Shaded Pole Motor MCQ (Multiple Choice Questions) :: Single Phase Induction Motor

1. For a shaded pole induction motor, the direction of rotation of the motor is

  1. From the main pole to the shaded pole
  2. From the shaded pole to the main pole
  3. Either (A) or (B) depending on the voltage
  4. Either (A) or (B) depending on the power factor

Answer.1. From the main pole to the shaded pole

Explanation: The shaded pole motor rotates only in one particular direction, and the reverse movement of the motor is not possible The direction of rotation of the magnetic field is from the main (unshaded) pole to the shaded pole.

2. Shade pole motor is the category of ______

  1. DC motor
  2. Compound Motor
  3. Induction Motor
  4. Any of the above

Answer.3. Induction Motor

Explanation: Shaded pole motors are induction motors manufactured for very small ratings and are used in applications where starting torque requirement of the load is very low.

3. The stator of shaded pole motor is constructed with

  1. Salient Pole type
  2. Non-salient pole type
  3. Both 1 & 2
  4. None of the above

Answer.1. Salient Pole type

Explanation: Shaded pole motor is constructed with salient poles in stator. Each pole has its own exciting winding. In salient pole type of rotor consist of large number of projected poles (salient poles) mounted on a magnetic wheel. Salient pole rotors have large diameter and shorter axial length. They are generally used in lower speed electrical machines, say 100 RPM to 1500 RPM.

4. Shaded pole induction motor is usually ________ in efficiency, and built ________ HP

  1. Low, around 1/20 to 1/2
  2. Low, around 1
  3. High, around 2
  4. High, around 1

Answer.1. Low, around 1/20 to 1/2

Explanation: Shaded-pole motors are best suited to the low-power household application, because the motors have low starting torque and efficiency ratings. Because of the weak starting torque, shaded-pole motors are built only in small sizes ranging from 1/20 to 1/6 hp.

5. How much portion of the pole is cover with shading coil or shading band in shaded pole motor

  1. 1/2
  2. 1/4
  3. 1
  4. 1/3

Answer.4.

Explanation: A 1/3rd portion of each pole core is surrounded by a copper strip forming a closed loop called the shading band. When single phase AC supply is applied to the stator winding, due to shading coil provided to the poles, a rotating magnetic field is generated.

6. Rotor of shaded pole motor is similar to the construction of

  1. Split Phase Motor
  2. Synchronous Motor
  3. Squirrel cage motor
  4. DC motor

Answer.3. Squirrel cage motor

Explanation: The rotor of shaded pole induction motors is the Squirrel Cage type rotor. The rotor bars are provided with a 60-degree skew. This is to obtain an optimum starting torque and for limiting the torque dip during the run-up. Airgap length between stator and rotor is of the order 0.25 to 0.5 mm.

7. Shaded pole motors are built commercially with the capacity of _______

  1. 3 W to 125 W
  2. 5 kW and above
  3. 1 kW to 5 kW
  4. 500 to 1 kW

Answer.1. 3 W to 125 W

Explanation: Shaded pole motors are small in size and built commercially with the capacity of 3 W to 125 W. They are suitable for small devices like relays and fans because of their low cost and easy starting.

8. Each of the following statements regarding a shaded pole motor is true EXCEPT

  1. Its direction of rotation is from un-shaded to shaded portion of the poles
  2. It has high starting torque
  3. It has very poor power factor
  4. None of these

Answer.2. It has high starting torque

Explanation: The starting torque of shaded pole motor is very small about 50% of full load torque. The amount of torque produced is determined by the strength of the magnetic field of the stator, the strength of the magnetic field of the rotor, and the phase angle difference between rotor and stator flux. The shaded- pole induction motor has low starting and running torque.

