Objective Questions on Alternators | Part 3

31. In order to reduce the harmonics in the emf generated in an alternator

(A) slots are skewed
(B) salient pole tips are chamfered
(C) winding is well distributed
(D) all of the above.

32. The maximum power in a synchronous machine is obtained when the load angle is

(A) 0°
(B) 85°
(C) 120°
(D) 135°.

33. The emf generated due to nth harmonic component of flux in an alternator will be

(A) n times the fundamental emf
(B) same as fundamental emf
(C) less than the value of fundamental emf.

34. Synchronizing torque comes into operation under all of the following cases EXCEPT

(A) phase difference between two voltages
(B) frequency difference between two voltages
(C) voltage difference between two voltages
(D) reduction in exciting current in one of the alternators.

35. Unbalanced 3-phase stator currents cause

(A) double frequency currents in the rotor
(B) healing of rotor
(C) vibrations
(D) all of the above.

36. In large generators protection provided against external faults is

(A) biased differential protection
(B) sensitive earth fault protection
(C) inter-turn fault protection
(D) all of the above.

37. Pitch factor is the ratio of the emfs of

(A) short pitch coil to full pitch coil
(B) full pitch winding to concentrated winding
(C) full pitch winding to short pitch winding
(D) distributed winding to full pitch winding.

38. In an alternator if the winding is short pitched by 50 electrical degrees, its pitch factor will be

(A) 1.0
(B) 0.866
(C) 0.75
(D) 0.50.

39. The Potier’s triangle separates

(A) stator losses and rotor losses
(B) fixed losses and variable losses
(C) armature voltage and field voltage
(D) armature leakage reactance and armature reaction mmf.

40. If a single phase alternator has 8 slots per pole uniformly speed, but the winding is arranged with the middle two left empty, the breadth coefficient will be

(A) 0.99
(B) 0.88
(C) 0.67
(D) 0.53.

41. Two alternators are running in parallel. If the field of one of the alternator is adjusted, it will

(A) reduce its speed
(B) change its load
(C) change its power factor
(D) change its frequency.

42. A generator is operating by itself supplying the system loads. The reactive power supplied by the generator will

(A) depend on prime mover rpm
(B) depend on type of insulation used
(C) depend on the amount demanded by the load
(D) depend on inter-coil inductance.

43. Which of the following part plays important role in over speed protection of a generator ?

(A) Over current relay
(B) Alarm
(C) Differential protection
(D) Governor.

44. Which type of protection is provided on a generator to protect against stator insulation failure ?

(A) Differential protection
(B) Thermocouple actuated alarm
(C) Over current relay
(D) Reverse power relay.

45. Which relays comes into operation in the event of the failure of prime mover connected to ihe generator ?

(A) Reverse power relay
(B) Differential relay
(C) Buchholz relay
(D) None of the above.

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