Induction Motors Objectives Part 03

41. Which of the following is likely to be the full load power factor of a three-phase induction motor? 0.8 lagging.


42. No load power factor of a three-phase induction motor is expected to be closer to 0.2 Lagging.

43. Full load current of an induction motor is 20A. The no load current is expected to be 6A to 10A.


44. In terms of slip S, the ratio (Rotor Copper Loss / Rotor Output) = (S / (1-S)).


45 Which of the following methods can be used for the speed control of an induction motor? Pole Changing, Change of frequency and Cascade control.


46. In case the supply voltage and frequency of a 3-phase induction motor are reduced to half, the maximum torque will remain unchanged.


47. In order to run an induction motor on synchronous speed, e.m.f must be injected in the rotor in phase with rotor e.m.f.


48. The stator of 5 H.P induction motor is provided with semi-closed slots with parallel teeth.


49. For a 60HP motor, which type of rotor will be preferred? Wound rotor.


50. Two slip ring induction motors having number of poles as P1 and P2 respectively are connected in cascade. If the supply frequency is f, the speed of the main motor will be ๐Ÿ๐Ÿ๐ŸŽ๐’‡๐‘ท๐Ÿ+๐‘ท๐Ÿ.


51. A 3-phase induction motor is running on balanced supply. Suddenly one phase fuse blows off and the motor continues to operate. Such an operation of motor is known as single phasing.


52. If a squirrel cage induction motors runs too hot, the probable reason could be Uneven Air gap, low voltage, clogged ventilating ducts.


53. If a squirrel cage motor fails to start which of the following could not be the reason for the same? Uneven air gap.


54. If a 3-phasesquirrel cage motor runs slow, which could not be the reason for the same? High frequency.


55. Jogging of an induction motor is energizing a motor once or repeatedly to obtain small movements for mechanism.


56. Under which method of starting an induction motor is expected to take largest starting current direct On-Line starting.


57
. An induction motor will develop maximum torque when the phase difference between stator and rotor current is 60 Degree Electrical.


58. The condition for maximum torque of the rotor of an induction motor is slip should be such that rotor reactance per phase is equal to resistance per phase.


59. As the load on induction motor goes on increasing power factor goes on increasing up to rated load and then it starts falling.

60. Which motor has the highest power to weight ratio? Universal motor.