COURSE PLANNER

SUBJECT:AC MACHINES(2140906)

B.E. – Second Year

Class–Electrical 2015

Term: 16/2 (DEC-16 to APR-17)

Faculty:PROF. C. D. DESAI PROF. A. S. SHAH PROF. P. D. SOLANKI PROF. N. B. KANTHARIA PROF. V. B. RATHOD

Contents: 1. Course Outcomes 2. Course Contents[Syllabus] 3. List of Reference Books 4. List of Experiments

5. Major Equipments required for Experiments 6. List of Open source software and learning websites required for

experiments 7. Active Learning Assignments and Tutorial.

Instructionsfor Assignment/Tutorial:

[1] This set of Assignment-Tutorial consist the collection of questions of past GTU Question

papers.

[2] Attend those questions which are bold marked and/or frequently asked in GTU exam.

[3] Students should make a separate Chapter wise Files [write on File Pages] to solve these

Questions.

[4] Students must solve these given set of Assignments by themselves only.

[5] Assessment of given assignment should be done regularly after completion of each

chapter by Students from the respective faculty members.

[1] Course Outcomes:

After the completion of this course, the student shall able to do

1. Explain the construction, working principle, performance and applications of Poly-phase

induction motor,

2. Gain Knowledge about Single phase motors, synchronous generator (Alternator),

synchronous motor and commutator motors.

3. Differentiate between the concept about Synchronous and Asynchronous Machines.

4. Perform experiments on above machines.

5. Describe the need of these machines in the society.

6. Identify, formulate and solve the numerical problems related to above machines.

[2] Course Contents:

CHAPTER

NO. SYLLABUS Teaching

Hrs.

Module Weightage

1

Polyphase Induction Motor: Construction, Types of motor, Working principle, Rotating magnetic field. Operating parameters at different load, No-load & blocked rotor test, Equivalent circuit, Phasor diagram, Circlediagram, Efficiency and slip scale with the help of circle diagram, Effect of rotor resistance on performance of motor, Double cage motor and its equivalent circuit, Introduction to machine dynamics. Starters of poly-phase inductionmotor including soft starter, Methods of speed control of 3-phasemotor, Schematic diagram and advantages of Variable Voltage Variable Frequency drive. Electrical transients in induction machine, Magnetic levitation: Principle, advantages and application of linear induction motor. Effect of harmonics, Harmonic torques, Cogging &Crawling,Effect of unbalanced Voltages on performance of motor. Performance of motor with variable voltage and frequency. Testing of induction motor as per IS, Energy efficient motors.

20 35

2 Induction Generator: Principle of operation and application, Its load and p. f. control.

2 5

3

Single phase A. C. motors: Double field revolving theory, Starting & running performance of 1-phase induction Motor, Equivalent circuit of 1phaseinduction motor,Types of single phase motors, Principle and operation of split phase, Resistance start, Capacitor start and capacitor start & run induction motor, Shaded pole induction motor,Fractional horse power motors

6 10

4

Synchronous Machines: Construction, Types, Applications, Working principle.Equation of induced emf with and without harmonics in MMF, pitch factor and distribution factor, MMF of distributed windings, Torque equation Machine efficiency, Armature reaction and its compensation, Short circuit ratio, Effect of change in excitation, Effect of change in torque and speed, Voltage regulation, Determination of voltage regulation by Synchronous impedance method, MMF method, ZPF method and AIEE method, Synchronization : Importance and Methods of synchronization. Operating characteristic, Load angle and Power flow equations,Capability curves, Two reaction model of Salient pole machines, Parallel operation, Load sharing between parallel connected generators, Effect of unequal voltages & unequal percentage impedance, Governor characteristics, Introduction to single phase generators, Slip test for measurement of direct axis and quadrature axis reactance for salient pole machine Sudden short circuit of Synchronous machine, Hunting of synchronous machines and its prevention.

20 35

5

Synchronous motor: Methods of starting of synchronous motors, Different torques inSynchronous motor, Stability, Synchronous condenser, Synchronous phase modifiers, V-curves and O-curves of Synchronous motors. Auto Synchronous Motor: Construction, principle of operation, equivalent excitation current fordifferent rotor connections, circle diagrams.

