Problem 107-9    Source:   Problem 5.7 - page 272 - SEN, P.C. -    Book: Principles of Electric Machines and Electronics - 3rd Edition - Ed. Wiley - 2014.

A three-phase induction motor of 460 V, 60 Hz and PF = 0.9 delayed, consumes a current of 25 A. The ventilation and friction losses are 300 W, the rotor copper losses are 400 W and the stator copper losses are 1,100 W. Determine:

a) the power in the air gap, P_gap ;

b) the mechanical power developed by the engine, P_mec ;

c) the output power, P_n ;

d) the efficiency of the engine.

Solution of the Problem 107-9   

Item a

With the problem data we can calculate the input power using the eq. 107-22. As the core losses were not provided, we will consider them zero. Then:

Item b

To calculate the mechanical power we will use the eq. 107-28.

Item c

Using the eq. 107-31 we can calculate the nominal power of the motor. Like this:

Carrying out the calculation, we get:

Item d

The efficiency of the machine can be calculated from eq. 107-23.

Carrying out the calculation, we get: