- 2081 Chaitra (new course) · 4+2 marks
Slip ring vs squirrel cage induction motor
Short answer
Squirrel-cage rotor has shorted bars, simple, low starting torque, high starting current; used for fans, pumps. Slip-ring rotor has 3-phase winding with slip rings, external resistance gives high starting torque and low current; used for cranes, hoists, mills.
Mention the basic difference between slip ring and squirrel cage induction motor. Discuss their application and its characteristics.
Both are 3-phase induction motors with the same stator; they differ only in the rotor. A squirrel-cage rotor has short-circuited bars, while a slip-ring rotor has a 3-phase winding brought out through slip rings.
Basic differences
| Point | Squirrel cage | Slip ring (wound rotor) |
|---|---|---|
| Rotor winding | Bars shorted by end rings | 3-phase star winding |
| Slip rings, brushes | Absent | Present |
| External resistance | Cannot be added | Can be added in rotor |
| Construction | Simple, robust | Complex |
| Cost and maintenance | Low | High (brushes wear) |
| Starting torque | Low to moderate | High (adjustable) |
| Starting current | High (5–7 × FL) | Low with rotor resistance |
| Speed control | Not from rotor | Possible by rotor resistance |
| Efficiency, pf at running | Better | Slightly lower |
Characteristics
- Squirrel cage: low rotor resistance gives small full-load slip (2–5%), so it runs at nearly constant speed with good efficiency, but has low starting torque and high starting current. Double-cage and deep-bar designs improve starting torque.
- Slip ring: adding rotor resistance shifts maximum torque towards starting (), giving high starting torque with low starting current. In running the rings are shorted and it behaves like a cage motor. Speed can be reduced (with loss) by keeping resistance in.
Applications
- Squirrel cage: fans, blowers, pumps, lathes, drilling machines, compressors, conveyors — general constant-speed drives (about 90% of industrial motors).
- Slip ring: cranes, hoists, lifts, elevators, crushers, large compressors, mills — loads needing high starting torque or some speed control.
✓ Answer checked by Claude Opus 5.5 (high effort)
Related questions
- Slip ring motor max-torque slip and full-load output · Electrical Machines I, chapter 5 · asked 4×
- Maximum torque and torque at 1430 rpm of slip ring motor · Electrical Machines I, chapter 5 · asked 3×
- Slip for maximum torque and full-load output of slip ring motor · Electrical Machines I, chapter 5 · asked 2×
- Max-torque speed and efficiency of 400 V slip ring motor · Electrical Machines I, chapter 5 · asked 2×
- Effect of five-times rotor resistance on 40 kW slip ring motor · Electrical Machines I, chapter 5
- Max torque speed and Tmax/Tst of slip ring motor · Electrical Machines I, chapter 5
- Slip power recovery for slip ring induction motor · Utilization of Electrical Energy, chapter 3 · asked 2×
- 250 HP 1410 rpm slip ring motor (kw 0.955) · Electric Machine Design, chapter 4 · asked 6×
- 200 kW 1420 rpm slip ring motor (star) · Electric Machine Design, chapter 4 · asked 5×
- 250 HP 4-pole slip ring motor · Electric Machine Design, chapter 4 · asked 5×