9. The direction of rotation of shaded pole motor can be reversed by reversing the

  1. Supply terminal
  2. Changing shading coil position
  3. Changing the rotor position with respect to shading coil
  4. Position can’t be reversed

Answer.4. Position can’t be reversed

Explanation: The direction of rotation depends upon the position of the shading coil, i.e., which portion of the pole is wrapped with shading coil. The direction of rotation is from unshaded portion of the pole to the shaded portion. Its direction of rotation cannot be reversed unless the position of the poles is reversed. This is not a common practice, however. As a general rule the shaded-pole induction motor is considered to be nonreversible.

10. Which of the following motor has lowest starting torque?

  1. Reluctance Motor
  2. Shaded Pole Motor
  3. Repulsion Motor
  4. Universal Motor

Answer.2. Shaded Pole Motor

Explanation: The shaded-pole motor has the lowest starting torque of all the motor types. The starting torque of shaded pole motor is very small about 50% of full load torque. The amount of torque produced is determined by the strength of the magnetic field of the stator, the strength of the magnetic field of the rotor, and the phase angle difference between rotor and stator flux. The shaded- pole induction motor has low starting and running torque.

11. The copper ring in the shaded pole motor is also called

  1. Split Ring
  2. Stator coil
  3. Shading coil
  4. Rotor coil

Answer.3. Shading coil.

Explanation: A Shaded Pole motor is an AC single phase induction motor. The auxiliary winding, which is composed of a copper ring, is called a shading coil. The shading coil is wound around one end of the pole piece. It is actually a large loop of copper wire or a copper band. The two ends are connected to form a complete circuit. The shading coil acts like a transformer with a shorted secondary winding.

12. Which of the following motor does not have centrifugal switch?

  1. Capacitor start Motor
  2. Capacitor Run Motor
  3. Split phase Motor
  4. Shaded Pole Motor

Answer.4. Shaded Pole Motor

Explanation: The shaded-pole induction motor is popular because of its simplicity and long life. This motor contains no start windings or centrifugal switch. It contains a squirrel-cage rotor and operates on the principle of a rotating magnetic field created by a shading coil wound on one side of each pole piece. Shaded-pole motors are generally fractional- horsepower motors used for low-torque applications such as operating fans and blowers.

13. Which of the following are advantages of shaded pole Motor

  1. Economical
  2. High starting torque
  3. High running torque
  4. All of the above

Answer.1. Economical

Explanation:- The Advantages of shaded pole Motor are

  • Simplest construction, no need for capacitor or centrifugal switch.
  • Long life Less starting current and it does not cause a voltage drop across the nearest feeder.
  • Easy to rewind and maintenance-free motors.
  • It does not require any special starting methods.

The shaded pole induction motor has no commutator, brushes, collector rings, contactors, capacitors or moving switch parts, so it is relatively cheaper, simpler and extremely rugged in construction and reliable. The absence of a centrifugal switch eliminates the possibility of motor failure due to faulty centrifugal switch mechanisms.

14. The main disadvantages of shaded pole motor are

  1. Low power Factor
  2. Low starting torque
  3. Low efficiency
  4. All of the above

Answer.4. All of the above

Explanation:

The main disadvantages of shaded pole motor are

  • Low power factor.
  • The starting torque is very poor.
  • The efficiency is very low as the copper losses are high due to the presence of the copper band.
  • The speed reversal is also difficult and expensive as it requires another set of copper rings.

15. The shaded pole motor are found useful in application for

  1. Exhaust fan
  2. Hair dryer
  3. Film projectors
  4. All of the above

Answer.4. All of the above

Explanation: Shaded pole motors are induction motors manufactured for very small ratings and are used in applications where starting torque requirement of the load is very low. Some of the applications of shaded pole type induction motors  are air blowers, fans used in heaters, slide and film projectors, advertising display devices etc.

  • They are suitable for small devices like relays and fans because of their low cost and easy starting.
  • Used in exhaust fans, hair dryers, and also table fans.
  • Used in air conditioning and refrigeration equipment and cooling fans.
  • Used in record players, tape recorders, projectors, photocopying machines.
  • Used for starting electronic clocks and single-phase synchronous timing motors.

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