51. In a synchronous motor, the excitation voltage on no load is approximately equal to the applied voltage. This will happen
- the torque generated is maximum
- the excitation is said to be zero
- the excitation is said to be 100%
- the motor is said to be fully loaded
52. Which motor can conveniently operate at lagging as well as leading power factor?
- squirrel cage induction motor
- wound rotor induction motor
- synchronous motor
- DC shunt motor
53. At constant load, the magnitude of armature current drawn by a synchronous motor is large for
- low excitation.
- high excitation.
- both low and high values of field excitation.
- 100% excitation
54. Variation in dc excitation of a synchronous motor causes variation in
- speed of motor
- power factor
- armature current
- both armature current and power factor
55. If the field of a synchronous motor is under excited, the power factor will be
- lagging
- leading
- unity
- more than unity
56. A synchronous motor installed at the end of transmission line is operating at lagging power factor. With the fall in supply voltage, the power factor of the synchronous motor will
- go down
- improve
- remain unchanged
- none of these
57. A 3-phase salient pole synchronous motor is connected to the infinite bus. It is operated at no load at normal excitation. The field excitation of the motor is first reduced to zero and then increased in the reverse direction gradually. Then the armature current
- increases continuously
- first increases and then decreases steeply
- first decreases and then increases steeply
- remains constant
58. A synchronous motor is operating on no load at unity power factor. If the field current is increased, the power factor will become
- leading and the current will decrease
- lagging and the current will increase
- lagging and the current will decrease
- leading and the current will increase.
59. A 3-phase synchronous motor is operating at a given load. If an increase in excitation reduces the armature current, it can be concluded that the motor is
- operating at lagging power factor and absorbing reactive power from the mains
- operating at leading power factor and delivering reactive power to the mains
- either (1) or (2)
- none of these
60. Stability of a synchronous motor _______ with the increase in excitation.
- increases
- decreases
- remains unaffected
- oscillates