0195136047.pdf

13.2 INDUCTION MACHINES 577

Te=

If^2 ( 1 −S)

ωmS

R′ 2 −

Ib^2 ( 1 −S)

ωm( 2 −S)

R′ 2 (13.2.21)

The following example illustrates the usefulness of the equivalent circuit in evaluating the
motor performance.

+

−

V

R 1 jXl 1

j0.5Xm

j0.5X'l 2

j0.5Xm

(a)

(b)

Zf

Zb

If

Ib

I 1

0.5R' 2

S

j0.5X'l 2

0.5R' 2

2 − S

Torque

Speed

Torque due to

forward rotating field

Torque due to backward rotating field

Resultant torque

Figure 13.2.11Single-phase in-

duction motor based on the

revolving-field theory.(a)Equiva-

lent circuit.(b)Torque–speed char-

acteristics.

EXAMPLE 13.2.4

A^1 / 4 -hp, 230-V, 60-Hz, four-pole, single-phase induction motor has the following parameters and
losses:R 1 = 10 ,Xl 1 =Xl′ 2 = 12. 5 , R 2 ′= 11. 5 , andXm= 250 . The core loss at 230 V
is 35 W and the friction and windage loss is 10 W. For a slip of 0.05, determine the stator current,