Third Semester
Electronics and Communication Engineering
(Regulation 2008)
Time : Three hours Maximum : 100 Marks
Answer ALL questions
PART A — (10 × 2 = 20 Marks)

1. What is a dc compound generator?
2. What is the need for starter in dc motor?
3. Why is the core of transformer laminated?
4. Define voltage regulation of a transformer.
5. What are the types of 3-ph induction motors?
6. Name the starting methods for cage motors.
7. Why should an alternator run always at synchronous speed?
8. Write down the emf equation of alternator.
9. What are the various stages of an electric power system?
10. Mention the disadvantages of HVDC transmission.

PART B — (5 × 16 = 80 Marks)

11. (a) (i) Briefly explain the construction of a DC machine with neat diagram. (Marks 10)
(ii) A dc shunt generator has a terminal voltage of 160 V and a no-load induced emf of 168 V. The resistances of armature and field are 0.03 and 20 . Find the armature current, field current and load current. Neglect armature reaction. (Marks 6)
(b) (i) Explain the characteristics of series, shunt and compound motors.(9)
(ii) Explain the Ward Leonard method of speed control of dc shunt motor. (Marks 7)

12. (a) (i) Derive the emf equation of a transformer. (Marks 10)
(ii) A single phase transformer is rated at 240/120 V, 50 Hz, Find voltage and frequency of secondary at no-load (1) if primary voltage is 120 V, 25 Hz and (2) if primary voltage is 240 V dc. (Marks 6)
(b) (i) Deduce the equivalent circuit of 1-ph transformer. (Marks 6)
     (ii) A 1-ph transformer is rated at 10 KVA, 50 Hz. The secondary rated voltage is 240 V and the turns ratio is 10. The resistance and leakage reactant as referred to primary are 8.4 and 13.7 respectively. Find voltage regulation at full-load and power factors of 0.8 lagging, 0.8 leading and unity. (Marks 10)

13. (a) (i) Explain the principle of operation of 3-ph induction motor and (Marks 5)
(ii) A 3-ph, 6 pole 50 Hz cage motor is running with a slip of 4%. Find speed of the rotating field relative to the stator winding, motor speed and frequency of emf induced in the rotor. (Marks 6)
(iii) Briefly explain the starting of squirrel cage motor using star-delta starter. (Marks 5)
(b) Discuss the operation of following types of 1-ph induction motors with neat circuit diagrams and speed-torque characteristics.
(i) Capacitor-start, capacitor-run motor (Marks 8)
(ii) Shaded pole motor. (Marks 8)

14. (a) Briefly discuss the construction of the following :
(i) Stator of synchronous machine (Marks 8)
(ii) Salient pole and cylindrical rotors. (Marks 8)
(b) Explain the construction and operation of the following :
(i) Reluctance motor (Marks 8)
(ii) Hysteresis motor. (Marks 8)

15. (a) (i) Draw the one-line diagram of a typical power supply system. Mark all the components. (Marks 10)
(ii) What are the advantages of dc transmission systems over ac transmission systems? Explain. (Marks 6)
(b) (i) What are the main components used in transmission and distribution systems? Write down the functions of each. (Marks 8)
(ii) Compare overhead lines and underground cable systems. (Marks 8)