Synchronous motors

41. The magnitude of field flux in a 3-phase synchronous motor

remains constant at all loads
varies with speed
varies with the load
varies with power factor

Detailed SolutionThe magnitude of field flux in a 3-phase synchronous motor

42. If the field winding of an unloaded salient pole synchronous motor is open circuited, the motor will

stop
run as induction motor
function as static condenser
burn with dense smoke

Detailed SolutionIf the field winding of an unloaded salient pole synchronous motor is open circuited, the motor will

43. A synchronous motor is running on a load with normal excitation. Now if the load on the motor is increased

power factor as well as armature current will decrease
power factor as well as armature current will increase
power factor will increase but armature current will decrease
power factor will decrease and armature current will increase

Detailed SolutionA synchronous motor is running on a load with normal excitation. Now if the load on the motor is increased

44. A synchronous motor running with normal excitation adjusts to load increases essentially by increase in

back e.m.f.
armature current
power factor
torque angle

Detailed SolutionA synchronous motor running with normal excitation adjusts to load increases essentially by increase in

45. Stability of a synchronous machine

decreases with increase in its excitation
increases with increase in its excitation
remains unaffected with increase in excitation
any of the above

Detailed SolutionStability of a synchronous machine

46. The effect of increasing the load on a synchronous motor running with normal excitation is to

decrease both armature current and power factor
decrease armature current but increase power factor
increase armature current but decrease power factor
increase both its armature current and power factor

Detailed SolutionThe effect of increasing the load on a synchronous motor running with normal excitation is to

47. The net armature voltage of a synchronous motor is equal to the

vector sum of Eb and V
arithmetic sum of Eb and V
arithmetic difference of Eb and V
vector difference of Eh and V

Detailed SolutionThe net armature voltage of a synchronous motor is equal to the

48. In a synchronous motor, the magnitude of stator back e.m.f. (Eb) depends on

d.c. excitation only
speed of the motor
load on the motor
both the speed and rotor flux

Detailed SolutionIn a synchronous motor, the magnitude of stator back e.m.f. (Eb) depends on

49. Change of D.C. excitation of a synchronous motor changes

Applied voltage of the motor
Motor speed
excitation of a synchronous motor changes A. Applied voltage of the motor B. Motor speed C. Power factor of power drawn by the motor
Any of the above

Detailed SolutionChange of D.C. excitation of a synchronous motor changes

50. A synchronous motor can be used as a synchronous capacitor when it is

under-loaded
over-loaded
under-excited
over-excited

Detailed SolutionA synchronous motor can be used as a synchronous capacitor when it is

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