EE6504 ELECTRICAL MACHINES-II, Third year, Department of Electrical and Electronics Engineering, Model Exam Questions.

ANSWER ALL THE QUESTIONS
PART A(10*2=20)
 1. Why a 3-phase synchronous motor will always run at synchronous speed?
2. What are the advantages of salient pole type of construction use for synchronous
      Machines?
3. What is meant by synchronous condenser?
4. What is meant by hunting of synchronous motor?
5. Why are slots on the cage rotor of induction motor usually skewed?
6. Define slip of an induction motor?
7. What are different methods of speed control employed in three phase cage induction motor?

8. Why starter is necessary for three phase induction motor?
9. What is the advantages of capacitor start induction motor over split phase induction motor?
10.Mention the application of hysteresis motor.

PART B(5*16=80)
11(a).Explain briefly the construction and working principle of alternator with neat sketch     (16)
                                                                       (OR)
(b). (i).Derive an EMF equation of an alternator                                                                          (8)
      (ii).A 2000 KVA,11KV, 3 phase star connected alternator has a resistance of 0.3Ω and reactance of 5Ω/ phase. It delivers full load current at 0.8 lagging power factor at rated voltage.
Compute the terminal voltage for the same excitation and load current at 0.8 power factor leading.                                                                                                                                          (8)
12 (a).Describe various method of starting of synchronous motor.                                          (16)
                                                                        (OR)
  (b). A 3 Phase, 11000V, star connected synchronous motor takes a load of 100A. The effective synchronous reactance and resistance per phase are 30Ω and 0.8Ω respectively. Find the power supplied to the motor and induced emf for (i). 0.8 pf lag, (ii). 0.8 pf lead.                                (16)
13.(a). A 3 phase ,6 pole  50 Hz induction motor has a slip of 1% at no load and 3% at full load. Find (1).synchronous speed (2).no load speed (3). Full load speed (4).frequency of rotor current at stand still (5).frequency of rotor current at full load.  (16)
                                                                        (OR)
 (b).(i). Draw and explain slip torque characteristics of 3 phase induction motor                      (8)
       (ii). Derive the torque equation of 3 phase induction motor.                                               (8)
14. (a)With neat sketch explain the two type of starters used for 3 phase squirrel cage inductance                   
motor                                                                                                                              (16)
                                                                          (OR)
       (b). Explain slip power recovery scheme.                                                                          (16)
15. (a).Explain briefly the operation of capacitor start and split phase induction motor.          (16)
                                                                           (OR)
      (b). Discuss briefly the operation and characteristics of
             (i). Repulsion motor
             (ii). AC series motor