Problem 108-2    Source:   Problem prepared by the site authors.

A 220 V, 60 Hz network supplies 1,100 W to a 4-pole single-phase induction motor. The motor's nameplate states that FP = 0.85 and η = 0.9. Assuming that rotational losses are on the order of 140 W, find:

a) the electric current in the motor;

b) the nominal power of the motor;

c) the mechanical power of the motor.

Solution of the Problem 108-2   

Item a

To calculate the electric current in the motor we will use eq. 108- 29 shown below.

After some algebraic work, substituting numerical values and performing the calculation, we obtain:

Item b

Knowing the efficiency (or output) of the engine, η = 0.9, using eq. 108-30, we obtain:

Item c

Since we know the motor's nominal power and its losses, we can calculate the mechanical power using eq. 108-28. After an algebraic arrangement, we obtain: