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##### 8.18 Solved Numerical Problems

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* Example 8.3* A 3 hp, three-phase, four-pole, 400 V, 50 Hz induction motor runs at 1440 rpm. What will be the frequency of the rotor-induced EMF?

**Solution:**

Rotor speed, N_{r} = 1440 rpm

Stator supply frequency, f = 50 Hz

Rotor induced EMF frequency, f_{r} = Sf

= 0.04 × 50

= 2 Hz

* Example 8.4* The frequency of the rotor-induced EMF of 400 V, three-phase, 50 Hz, six-pole induction motor is 2 Hz. Calculate the speed of the motor.

**Solution:**

Rotor frequency, f_{r} = Sf

or, 2 = S × 50

or, S = 0.04

Again,

Substituting values

or, N_{r} = 960 rpm

* Example 8.5* A slip-ring-type three-phase induction motor rotates at a speed of 1440 rpm when a 400 V, 50 Hz is applied across the stator terminals. What will be the frequency of the rotor-induced EMF?