Question

phase induction motor is wound for 4 poles and is supplied from 50 Hz system. Calculate (i) Synchronous speed (ii) rotor speed when slip is 4% (iii) rotor frequency when rotor runs at 600 rpm.

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Answer 1

1. given answer is correct

Answer 2

The Synchronous speed is 1500 RPM, rotor speed when slip is 4% is 1440 RPM, and rotor frequency when rotor runs at 600 RPM is 30 Hz.

Given,

A phase induction motor is wound for 4 poles and is supplied from 50 Hz system.

To Find,

The Synchronous speed, rotor speed when slip is 4%, and rotor frequency when rotor runs at 600 RPM.

Solution,

Using the formula of synchronous speed

Ns = 120*f/P

where f is the frequency and P is the number of poles.

Ns = 120*50/4

Ns = 1500 RPM

Now,

Rotor speed = N = Ns(1-s)

N = 1500(1-0.04)

N = 1440 RPM

Now, when the rotor speed is 600 RPM, then slip will be

S = (Ns-N)/Ns

S = (1500-600)/1500

S = 0.6

Rotor frequency = sf = 0.6*50 = 30 Hz.

Hence, the Synchronous speed is 1500 RPM, rotor speed when slip is 4% is 1440 RPM, and rotor frequency when rotor runs at 600 RPM is 30 Hz.

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