Repulsion Induction Motor operates on a combined principle of repulsion and induction. It consists of one stator winding, two rotor windings - one being a squirrel cage winding and the other a standard DC winding connected to a commutator, and a short-circuited pair of brushes.
This type of repulsion motor is gaining popularity due to its excellent all-around performance, which closely matches the characteristics of a compound DC motor.
- This motor is particularly well-suited for applications where the load can be completely disengaged, such as through de-clutching or using a loose pulley system.
- This motor, often called a squirrel-cage repulsion motor, combines the features of both repulsion and induction motors. It offers the advantageous characteristics of a repulsion motor along with the constant-speed performance of an induction motor.
This motor features the standard stator winding found in all repulsion motors but is unique with its two separate and independent rotor windings.
- Squirrel-cage winding and
- Commutator winding similar to that of a DC armature.
- Both rotor windings operate throughout the motor's entire runtime.
- The commutator winding is positioned in the outer slots, while the squirrel-cage winding is housed in the inner slots.
- At startup, the commutated winding provides most of the torque, as the squirrel-cage winding remains largely inactive due to its high reactance.
- As the rotor accelerates, the squirrel-cage winding gradually takes on a larger share of the load.
- The brushes in this motor are short-circuited and remain in continuous contact with the commutator.
- One key advantage is that it eliminates the need for a centrifugal short-circuiting mechanism.
- Additionally, some designs include a compensating winding to enhance the power factor, making the motor more efficient.
- This motor offers an exceptionally high starting torque, exceeding 300%, along with consistent speed regulation.
- It is widely used in applications such as household refrigerators, garage air pumps, petrol pumps, compressors, machine tools, mixing machines, lifts, and hoists.
- These motors can be reversed by the usual brush-shifting arrangement.
MCQs on Repulsion Induction Motor
1. Repulsion Induction Motor operates on which combined principle?
a) Repulsion and Synchronous
b) Induction and Synchronous
c) Repulsion and Induction
d) Induction and DC Motor
Answer: c) Repulsion and induction
2. How many rotor windings are present in a Repulsion Induction Motor?
a) One
b) Two
c) Three
d) Four
Answer: b) Two
3. What is the primary role of the commutator winding during startup in a Repulsion Induction Motor?
a) Reduces load torque
b) Provides most of the starting torque
c) Enhances speed regulation
d) Supplies constant speed
Answer: b) Provides most of the starting torque
4. Where is the squirrel-cage winding located in the rotor of a Repulsion Induction Motor?
a) Outer slots
b) Inner slots
c) Adjacent to brushes
d) Between stator coils
Answer: b) Inner slots
5. What is a key advantage of the brushes in a Repulsion Induction Motor?
a) They are removable
b) They eliminate the need for a centrifugal short-circuiting mechanism
c) They provide variable speed control
d) They reduce power loss significantly
Answer: b) They eliminate the need for a centrifugal short-circuiting mechanism
6. Why is the Repulsion Induction Motor gaining popularity?
a) High speed variability
b) Excellent all-around performance similar to a compound DC motor
c) Low cost compared to induction motors
d) Simple construction without compensating winding
Answer: b) Excellent all-around performance similar to a compound DC motor
7. What is the typical starting torque of a Repulsion Induction Motor?
a) 150%
b) 200%
c) 300%
d) 400%
Answer: c) 300%
8. Which application is NOT commonly associated with Repulsion Induction Motors applications?
a) Household refrigerators
b) Compressors
c) High-frequency alternators
d) Lifts and hoists
Answer: c) High-frequency alternators
9. What feature makes some Repulsion Induction Motors more efficient?
a) Larger stator windings
b) Centrifugal mechanism
c) Compensating winding to improve power factor
d) Adjustable brush position
Answer: c) Compensating winding to improve power factor
10. How can the rotation direction of a Repulsion Induction Motor be reversed?
a) By changing the stator winding polarity
b) By adjusting the commutator slots
c) By the usual brush-shifting arrangement
d) By modifying the squirrel-cage winding
Answer: c) By the usual brush-shifting arrangement