B.E- 3rd Sem (Anna University of Technology Tirunelveli -2012)
Sunday, 07 July 2013 12:49Jeya Priya
Third Semester
EE1202- ELECTRICAL MACHINES-I
(Regulation 2004)
(common to B.E. (Part-Time) Second Semester Regulation 2005)
Answer All questions
PART-A (10*2=20 marks)
1. What is the single and multiple excited system?
2. What is meant by distributed winding?
3. Define armature reaction?
4. What are the advantages of parallel operations?
5. What is the significance of back emf in a DC motor?
6. Why is DC series motor called variable speed motor?
7. What are the losses in a transformer? and how will you minimize those losses?
8. Discuss why auto transformers cannot be used as distribution transformers.
9. State the merits and demerits of Swinburnes test?
10. What is the use of polarity test on transformers?
PART-B (5*16=80 marks)
11. (a) Explain clearly the principle of electromechanical energy conversion with neat diagrams.(16)
or
(b) Deduce an expression for torque in round rotor motor.(16)
12. (a)
(i) Derive an expression for the emf of DC generator. (8)
(ii) A 6-pole DC generator has 150 slots. Each slot has 8 conductors and each conductor has
resistance of 0.01 ohm. The armature terminal current is 15A. Calculate the current per
conductor and the drop in armature for lap and wave winding connections.(8)
or
(b) Writes note on the following:
(i) Self and separately excited DC generators. (8)
(ii) Commutation. (8)
13. (a) Explain the different methods of excitation and characteristics of a DC motors with suitable
diagrams. (16)
or
(b)
(i) What is the necessity of starters? and with neat sketch explain functions of the 3-point
starter in detail. (10)
(ii) A 200V DC series motor runs at 500rpm when taking a line current of 25A. The resistance of
the armature and field windings are 0.3 ohm and 0.5 ohm respectively. If the current taken
remains constant, calculate the resistance necessary to reduce the speed to 350rpm.(6)
14. (a) Explain with vector diagrams of a transformer on no load and load with upf, lagging and
leading power factors. (16)
or
(b) Write notes on the following:
(i) Auto transformers.(8)
0
(ii) Three phase transformers. (8)
15. (a)
(i) Obtain the condition for maximum efficiency of the DC generator.(8)
(ii) A 400V DC shunt generator has a full load current of 200A. The resistance of the armature
and the field windings are 0.06 ohm and 100 ohm respectively. The stray losses are 2000W.
Find the KW output of prime mover when it is delivering full load and find the load for
which the efficiency of the generator is maximum. (8)
OR
(b) With neat diagram explain the method of calculating the regulation and efficency of a single
phase transformer by open and short circuit tests. Also state its merits and demerits. (16)
| Earning: ₹ 5.10/- |