5 10

6 Commutator motors: Construction and working principle of Schrage motor, Universal motor and Repulsion motor

3 5

[3] List of Reference Books : 1. Electrical Machines - Nagarath& Kothari, Tata Macgraw hill Pub.

2. Electrical Machines - J. B. Gupta, S.K.Kataria& Sons.

3. Electrical Technology Vol II - B. L. Theraja, S chand publication.

4. Electrical Machines - P S Bhimbra, Khanna Pub.

5. Performance and Design of A.C. machines - M. G. Say, CBS pub.

6. Electrical machine Drives and Power System - Wildi, 6th Edition, Pearson Publications.

[4] List of Experiments :

SR.

NO. NAME OF PRACTICAL

1 To study the starting methods and starters of 3-phase induction motor.

2 To perform direct load test on 3 phase induction motor and determine efficiency

under various load condition.

3 To perform direct load test on alternator and find out voltage regulation

4 To find out voltage regulation of a 3-ø alternator by synchronous impedance method.

5 To perform no load and blocked rotor test of induction motor to draw circle

diagram and determine performance characteristics of 3-phase induction motor.

6 To perform the parallel operation of 3-ø alternator with infinite bus.

7 To perform the V- curve and inverted V-curve of a synchronous motor.

8 To perform the operation of single phase induction motor.

9 To Perform the operation of [1]Repulsion Motor & [2]Universal Motor

10

To study the special machines

[1] PMBLDC motor

[2] induction voltage regulation

[3]linear induction motor

[4]energy efficient motor

[5]Major Equipments required for Experiments: 1. Moving Iron Precision Grade Voltmeter (Ac)

Range :0 -300-600 V 0-250-500 V

2. Moving Iron Type Meters Voltmeters [Dual Scale] Range :0 - 125-250 Volts

3. Moving Iron Type Meters (Ac/Dc) Ammeters [Dual Scale]

Range : 0 - 5 - 10 Amp 0 - 2 - 5 Amp

0-250-500 mAmp

4. 3-Ø Squiral Cage I.M. TEFC Star /Delta Connected

5. 1-Ø Induction Motor Capacitor Start And Run Induction Motor 6. 3-Ø Squirrel Cage Induction Motor And Dc Shunt Generator Set

7. Control Panel For 3-Ø Squirrel Cage Induction Motor And Dc Shunt Generator 8. 3-Ø Alternator And Dc Shunt Motor Set 9. Control Panel For 3-Ø Alternator And Dc Shunt Motor 10. Control Panel Set For 3 Phase Induction Motor 11. Control Panel Set For Single Phase Induction Motor

12. Rheostate

Range : 0-750 Ohm /1.2 Amp 0-470 Ohm/1.2 Amp

13. 1-Ф Power Factor Meter Analog Type

14. 1-Ф Power Factor Meter Digital Type

15. Frequency Meter Analog Type

16. Digital Indicator Type Synchroscope

600 V, Moving Vane Type

17. Universal Motor Ac Series Motor 1.0 Hp

18. Repulsion Motor 1.0 Hp

19. Galvanometer

Range:30-0-30

20. Phase Sequence Meter Rotating Disc Type

21. Energy Meter

22. Techometer, Analog Type

23. Portable Precision Grade Single Element Wattmeter Range:5/10 A,300/600

24. Digital Clamp-Meter

25. Auto State Continuously Variable Auto Transformer(3-Φ)

[6]List of Open source software and learning websites required for experiments : 1. Literature available on internet 2. Medical dictionaries 3. DELNET 4. Literature available in any laboratory manual of pharmaceutical industries. 5. MATLAB

[7]Learning Assignments /Tutorial:

CHAPTER-1

Polyphase Induction Motor: Construction, Types of motor, Working principle, Rotating magnetic field. Operating parameters at different load, No-load & blocked rotor test, Equivalent circuit, Phasor diagram, Circlediagram, Efficiency and slip scale with the help of circle diagram, Effect of rotor resistance on performance of motor, Double cage motor and its equivalent circuit, Introduction to machine dynamics. Starters of poly-phase induction motor including soft starter, Methods of speed control of 3-phasemotor, Schematic diagram and advantages of Variable Voltage Variable Frequency drive. Electrical transients in induction machine, Magnetic levitation : Principle, advantages and application of linear induction motor. Effect of harmonics, Harmonic torques, Cogging &Crawling,Effect of unbalanced Voltages on performance of motor. Performance of motor with variable voltage and frequency. Testing of induction motor as per IS, Energy efficient motors.

