A 4-pole 50 Hz induction motor runs at 1455 rpm. What is the slip speed?

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ISRO IPRC Technical Assistant Mechanical 28 Aug 2016 Official Paper
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  1. 55 rpm
  2. 50 rpm
  3. 45 rpm
  4. None of these

Answer (Detailed Solution Below)

Option 3 : 45 rpm
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Detailed Solution

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Concept:

The speed difference between Synchronous Speed (Ns) and Rotor speed (Nr) is called slip speed. It is given by:

Slip speed = Ns - Nr

Synchronous speed is given by:

\({N_s} = \frac{{120 \times f}}{p} \)

where f  is frequency and p is number of pole

Calculation:

Given:

p = 4 and f = 50 Hz

\({N_s} = \frac{{120 \times f}}{p} = \frac{{120 \times 50}}{4} = 1500\;rpm\)

Slip speed = Ns - Nr = 1500 - 1455

Slip speed = 45 rpm

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