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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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Slip ring induction motor has
Wound rotor
Cage rotor
Shorted rotor
All of above
Wound rotor
A slip ring induction motor, also known as a wound rotor induction motor, utilizes a rotor constructed with a three-phase distributed winding similar to the stator. The ends of these windings are connected to slip rings, allowing external resistance to be added to the rotor circuit.
A slip ring induction motor, also known as a wound rotor induction motor, utilizes a rotor constructed with a three-phase distributed winding similar to the stator. The ends of these windings are connected to slip rings, allowing external resistance to be added to the rotor circuit.
Tst∝R2°2+(sX2)2sR2 — Torque equation showing dependence on rotor resistance R2
Tmax∝2X21 — Maximum torque is independent of rotor resistance
The external resistance connected via slip rings increases the rotor circuit resistance during starting. According to the torque equation, increasing rotor resistance shifts the maximum torque point closer to the starting condition, providing high starting torque and lower starting current. As the motor gains speed, this external resistance is gradually cut out to improve running efficiency.
Slip ring motors are used for high starting torque applications.
External resistance allows control over starting current and torque.
Higher maintenance requirements due to carbon brushes and slip rings.
High starting torque capability
Adjustable speed and torque characteristics
Low starting current draw
Higher cost and construction complexity
Requires periodic maintenance of brushes and rings
Lower efficiency compared to squirrel cage rotors
Cranes and hoists
Elevators
Conveyors and compressors
| Feature | Slip Ring | Squirrel Cage |
|---|---|---|
Rotor Type | Wound Rotor | Cage Rotor |
Slip rings are made of phosphor bronze and brushes are typically graphite or carbon.
Option B (Cage rotor) refers to the squirrel cage induction motor, which is simpler and more robust but lacks external control.
Option C (Shorted rotor) describes the state of a squirrel cage rotor or a wound rotor during normal operation (when slip rings are shorted).
A is correct — The slip ring induction motor is characterized by a wound rotor construction with external connection capability via slip rings.
Always remember that increasing external rotor resistance increases the starting torque but decreases the full-load efficiency; hence, it is only used during the start-up phase.