Problem 107-2    Source:  Problem prepared by the website author.

A three-phase induction motor of 220 V, 80 HP, 6 poles is connected to a network at 60 Hz and delivers rated power with 6% slip. Determine:

a) the speed of the rotating magnetic field;

b) the rotor frequency at rated load;

c) the speed of the rotor with rated load.

Solution of the Problem 107-2   

Item a

Calculating the speed of the rotating magnetic field is the same as calculating the synchronous speed of the motor. Using the eq. 107-02, repeated below, we can find the requested one.

Substituting for numerical values ​​and performing the calculation, we get:

Item b

The rotor frequency is given by eq. 107-07, repeated below.

Substituting for numerical values ​​and performing the calculation, we get:

Item c

The rotor speed is given by eq. 107-05, repeated below.

Substituting for numerical values ​​and performing the calculation, we get: