31. The interaction torque in a synchronous motor depends upon
- stator field strength alone
- rotor field strength alone
- torque angle alone
- all of the above
32. The breakdown torque of a synchronous motor varies as
- applied voltage V
- V²
- 1/V
- 1/V²
33. Higher the applied voltage
- higher will be the stator flux
- higher will be the pull-in torque
- lower will be the stator flux
- lower will be pull-in torque
- both (1) and (2)
- both (1) and (4)
34. The operation of a 3-phase synchronous motor operating on constant excitation across infinite bus will not be stable if power angle δ
- exceeds internal angle θ
- is less than θ
- exceeds θ/2
- is less than θ/2
35. A synchronous motor is supplying load at unity power factor. If the load on the motor is increased keeping its excitation and terminal voltage constant, the power factor
- will remain the same.
- will become leading.
- will become lagging.
- none of the above.
36. When does a synchronous motor operate with leading power factor current?
- While it is underexcited
- While it is critically excited
- While it is overexcited
- While it is heavily loaded
37. A three phase synchronous motor connected to ac mains is running at full load and unity power factor. If its shaft load is reduced by half, with field current held constant, its new power factor will be
- unity
- leading
- lagging
- dependent on machine parameters
38. A 3-phase synchronous motor connected to an infinite bus is operating at half-full load with normal excitation. When the load on the synchronous motor is suddenly increased
- its speed will first decrease and then become synchronous
- its speed will first increase and then become synchronous
- its speed will fluctuate around synchronous speed and then become synchronous
- its speed will remain unchanged
39. A synchronous generator connected to an infinite bus is over excited. Considering only the reactive power, from the point of view of the system, the machine act as
- capacitor
- inductor
- resistor
- none of the above
40. A synchronous machine connected to a power system grid bus bar is operating as a generator. To make the machine operate as a motor, the
- direction of rotation is to be reversed.
- phase-sequence is to be changed.
- field excitation is to be decreased.
- mechanical input is to be less than the losses at the shaft.