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Electrical Engineering Objective Questions { Synchronous Motors }

29. If one of the 3-phases of a synchronous motor is short circuited, the motor will
A. start
B. not start
C. get overheated
D. fail to pull into synchronous

30. The merit of synchronous motor over induction motor is that
A. it runs at a constant speed
B. it can run over a wide range of power factors both lagging and leading
C. its torque is less sensitive to change in supply frequency
D. all of these

31. Speed of synchronous motor depends upon
A. number of poles
B. supply frequency
C. both (a) and (b) above
D. none (a) nor (b) above

32. Synchronous motors are not self starting because
A. stator is not used
B. starting winding is not provided
C. there is no slip
D. the direction of instantaeous torque on the rotor reverse after half cycle

33. A synchronous motor always runs at synchronous speed because of
A. Lenz's law
B. magnetic locking between the stator and rotor
C. the action of amortisseur winding
D. Faraday's law of electromagnetic induction

34. Statement : The magnitude of stator back emf depends on I. load II. Speed III. DC excitation Combinations
A. I only
B. 1 and II only
C. H and III only
D.1, II and III

35. Statement : Hunting is a sychronous motor can be used by I. variable load II. variable frequency III. variable supply voltage IV. windage friction Combinations
A. I, II and III
B. II, III and IV
C. HI, IV and I
D. IV, land II

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