B.E EEE Nov Dec 2011 Question Paper: EE52 Electrical Machines - II Fifth Semester Anna University of Technology, Coimbatore

ANNA UNIVERSITY OF TECHNOLOGY, COIMBATORE

B.E./B.Tech. DEGREE EXAMINATION, November/December 2011

FIFTH SEMESTER - EEE

ELECTRICAL MACHINES II

Time : Three hours Maximum : 100 Marks

Answer ALL Questions

PART A - (10 X 2 = 20 Marks)

1. Why altemators are rated in kVA not in kW?

2. Why short pitch windings are preferred over full pitched winding?

3. What are the causes of changes in voltage of altemators when loaded?

4. What does hunting of synchronous motor mean?

5. Define slip of an induction motor.

6. What is induction generator?

7. Is it possible to add an external resistance in the rotor circuit of a cage induction motor? Justify your answer.

8. Mention the methods to change the speed of an induction motor.

9. Why the single‘phase induction motors are not self Starting one?

10. Mention the applications of stepper motor.

PART- B (5 X 16 = 80 MARKS)

11. a. Explain the construction and working principle of synchronous machines in detail (8)

b. The open circuit and short circuit test readings for a 3-phase star connected 1000 kVA, 2000V, 50 Hz synchronous generators are.....

EE52 Electrical Machines - II Fifth Semester Anna University of Technology, Tirunelveli, B.E EEE Nov Dec 2011 Question Paper

ANNA UNIVERSITY OF TECHNOLOGY, TIRUNELVELI

B.E./B.TECH. DEGREE EXAMINATION, November/December 2011

FIFTH SEMESTER - EEE

ELECTRICAL MACHINES 11

Time : Three hours MaXimum i 100 Marks

Answer ALL Questions

PART A - (10 X 2 = 20 Marks)

1. What do you mean by synchronous reactance?

2. What is the purpose of conducting slip test?

3. Is synchronous motor inherently self-starting or not.

4. State any two methods of starting synchronous motor.

5. What are the losses produced in induction motor?

6. Write down the equation for running torque of an induction motor.

7. Why induction motor draws large current from the supply during starting?

8. How many speeds you can obtain by cascaded connection of induction motors?

9. Why is the single phase induction motor having two winding in this stator?

10. State any two applications capacitor start run induction motor.

PART-B (5 X 16 = 80 MARKS)

11. a. 1) Explain the effects of armature reaction for different power factor loads. (8)

Question Paper of EE52 Electrical Machines - II Fifth Semester Anna University Trichy, B.E EEE November December 2011

ANNA UNIVERSITY OF TECHNOLOGY, TRICHY

B.E./B.TECH. DEGREE EXAMINATION, November/December 2011

FIFTH SEMESTER - EEE

ELECTRICAL MACHINES II

Time : Three hours    Maximum : 100 Marks

Answer ALL Questions

PART A - (10 X 2 = 20 Marks)

1. Define distribution factor.

2. What is damper winding? Why is it used?

3. Why does the synchronous motor develop torque only at synchronous speed?

4. What is a phase advancer?

5. Why three phase induction motor called singly excited motor?

6. Define slip.

7. How can speed of three phase induction motor be controlled?

8. What is induction generator?

9. Define step angle.

10. How will you change the direction of rotation of a split phase induction motor?

PART B - (5 x  16 = 80 MARKS)

11. a. Explain in detail MMF method of predetermining the voltage regulation of the alternator. (8)

b. A 4 -pole 3 phase, 50 Hz star connected alternator has 60 slots, with four conductors per slot. Coils are short pitched by three slots. If the phase spread is 60°, find the line induced voltage for a flux per pole of 0.943 Wb distributed sinusoidally in space. All the turns per phase are in series. (8)

or

12. a. Derive the expression for synchronizing current, power and torque. (10)

b, Calculate the maximum load on a 5 MVA, three phase alternator having a synchronous reactance of 5 ohm can deliver when connected to 6.6 kV bus bar if its excitation is such that the emf on open circuit is 6 kV. Find the armature current and power factor at this load. (6)

13. a. Derive an expression for power developed in a synchronous motor. (8)

b, A 3300 V, 1.5 MW, 3-phase Y connected synchronous motor has X d = 4 ohm per phase and Xq = 3 ohm per phase. Neglecting all losses, calculate the excitation EMF. When motor supplies rated load at unity PF. Calculate the maximum mechanical power would develop for this field excitation. (8)

EE52 Electrical Machines - II Anna University Chennai, Fifth Semester B.E EEE May June 2012 Question Paper

Anna University Chennai, EE52 Electrical Machines - II Fifth Semester B.E EEE May June 2012 Question Paper

ANNA UNIVERSITY

B.E.IB.TECH. DEGREE EXAMINATION, May/June 2012

FIFTH SEMESTER - EEE

ELECTRICAL MACHINES II

Time : Three hours   Maximum 100 Marks

Answer ALL Questions

PART A - (10 X 2 = 20 Marks)

1. Why is the field system of an alternator made as a rotor?

2. What is synchronizing power of an alternator?

3. What is hunting?

4. Why a synchronous motor is a constant speed motor?

5. How the direction of rotation of a three-phase induction motor can be reversed?

6. What is an induction generator?

7. Why starter is necessary for the induction motor?

8. Why most of the 3-phase induction motors constructed with delta are connected stator winding?

9. What is the advantage of capacitor start induction motor over split-phase induction motor?

10. Why centrifugal switches are provided in many l-phase induction motors?

PART - B (5 x 16 = 80 Marks)

11. a. 1) Explain the phenomena of armature reaction in alternator for different load power factors. (6)

ii) Explain clearly the ZPF method of determining the regulation of an alternator? (10)

Anna University Chennai, EE52 Electrical Machines - II Fifth Semester B.E EEE May June 2011 Question Paper

Anna University Chennai

B.E/B.Tech Degree Examinations May / June 2011

Regulations 2008

Fifth Semester - BEE

EE52 - Electrical Machines - II

Electrical and Electronics Engineering

Time : 3 hours  Max. Marks : 100

Part-A (10 x 2=20 marks)

Answer all Questions

1. What are the effects of Armature reactor?

2. State the condition for parallel operations of Alternator.

3. List any two characteristic features of synchronous motor.

4. What is the synchronous condenser?

5. ‘Why is the Induction motor always runs with the speed less than the synchronous speed?

6. Define slip.

7. What is the need for starters in Induction motor?

8. What are the speed control techniques applicable to squirrel cage induction motor?

9. Define double field revolving theory.

10. Write down any two applications of single phase induction motors.

Part B (5 x 16 = 80)

11. a) i. Derive the emf equation of Alternator.  (8)

ii. A motor generator set used for providing variable frequency a.c. supply consists of a three-phase, 10-pole synchronous motor and a 24-pole, three phase synchronous generator. The motor-generator set is fed from a 25 Hz three phase a.c. supply. A 6-pole, three phase induction motor is electrically

connected to the terminals of the synchronous generator and runs at a slip of 5%. Determine:

The frequency of the generated voltage of the synchronous generator.

The speed at Which the induction motor is running. (8)

Remaining questions can be collected from the images provided below.