# ONLINE Multiple Choice Questions EE-Synchronous Motors PART 4

46. In a synchronous motor which loss does not
(A) Copper losses
(B) Hysteresis
losses
(C) Windage
losses
(D) None
of the above.

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°.

48. A high starting torque synchronous motor has
(A) simplex
rotor
(B) phase
wound damper
(C) five
slip rings
(D) all
of the above.

49. In a three phase synchronous motor, the
magnitude of field flux
(A) varies
with speed
(B) varies
(C) remains
(D) varies
with power factor.

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.

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.

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.

53. A synchronous motor is said to be ‘floating’ when it operates
(A) on
(B) on
(C) on
(D) on
high load and variable supply voltage.

54. The negative phase sequences in a three phase synchronous motor
exist when
(A) motor
(B) motor
(C) unbalanced
voltage is supplied
(D) motor
armature is hot.

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.

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

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.

58. The speed regulation of a 3 phase synchronous motor is

(A) 5%
(B) 1%
(C) 0.4%
(D) zero.

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