTRICAL MACHINES – III 

UNIT – I Construction and Principle of operation:
Constructional Features of round rotor and salient pole machines – Armature windings – Integral slot and fractional slot windings; Distributed and concentrated windings – distribution, pitch and winding factors – E.M.F Equation.

UNIT-II Synchronous Generator Characteristics:
Harmonics in generated e.m.f. – suppression of harmonics – armature reaction - leakage reactance –synchronous reactance and impedance – experimental determination - phasor diagram – loadcharacteristics.

UNIT – III Regulation of Synchronous Generator:
Regulation by synchronous impedance method, M.M.F. method, Z.P.F. method and A.S.A. methods –salient pole alternators – two reaction analysis – experimental determination of Xd and Xq (Slip test) Phasor diagrams – Regulation of salient pole alternators.

UNIT – IV Parallel Operation of Synchronous Generator:
Synchronizing alternators with infinite bus bars – synchronizing power torque – parallel operation and load sharing - Effect of change of excitation and mechanical power input. Analysis of short circuit current wave form – determination of sub-transient, transient and steady state  reactances.

UNIT – V Synchronous Motors – Principle of Operation:
Theory of operation – phasor diagram – Variation of current and power factor with excitation –synchronous condenser – Mathematical analysis for power developed .

UNIT-VI Power Circles:
Excitation and power circles – hunting and its suppression – Methods of starting – synchronous induction motor.

UNIT – VII Single Phase Motors:
Single phase Motors: Single phase induction motor – Constructional features-Double revolving field theory – Elementary idea of cross-field theory – split-phase motors – shaded pole motor.

UNIT – VIII Special Motors:
Principle & performance of A.C. Series motor-Universal motor – Principle of permanent magnet and reluctance motors.

Speech recognition technology is used more and more for telephone applications like travel booking and information, financial account information, customer service call routing, and directory assistance. Using constrained grammar recognition, such applications can achieve remarkably high accuracy. Research and development in speech recognition technology has continued to grow as the cost for implementing such voice-activated systems has dropped and the usefulness and efficacy of these systems has improved. For example, recognition systems optimized for telephone applications can often supply information about the confidence of a particular recognition, and if the confidence is low, it can trigger the application to prompt callers to confirm or repeat their request. Furthermore, speech recognition has enabled the automation of certain applications that are not automatable using push-button interactive voice response (IVR) systems, like directory assistance and systems that allow callers to "dial" by speaking names listed in an electronic phone book.

Speaker identity is correlated with the physiological and behavioral characteristics of the speaker. These characteristics exist both in the spectral envelope (vocal tract characteristics) and in the supra-segmental features (voice source characteristics and dynamic features spanning several segments). The most common short-term spectral measurements currently used are Linear Predictive Coding (LPC)-derived cepstral coefficients and their regression coefficients. A spectral envelope reconstructed from a truncated set of cepstral coefficients is much smoother than one reconstructed from LPC coefficients.

Therefore it provides a stabler representation from one repetition to another of a particular speaker's utterances. As for the regression coefficients, typically the first- and second-order coefficients are extracted at every frame period to represent the spectral dynamics. These coefficients are derivatives of the time functions of the cepstral coefficients and are respectively called the delta- and delta-delta-cepstral coefficients.

Speech recognition technology is used more and more for telephone applications like travel booking and information, financial account information, customer service call routing, and directory assistance. Using constrained grammar recognition, such applications can achieve remarkably high accuracy. Research and development in speech recognition technology has continued to grow as the cost for implementing such voice-activated systems has dropped and the usefulness and efficacy of these systems has improved. For example, recognition systems optimized for telephone applications can often supply information about the confidence of a particular recognition, and if the confidence is low, it can trigger the application to prompt callers to confirm or repeat their request. Furthermore, speech recognition has enabled the automation of certain applications that are not automatable using push-button interactive voice response (IVR) systems, like directory assistance and systems that allow callers to "dial" by speaking names listed in an electronic phone book.

Speaker identity is correlated with the physiological and behavioral characteristics of the speaker. These characteristics exist both in the spectral envelope (vocal tract characteristics) and in the supra-segmental features (voice source characteristics and dynamic features spanning several segments). The most common short-term spectral measurements currently used are Linear Predictive Coding (LPC)-derived cepstral coefficients and their regression coefficients. A spectral envelope reconstructed from a truncated set of cepstral coefficients is much smoother than one reconstructed from LPC coefficients.

Therefore it provides a stabler representation from one repetition to another of a particular speaker's utterances. As for the regression coefficients, typically the first- and second-order coefficients are extracted at every frame period to represent the spectral dynamics. These coefficients are derivatives of the time functions of the cepstral coefficients and are respectively called the delta- and delta-delta-cepstral coefficients.

ELECTRICAL MACHINES – I

TEXT BOOKS:

1. Electric Machinary – A. E. Fritzgerald, C. Kingsley and S. Umans, Mc Graw-Hill Companies, 5th editon

2. Electrical Machines – P.S. Bimbra., Khanna Publishers

REFERENCE BOOKS:

1.Performance and Design of D.C Machines by Clayton & Hancock, BPB Publishers

2.Electrical Machines -S.K. Battacharya,

3.Electric Machines by I.J. Nagrath & D.P. Kothari, Tata Mc Graw – Hill Publishers, 3rd edition, 2004.

4.Electromechanics – I (D.C. Machines) S. Kamakshaiah Hi-Tech Publishers.

ELECTRICAL MACHINES – II

TEXT BOOKS:

1. Electric machinery - A.E. Fitzgerald, C.Kingsley and S.Umans, Mc Graw HillCompanies, 5th 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, 2nd edition.

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

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

ELECTRICAL MACHINES – III

TEXT BOOKS:

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

2. Electrical Machines – by P.S. Bimbra, Khanna Publishers.

REFERENCE BOOKS:

1.The Performance and Design of A.C.Machines – by M.G.Say, ELBS and Ptiman & Sons.

2.Electric Machinery – by A.E. Fitzgerald, C.Kingsley and S.Umans, Mc Graw-Hill Companies, 5th edition, 1990.

3.Theory of Alternating Current Machinery by Langsdorf, Tata Mc Graw-Hill, 2nd edition.

4.Electromachanics-III (Synchronous and single phase machines), S.Kamakashiah, RightPublishers