ATTEMPT SIX THEORIES:

SR

NO. QUESTION YEAR MARKS

1 Explain performance of 3-phase I.M. for change in supply frequency with constant supply voltage.

Dec-10 07

2 Explain effect of unequal supply voltage on performance of 3-phase I.M.

Dec-10 07

3

Derive the condition for maximum torque of Induction Motor.Also explain factors affecting maximum torque condition. OR Obtain an expression for the condition of maximum torque of an induction motor. Sketch and explain torque-slip curves for several values of rotor resistance and indicate the condition for maximum torque to be obtained at starting

Dec-10

May-14 07

4 Explain principle of magnetic levitation. Dec-10 07

5 Explain working principle and construction of induction motor. Also differentiate squirrel cage and slip ring induction motor

May-15

June-16 07

6 Draw the phasor diagram and equivalent circuit of a 3-phase induction motor.

June-11

June-14 07

7

How is high starting torque obtained by deep bar and double cage rotor construction? Describe their construction and also draw the equivalent circuit diagram of double cage Squirrel cage induction motor.

June-11

MAY-13

June-14

07

8 Differentiate between harmonic induction torque and harmonic synchronous torque developed in an induction motor. What are their effects?

June-11 07

9 Describe the construction, working and equivalent of a double-cage induction motor. Compare a single-cage and double-cage induction motors of the same ratings.

Dec-11

June-12 07

10

Explain the phenomena of crawling and cogging with their remedies. OR What is harmonic torques? Explain crawling and cogging for 3 phase induction motors.

Dec-11

June-12

May-13

June-14

May-15

June-16

07

11

Why starter is necessary for starting a 3-phase Induction motor?Discuss any two types of AC motor starters. OR List the different methods of starting an induction motor.

Dec-11

June-14

June-11

07

12

Discuss different methods of speed control of a 3–phase Induction motor.Explain anyone method of speed control of 3-phase slip ring induction motor from the rotorside. OR What is the need of speed control for an induction motor? Explain different speed control methods of induction motor.

Dec-11

June-12

May-13

June-14

May-15

07

13 Define acceleration time. Derive its expression using normal notationsof moment of inertia (J), optimum slip for minimum acceleration time(Smax,opt) etc.

Dec-11 07

14 Compare linear induction motor and conventional induction motors

Dec-11 07

15 Why the power factor of squirrel cage induction motor is low at light loadsand it improves as we increase the load on it.

June-12 02

16 Answer the following: June-12 04

a) State the difference between DOL starter and Star-delta starter.

b) Explain how by inserting resistance in the rotor circuit of a slip-ringinduction motor the starting current of the motor can belimited.

June-16

17 Explain the importance of Circle diagram of Polyphase Induction Motor.

NOV-13 07

18

Explain how rotating magnetic field is produced in 3-phase induction motor. OR Prove that when 3 phase supply is applied across the stator of 3 phase IM, a rotating magnetic field of constant magnitude is produced.

June-14

May-15 07

19 Give classification of A.C. Motors. Describe construction of Three phase Squirrel cage Induction motor with diagram May-14 07

20 What is slip? Explain torque-slip and torque-speed characteristics of an induction motor. May-15 07

21

Explain with reasons what happens when : a) The ends of rotor conductors of a squirrel cage

induction motor are kept open. b) In a 3-phase induction motor,the connections of any

two phases areinterchanged? c) If a 3-phase induction motor gets one of its 3-phase

opened? How will this beindicated? d) The 3-phase supply to the induction motor becomes

unbalanced. e) The supply voltage to the 3-phase induction motor

becomes too high [say600V] f) The supply voltage to the 3-phase induction motor

becomes too low [say200V]

June-11

07

22 Derive the equation of electromagnetic torque of three phase induction motor with usual notation from first principles.

