3-PHASE INDUCTION MOTOR - 6 | Take the Quiz

51. Each of the following statements regarding stator flux of an induction motor is true except _________

it induces e.m.f. in the rotor bars

its magnitude depends on the motor load

it is constant in magnitude

it revolves around the stator at synchronous speed

52. When a load on a squirrel-cage induction motor is increased from no-load to full-load, which of the following statement is incorrect?

slip increases

the magnetizing component of the stator exiting current is increased

stator power factor is improved

torque developed by the motor increases till it equals the applied torque

53. The principle of operation of a 3-phase induction motor is most similar to that of ____

transformer with a shorted secondary

synchronous motor

capacitor-start induction run motor

repulsion-start induction motor

54. A squirrel cage induction motor running on no-load is loaded, which of the following statements is incorrect?

current in the rotor bars decreases

motor speed decreases

torque developed by the rotor increases

stator flux cuts the rotor bars more rapidly

55. When a double squirrel cage motor is started, the current induced in the rotor _____

flows mostly through the upper winding

flows mostly through the lower winding

is directly proportional to the impedance offered by the each cage

is equally divided between the two windings

56. Regarding single-phasing of a 3-phase induction motor under running conditions which of the following statements is incorrect?

it will stop and blow the remaining fuses

it will continue to run without damage if it is carrying half load or less

it will stop and promptly burnt out if it is heavily overloaded

it will try to keep running though over-heating of part of its winding if it is carrying full-load or slight overload

57. If ‘s’ is the slip and ‘f’ is the supply frequency, the frequency of rotor current is given by _________

s.f

s2f

s.f⁄2

f⁄s

58. Which of the following statements is correct about an induction motor?

it is self starting with high torque

it is self starting with zero torque

it is self starting with small torque as compared to rated torque

none of the above

59. Type of bearing used for 25 H.P. motor is ___________

roller bearing

bush bearing

needle bearing

ball bearing

60. When an induction motor is switched on, the rotor frequency is ___________

zero

60 HZ

same as slip frequency

same as supply frequency