- 2068 Magh · 8 marks
IM sync speed, slip, rotor frequency
Short answer
Synchronous speed N_s = 120×60/4 = 1800 rpm. Slip = (1800−1755)/1800 = 0.025 (2.5%). Rotor frequency = 0.025×60 = 1.5 Hz.
A 208 V, 60 Hz, 4 pole, 3-Ø induction motor has a full-speed of 1755 rpm. Calculate: (i) asynchronous speed, (ii) the slip and (iii) rotor frequency.
Given: 208 V, 60 Hz, 4-pole, 3-phase induction motor; full-load speed N = 1755 rpm.
(i) Asynchronous (synchronous) speed
N_s = 120 f / P = 120 × 60 / 4 = 1800 rpm (188.5 rad/s)
(ii) Slip
s = (N_s − N)/N_s = (1800 − 1755)/1800 = 45/1800 = 0.025 (2.5 %)
(iii) Rotor frequency
f₂ = s f = 0.025 × 60 = 1.5 Hz
| Quantity | Value |
|---|---|
| Synchronous speed | 1800 rpm |
| Slip | 0.025 |
| Rotor frequency | 1.5 Hz |
✓ Answer checked by Claude Opus 5.5 (high effort)
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