June-16 07

23 Describe construction and working of linear induction motor

June-16 07

ATTEMPT SIX EXAMPLES:

SR

NO. QUESTION YEAR MARKS

1

A 25 HP, 415 V, 50 Hz, 4 poles, delta connected I.M. has the following impedances per phase in ohms referred to stator side. Stator resistance = 0.041 ohms, rotor resistance = 0.332 ohms, stator reactance = 1.106 ohms, rotor reactance = 0.464 ohms, magnetizing reactance = 26.30 ohms. Rotational losses are assumed constant = 1.1 KW. Core losses are neglected. If the slip = 3.2 % at rated voltage and frequency, find (1) Speed (2) Stator current (3) Power factor (4) Output and Input power (5) Percentage efficiency.

Dec-10 07

2

A 750 HP, 415 V, 3-phase, 50 Hz, 12 pole I.M. has a rotor impedance of (0.02+j0.15) ohms at standstill. Full load torque is obtained at 480 RPM. Calculate (1) Ratio of maximum to full load torque. (2) Speed at maximum torque. (3) Rotor resistance required to be added to get maximum starting torque.

Dec-10 07

3

A 3 phase 14.9 kW, 400 V, 4-pole IM gave the following test readings. No load : 400 V, 1250 W, 9 A Block rotor : 150 V, 4 KW, 38 A Draw circle diagram and find input current, speed, power factor, at full load. Also find maximum torque and power.

Dec-10

Dec-11 07

4

Draw the circle diagram of a 20 H.P, 400V, 50Hz, 3-phase star-connected induction motor from the following test data (line values): No load: 400V, 9A, p.f of 0.2 Block rotor: 20V, 50A, p.f of 0.4 From the circle diagram find

a) Line current and p.f at full load. b) Maximum power output.

June-11

June-14 07

5

A 415-V, 3-phase, 50 Hz, 4 pole star connected induction motor takes a line current of 11A with 0.85 p.f. lagging. Its total stator losses are 6% of the input. Rotor copper losses are 4% of the input to the rotor; mechanical losses are 3% of the rotor input. Calculate

a) Slip and rotor speed. b) Torque developed in therotor. c) Shaft torque

June-

12 07

6

A 230-V, 3-phase, 4-poles,50Hz, star connected induction motor is rated 3-KW. The equivalent circuit parameters are: R1=0.4 ohms, X1=0.9 ohms, R2’=0.4ohmsand X2’=0.7 ohms, X0=20 ohms. The stator core loss is 45 W and rotational loss is 100 W. For a slip of 0.03 find

a) Input current b) Power factor c) Air gap power d) Mechanical power e) Output power and efficiency.

June-12 07

7

Draw the circle the circle diagram for 5KW , 400-V, 3- _ ,4 pole 50 Hz, slip ring induction motor from the following data: No-load readings : 400 V , 5.2 A , 360W Blocked test readings : 95 V, 10 A, 700 W The ratio of primary to secondary turns is 2.62, Stator resistance per phase is 0.7 ohms and of the rotor is 0.175ohms. Calculate

a) Full-load current b) Full load slip c) Full- load power factor d) Rotor copper losses e) Stator copper loss f) Maximum torque in synch.watt g) Efficiency (h) Actual speed

June-

12 07

8

Draw the circle diagram for a 3-phase,6-pole,50hz,400 V star connected induction motor from the following data No load test: 400V, 9A, 1250 watt; Short circuit test: 200V, 50A, 6930 watt The stator loss at standstill is 55% of total copper losses and full load current is 32 A. determine (1) power factor , slip, output, efficiency, speed and torque at full load (2) starting torque

May-13 07

9

A 3-phase 6-pole,50 Hz , 400 V star connected induction motor has following test results. No-Load Test:- 400 V, 9 A, 1250 watts. Short-circuit Test:- 200 V, 50 A, 6930 watts. Determine the power scale using circle diagram

June-14 07

10

A 10 pole, 3 phase, 600 V, 50 Hz star connected IM has rotor resistance and standstill reactance of 0.03 and 0.5 ohms per phase respectively. Find (1) Speed at maximum torque (2) the ratio of full load torque to maximum torque, if the full load speed is 570rpm. 07

May-15 07

11

A 3 phase, 50 Hz, 500 V, I.M. with 8 poles gives an output of 30 kW at 700rpm with 0.8 PF lagging. The mechanical losses are equal to 1 kW. Find (1) slip (2) rotor copper loss (3) input if the stator losses are 1200 W and (4) line current.

May-15 07

Chapter-2 Induction Generator: Principle of operation and application, Its load and p. f. control.

ATTEMPT TWO THEORY:

SR

NO. QUESTION YEAR MARKS

1

Explain the operating principle of Induction Generator. Also mention itsapplication.

OR Explain the working principle of Induction Generator. Also discuss the applications of Induction generator.

Dec-10

June-

12

May-13

June-

14

May-15

June-

16

07

2

How can an induction generator feed power into a constant frequency bus? Give circuit configuration only. Also draw an approximate equivalent circuit diagram and Phasor diagram of induction generator.

June-

11 07

3

Discuss the working of Induction generator when connected to

a) Infinite bus b) Isolated load

June-11 07

Chapter-3

Single phase A. C. motors: Double field revolving theory, Starting & running performance of 1-phase induction Motor, Equivalent circuit of 1phaseinduction motor,Types of single phase motors, Principle and operation of split phase, Resistance start, Capacitor start and capacitor start & run induction motor, Shaded pole induction motor,Fractional horse power motors

ATTEMPT THREETHEORY:

SR

NO. QUESTION YEAR MARKS

1 Explain equivalent circuit of single phase Induction motor. Dec-10 07

2 Explain with winding and Phasor diagram, working of capacitor start and run 1-phase I.M.

Dec-10 07

3

Explain why plain single phase motor is not self-starting? List out the applications of different types of 1-phase I.M. OR Why a 1-phase Induction motor is not self-starting? Explain working of split phase type 1-phase Induction motor.

Dec-10

Dec-11

June-14

07

4

Justify the correctness of the following statements: a) A single phase induction motor, if provided with a

three phase slip ring type rotor connected to a starting resistance, results in a large starting torque.

b) Single-phase induction motor must have two starting windings.

Reversal of rotation of single phase I.M. is never a problem.

June-11 07

5

What is double-revolving theory? Draw equivalent circuit of 1-phase Induction motor for

a) Running condition. b) Starting condition.

Dec-11

June-14 07

6

Explain the working of a) Single phase Capacitor start & run Induction

motor b) Single phase Shaded pole Induction motor.

OR Explain working principle with necessary diagrams of any two single phase induction motors.

Dec-11

May-15

June-16

07

7 Draw the constructional features and operating characteristics of shaded pole motor. Also state its application.

June-12

MAY-13 07

8 Short Note on AC Series motor. June-12 3.5

9

Explain double revolving field theory related to 1-phase induction motor. From this theory verify that 1-phase induction motor is not self started. OR Why single phase induction motors are not self started? Explain double field revolving theory for single phase induction motor.

May-13

May-15

June-16

07

10

Explain different methods ofproducing starting torque in 1-phase induction motor OR Explain different methods of starting 1-phase induction motors.

MAY-13

June-14 07

ATTEMPT ALL EXAMPLES:

SR

NO. QUESTION YEAR MARKS

1

A 230V, 380W, 50Hz, 4-pole, 1-phase induction motor gave the following testresults. No load test : 230 V, 84 W, 2.8 A; Blocked rotor test: 110 V,460W, 6.2A The stator winding resistance is 4.6 ohm and during the blocked rotor test the auxiliary winding is open. Determine the equivalent circuit parameters.

MAY-13 07

Chapter-4 Synchronous Machines: Construction, Types, Applications, Working principle.Equation of induced emf with and without harmonics in MMF, pitch factor and distribution factor, MMF of distributed windings, Torque equation Machine efficiency, Armature reaction and its compensation, Short circuit ratio, Effect of change in excitation, Effect of change in torque and speed, Voltage regulation, Determination of voltage regulation by Synchronous impedance method, MMF method, ZPF method and AIEE method, Synchronization : Importance and Methods of synchronization. Operating characteristic, Load angle and Power flow equations,Capability curves, Two reaction model of Salient pole machines, Parallel operation, Load sharing between parallel connected generators, Effect of unequal voltages & unequal percentage impedance, Governor characteristics, Introduction to single phase generators, Slip test for measurement of direct axis and quadrature axis reactance for salient pole machine Sudden short circuit of Synchronous machine, Hunting of synchronous machines and its prevention.

ATTEMPT SIX THEORY:

SR

NO. QUESTION YEAR MARKS

1

What are the advantages of connecting alternators in

parallel? Explain with diagram three dark lamp method of

synchronizing two three phase alternators.

OR

State the conditions necessary for paralleling alternators.

Explain one dark and two bright lamp methods with

necessary electrical circuit diagram.

OR

State the condition and explain dark lamp method of

synchronizing of an alternator with busbar.

OR

State the conditions necessary for paralleling alternators. Explain

one dark and two bright lamp methods with necessary electrical

circuit diagram.

OR

Explain necessary conditions required for parallel operation of

two synchronous generator.

May-11

May-12

Jan-13

May-13

Nov-13

Dec-14

07

2

Explain coil span factor and distribution factor of an

alternator.

OR

Explain concept of pitch factor and distribution factor in case of an

May-11

Nov-11 07

alternator. How these values change with harmonics. Also explain

how e.m.f. in alternator can be evaluated when it contains non

sinusoidal variation of fluxes.

OR

Derive emf equation of alternator. Explain distribution factor

with effect of harmonics.

OR

Define pitch factor and distribution factor of an alternator.

Also derive the EMF equation of an alternator.

May-13

May-15

Jan-13

June-16

3

Briefly explain the ZPF method of finding the voltage

regulation of Alternator.

OR

List different methods for finding voltage regulation of an

alternator and explain Potier method.

OR

List different methods for finding voltage regulation of an

alternator and explain any one method.

OR

What is voltage regulation of an alternator? Explain any one

method to find out voltage regulation of an alternator.

OR

Explain synchronous impedance method of determining voltage

regulation of an alternator.

May-11

Jan-13

May-12

May-13

May-15

Dec-14

June-16

07

4

What is armature reaction? Explain the effect of armature reaction

on the terminal voltage of an alternator.

May-11

May-13

Nov-13

June-16

07

5

What are the causes of harmonics in the voltage waveform of an

alternator? How can these be minimized?

May-11

Jan-13

Nov-13

07

6

Explain the two reaction theory of salient pole synchronous

machine in detail with phasor diagram.

May-11

May-12

Jan-13

Nov-13

07

7 Discuss different torques in synchronous motor.

May-11 04

8 With necessary diagram explain the effect of leading power factor

on alternator.

Nov-11 07

9

Explain hunting of synchronous machines and methods of its

prevention.

Nov-11

Nov-13

June-16

07

10

Explain the effect of varying excitation at constant load on

synchronous motor.

OR

Explain the effect of varying excitation at constant load on

synchronousmotor.

Nov-11

May-13 07

11

Explain V and inverted V curves of synchronous motor

OR

Explain an experimental method of determining of ‘V’ curves for

a synchronous motor.

OR

Explain V-curves and its importance for synchronous motors.

OR

Explain an experimental method of determining ‘V’ curves for

a synchronous motor.

May-11

Nov-11

May-12

May-13

Nov-13

May-15

Jan-13

07

12

Why synchronous motor is not self starting? Explain the

methods of starting of synchronous motor.

Nov-11

May-12

May-13

Nov-13

07

13 Draw the combined Space and Time Phasor Diagram of Cylindrical

rotor alternators for the following conditions (i) lagging p.f. (ii)

leading p.f. and (iii) unity p.f.

May-12 07

14 Derive the expression for the input and output power developed

by synchronous motor. Also derive the maximum input and

output power developed by synchronous motor.

May-12

May-13 07

15

What do you mean by ‘Synchronous reactance’ in syn. Machine?

Explain why the synchronous impedance method gives a

regulation that is higher than the actual value in case of syn.

Generator.

Jan-13

07

16 Discuss the conditions to be satisfied for proper synchronization of

two alternators. May-15

07

17 Explain the working of synchronous phase modifier. Nov-13 07

18 Explain the difference between cylindrical and salient pole rotor

used in large alternator. Also explain pitch factor and distribution

factor.

Dec-14

June-16 07

ATTEMPT SIX EXAMPLES:

SR

NO. QUESTION YEAR

MARK

S

1

A 4 KVA, 3 phase, 110V, 50Hz, star connected alternator has Xd =

3 ohm and Xq = 2 ohms. The machine is delivering full load

current of 0.8 p.f. lagging at rated voltage. Find the induced emf,

load angle and maximum power output of the alternator.

