Induction Motors Objectives Part 02

21. The power output of an induction motor will be minimum when the equivalent resistance is equal to the stand leakage impedance of the motor.

22. The ‘injected e.m.f’ in the rotor of induction motor must have same frequency as the slip frequency.

23. The running speed of a three-phase induction motor is synchronous speed * (1-slip).

24. Commonly used ac motor for industrial applications is 3-phaseinduction motor.

25. Abrasive, dust and dirt is best removed from an induction motor by Vacuum suction.

26. When the rotor of an induction motor is standstill, the value of slip is 1.0.

27. In a squirrel cage induction motor, rotor induced e.m.f at standstill varies as stator flux.

28. A wound rotor induction motor can be distinguished from squirrel cage induction motor by presence of slip rings.

29. Motors for fans and pumps are selected in the rpm range 1440 to 2880.

30. The class of insulation generally not provided on electric motor is Class F.

31. An induction motor is said to be crawling when it runs at 10 to 15 percent of rated speed.

32. Direct on-line starting current as compared with star delta starting current is approximately 3 times.

33. The efficiency of induction motor is expected to be in the range 80 to 90 percent.

34. The value of flux density in the air gap is usually in the range of 0.35 to 0.6 Wb/m2.

35. The speed load characteristics of an induction motor resembles which of the following motor DC Shunt Motor.

36. In an induction motor, if the flux density of rotor is reduced to half of its normal value, the torque will be reduced to half.

37. Negative sequence currents are set up in an induction motor when unbalanced 3-phase supply is given.

38. Unbalanced 3-phasevoltage supply to an induction motor results in excessive heating of rotor.

39. The torque of a three-phase induction motor is proportional to square of applied voltage.

40. Which of the following will improve in case air gap length of a three-phase induction motor is reduced power factor.