Synchronous Motors PART 4
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Attempt Free Synchronous Motors PART 4 Here. Read The Important Electrical MCQ From Below.
46. In a synchronous motor which loss does not vary with load ?
(A) Copper losses
(B) Hysteresis losses
(C) Windage losses
(D) None of the above.
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47. In a 3-phase. 400 V, 50 Hz salient pole synchronous motor, the maximum power is obtained when the load angle is
(A) 45°
(B) less than 90°
(C) 90°
(D) more than 90°.
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Synchronous Motors PART 4
48. A high starting torque synchronous motor has
(A) simplex rotor
(B) phase wound damper
(C) five slip rings
(D) all of the above.
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49. In a three phase synchronous motor, the magnitude of field flux
(A) varies with speed
(B) varies with load
(C) remains constant at all loads
(D) varies with power factor.
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50. The parameter connected with the operation of a synchronous motor are
I. Speed
II. Power factor
III. Armature current.
When the excitation of the motor is varied, which parameters vary along with it
(A) I only
(B) II only
(C) II and III only
(D) I, II and III.
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Synchronous Motors PART 4
51. A 3 phase, 400 V, 50 Hz salient pole synchronous motor is running on no load. If there is break in the excitation
winding of the motor
(A) the motor will stop
(B) the winding will get overheated
(C) the motor will run as reluctance motor at the rated rpm
(D) the motor will run as reluctance motor at lower rpm.
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52. In the figure shown with curve represents the variation of synchronous reactance for a synchronous motor with field current ?
(A) curve A
(B) curve B
(C) curve C
(D) curve D.
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53. A synchronous motor is said to be ‘floating’ when it operates
(A) on no load and without losses
(B) on constantly varying load
(C) on pulsating load
(D) on high load and variable supply voltage.
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Synchronous Motors PART 4
54. The negative phase sequences in a three phase synchronous motor exist when
(A) motor is overloaded
(B) motor is under loaded
(C) unbalanced voltage is supplied
(D) motor armature is hot.
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55. The field winding of a synchronous motor is shorted. A variable voltage is now supplied to the stator. The result will be
(A) stator winding will bum
(B) motor will not run
(C) motor will rotate at synchronous speed on light load
(D) motor will rotate at a speed which is less than the synchronous speed.
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56. In a three phase synchronous motor, the poles
(A) are along the resultant air-gap flux wave φ r
(B) arc opposite to φ r
(C) lag φ r
(D) lead φ r
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Synchronous Motors PART 4
57. A 3 phase synchronous motor is running clockwise. In case the direction of its field current is reversed
(A) the motor will continue to run in the same direction
(B) the motor will run in the reverse direction
(C) the motor will stop
(D) the winding of the motor will burn.
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(A) 5%
(B) 1%
(C) 0.4%
(D) zero.
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59. When E is the supply voltage and R is the rotor resistance per phase, the mechanical power develop by a synchronous motor per phase is given by
(A) V2R
(B) V2/2R
(C) V2/4R
(D) 2V/3R
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60. In a synchronous motor, the synchronizing power comes into action when
(A) rotor speed is equal to synchronous speed
(B) rotor speed is less than synchronous speed
(C) rotor speed is more than synchronous speed
(D) rotor speed is either less or more than synchronous speed.
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Synchronous Motors PART 4