Nov-11 07

2

A 220V, 50Hz, 6 pole star connected alternator with ohmic

resistance 0.06 ohm per phase, gave following data for open

circuit and full load zero power factor characteristics:

Field

Current (A) 0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.8

2.2

2.6

3.0

3.4

OC Voltage,

Ef (V) 29

.0

58

.0

87

.0

11

6

14

6

17

2

19

4

23

2

26

1.5

28

4

30

0

31

0

ZPF

Termial

Voltage (V)

--

--

--

--

--

0

29

88

14

0

17

7

20

8

23

0

Find the percentage voltage regulation at full load current of 40A

at power factor of 0.8 lag by ZPF method.

Nov-11

07

3

A 3 phase star connected 1000KVA, 11000V alternator has

rated current of 52.5 A.The ac resistance of the winding per

phase is 0.45 ohm. The test results are given below:

O.C. Test: field current = 12.5 A, voltage between lines = 422 V

S.C. Test : field current = 12.5A, line current = 52.5A

Determine the full load voltage regulation of the alternator

for

(i) 0.8 p.f lagging and

(ii) 0.8 p.f leading loads with synchronous impedance

method.

Nov-11

May-13 07

4

A 3 phase, 6 poles, 2.3 KV, 200KVA, star connected

synchronous motor has synchronous reactance of 12 ohm per

phase and negligible resistance. The motor is initially

operating at a load of 120KW with the field current adjusted

such that the armature current is minimum. The field current

is now increased such that the armature current is increased

by 50%. With this field current, the load is reduced to 60KW.

Calculate the new values of armature current and power

factor.

Nov-11 07

5

Calculate the r.m.s. value of the induced emf per phase of a 10-

pole, 3-phase, 50 Hz, star connected alternator with 2 slots per

pole per phase and 4 conductors per slot in two layers. The coil

span is 150 degree. The flux per pole has a fundamental

component of 0.12 Wb and 20% third harmonic component.

May-12 07

6

A star connected, 11 KV alternator, with synchronous impedance

of 1+j10 per phase is connected to infinite bus at rated voltage.

The alternator delivers an armature current of 100 A at unity

power factor to the bus bar. With the alternator output remaining

constant, the alternator excitation is increased by 15%. Find the

new values of armature current, load angle and p.f.

May-12 07

7

A 3.5 MVA, 3-phase synchronous generator rated at 6.6 KV

has 32 poles. Its direct and quadrature axis synchronous

reactances as measured by the slip test are 9.6 Ω and 6 Ω

respectively. Neglecting armature resistance, determine the

regulation and excitation emf needed to maintain 6.6 KV at

the terminals when supplying a load of 2.5 MW at 0.8 p.f.

lagging. What maximum power can generator supply at the

rated terminal voltage, if the field becomes open circuit?

May-12

May-13 07

8

A 2,000 KVA, 3-phase, 8-pole alternator runs at 750 rpm in

parallel with other machines on 6,000 V bus-bars. Find

synchronizing power on full load 0.8 p.f. lagging per mechanical

degree of displacement and the corresponding synchronizing

torque. The synchronous reactance is 6 ohm per phase.

May-12 07

9

A 60- KVA, 220 V, 50 Hz, single phase alternator has effective

armature resistance of 0.016 Ω and an armature leakage

reactance of 0.07 Ω. Compute the voltage induced in the

armature when the alternator is delivering rated current at a

load p.f. of (a) unity (b) 0.7 lagging (c) 0.7 leading

Jan-13

07

10

A 4 KVA, 3 phase, 110V, 50Hz, star connected alternator has Xd

= 3 ohm and Xq = 2 ohm. The machine is delivering full load

current of 0.8 p.f lagging at rated voltage. Find the induced emf,

load angle and maximum power output of the alternator.

May-13

07

11

In a 50 KVA , star connected, 440 V, 3 phase, 50 Hz alternator, the

effective armature resistance is 0.25 ohm per phase. The synchronous

reactance is 3.2 ohm per phase and leakage reactance is 0.5 ohm per

phase. Determine at rated load and unity power factor. (a) Internal

e.m.f. Ea, (b) no-load e.m.f. Eo. (c ) percentage regulation on full load

(d) value of synchronous reactance which replaces armature reaction.

