Single Phase Induction Motors

21. If a particular application needs high speed and high starting torque, then which of the following motor will be preferred?

  1. Universal motor
  2. Shaded pole type motor
  3. Capacitor start motor
  4. Capacitor start and run motor

Correct answer: (A)
Universal motor

22. If a single phase induction motor runs slower than normal, the most likely defect is

  1. worn bearings
  2. short-circuit in the winding
  3. open-circuit in the winding
  4. none of the above

Correct answer: (A)
worn bearings

23. If starting winding of a single-phase induction motor is left in the circuit, it will

  1. run faster
  2. spark at light loads
  3. draw excessive current and overheat
  4. run slower

Correct answer: (C)
draw excessive current and overheat

24. If the capacitor of a single-phase motor is short-circuited

  1. the motor will not start
  2. the motor will run
  3. the motor will run in reverse direction
  4. the motor will run in the same direction at reduced r.p.m.

Correct answer: (A)
the motor will not start

25. If the centrifugal switch does not open at 70 to 80 percent of synchronous speed of motor, it would result in

  1. damage to the starting winding
  2. damage to the centrifugal switch
  3. overloading of running winding
  4. none of the above

Correct answer: (A)
damage to the starting winding

26. If the centrifugal switch of a two-value capacitor motor using two capacitors fails to open then

  1. motor will not come up to speed
  2. motor will not carry the load
  3. current drawn by the motor will be excessively high
  4. electrolytic capacitor will, in all probability, suffer break down

Correct answer: (D)
electrolytic capacitor will, in all probability, suffer break down

27. In a A.C. series motor armature coils are usually connected to commutator

  1. through resistance
  2. through reactances
  3. through capacitors
  4. solidly

Correct answer: (A)
through resistance

28. In a capacitor start and run motors the function of the running capacitor in series with the auxiliary winding is to

  1. improve power factor
  2. increase overload capacity
  3. reduce fluctuations in torque
  4. to improve torque

Correct answer: (A)
improve power factor

29. In a capacitor start motor, the phase displacement between starting and running winding can be nearly

  1. 10°
  2. 30°
  3. 60°
  4. 90°

Correct answer: (D)
90°

30. In a capacitor start single-phase motor, when capacitor is replaced by a resistance

  1. torque will increase
  2. the motor will consume less power
  3. motor will run in reverse direction
  4. motor will continue to run in same direction

Correct answer: (D)
motor will continue to run in same direction

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