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Rotor emf and frequency at 1460 rpm

Short answer

Synchronous speed 1500 rpm, slip = 0.02667. Rotor phase emf = 288.68 V × slip = 7.70 V (line 13.33 V). Rotor frequency = 1.33 Hz.

A 4-pole, 50 Hz, 3 phase induction motor with star connected rotor gives 500 V between the slip rings at standstill. Calculate the magnitude and frequency of emf induced per phase in rotor circuit at a speed of 1460 RPM.

Given: 4-pole, 50 Hz, star rotor, 500 V between slip rings at standstill, speed 1460 rpm.

Ns=120×504=1500 rpm,s=1500−14601500=0.02667N_s = \frac{120\times 50}{4} = 1500\ \text{rpm}, \qquad s = \frac{1500 - 1460}{1500} = 0.02667

Standstill emf per phase (star):

E2=5003=288.68 VE_2 = \frac{500}{\sqrt3} = 288.68\ \text{V}

Rotor emf per phase at slip ss:

E2s=sE2=0.02667×288.68=7.70 VE_{2s} = sE_2 = 0.02667\times 288.68 = 7.70\ \text{V}

Rotor frequency:

fr=sf=0.02667×50=1.33 Hzf_r = sf = 0.02667\times 50 = 1.33\ \text{Hz}

Answer: emf per phase =7.70= 7.70 V (line value between slip rings =13.33= 13.33 V) and frequency =1.33= 1.33 Hz.

✓ Answer checked by Claude Opus 5.5 (high effort)

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