Nov-13

07

12 A 100 kVA, 3000 V, 50 Hz, 3 phase star connected alternator has

effective armature resistance of 0.25 ohm. The field current of 400 A

produces short circuit current of 180A and an open circuit voltage of

May-15 07

1040 V (line value). Find the full load voltage regulation at 0.85 PF

lagging and 0.85 PF leading.

13

A 3-phase, 8-pole, 750 rpm star-connected alternator has 72

slots on the armature. Each slot has 12 conductors and

winding is short chorded by 2 slots. Find the induced emf

between lines, given the flux per pole is 0.06Wb.

May-11

07

Chapter-5 Synchronous motor: Methods of starting of synchronous motors, Different torques inSynchronous motor, Stability, Synchronous condenser, Synchronous phase modifiers, V-curves and O-curves of Synchronous motors. Auto Synchronous Motor: Construction, principle of operation, equivalent excitation current fordifferent rotor connections, circle diagrams.

ATTEMPT THREE THEORIES:

SR

NO. QUESTION YEAR MARKS

1

Explain an experimental method of determining ‘V’ curves for

a synchronous motor.

OR

Explain V and inverted V curves of synchronous motor

May-11

Jan-13

Nov-11

May-12

May-13

07

2 Discuss different torques in synchronous motor.

May-11 04

3

Explain the slip test for measurement of Xd and Xq of

synchronous machines. Draw circuit diagram.

Nov-11

Jan-13

Nov-13

07

4 Explain hunting of synchronous machines and methods of its

prevention.

Nov-11

Nov-13 07

5

Explain the effect of varying excitation at constant load on

synchronous motor.

OR

Explain the effect of varying excitation at constant load on

synchronousmotor.

Nov-11

May-13 07

6

Why synchronous motor is not self starting? Explain the

methods of starting of synchronous motor.

Nov-11

May-12

May-13

Nov-13

June-16

07

7 Derive the expression for the input and output power developed

by synchronous motor. Also derive the maximum input and

output power developed by synchronous motor.

May-12

May-13 07

ATTEMPT EXAMPLE:

SR

NO. QUESTION YEAR MARKS

1

A 3 phase, 6 poles, 2.3 KV, 200KVA, star connected

synchronous motor has synchronous reactance of 12 ohm per

phase and negligible resistance. The motor is initially

operating at a load of 120KW with the field current adjusted

such that the armature current is minimum. The field current

is now increased such that the armature current is increased

by 50%. With this field current, the load is reduced to 60KW.

Calculate the new values of armature current and power

factor.

Nov-11 07

Chapter-6 Commutator motors: Construction and working principle of Schrage motor, Universal motor and Repulsion motor

ATTEMPT THREETEORIES:

SRNO. QUESTION YEAR MARKS

1 Explain construction & working of Universal motor.

Dec-10

MAY-13 07

2

Discuss how the speed and power factor of a Schrage motor can be varied by an emf injected into its secondary winding. Compare the frequency of the emf induced and injected into secondary winding.

June-11 07

3

Why are the compensating windings and the interpole windings used in a universal motor for A.C operation? Draw the schematic connection diagram for all the stator windings and the armature for ac-operated series [universal] motor.

June-11 07

4

What is the role of commutator in an AC commutator motor? Explain the working of a Schrage motor.

Dec-11

Nov-14

May-15

June-16

07

5

Discuss the working of a) Repulsion motor b) Universal motor

OR Discuss working of Repulsion motor and Universal Motor.

Dec-11

May-15 07

6 Discuss constructional features, working and application of Schrage motor in detail.

June-12

MAY-13

June-14

07

7 Explain the construction and working principle of Repulsion motor.

June-14 07

ATTEMPT EXAMPLE:

SR

NO. QUESTION YEAR MARKS

1

An A.C. operated universal motor has a 2-pole armature with 960 conductors. At a certain load, the motor speed is 5000 rpm and the armature current is 4.6A; the armature terminal voltage and input are 100 V and 300 W respectively.

June-11

Nov-14 07

Calculate the following quantities assuming an armature resistance of 3.5 ohms:

a) Effective armature reactance. b) Maximum value of useful flux/pole.