0195136047.pdf

566 ROTATING MACHINES

speed. Returning to the analogy of a transformer, and considering that the rotor is coupled to the

stator in the same way the secondary of a transformer is coupled to its primary, we may draw the

equivalent circuit as shown in Figure 13.2.4.

Referring the rotor quantities to the stator, we can now draw the per-phase equivalent circuit

of the polyphase induction motor, as shown in Figure 13.2.5(a). The combined effect of the shaft

load and the rotor resistance appears as a reflected resistanceR 2 ′/S, which is a function of slip and

therefore of the mechanical load. The quantityR 2 ′/Smay conveniently be split into two parts:

R′ 2

S

=R 2 ′+

R′ 2 ( 1 −S)

S

(13.2.4)

R' 2

S

+

−

V 1 E 1 = E' 2

R 1 jXl^1 jX'l2

−jbm

R 1

+

−

Ic

gc

Im

I 1

I 0

I' 2

R' 2 (1 − S)

S

+

−

V 1 E 1 = E' 2

jXl 1 jX'l2 R' 2

−jbm

R 1

+

−

Ic

gc

Im

I 1

I 0

I' 2

R' 2 (1 − S)

S

+

−

V 1

jXl 1 jX'l2 R' 2

−jbm

I 1

I 0

I' 2

(a)

(b)

(c)

Figure 13.2.5Per-phase equivalent circuits of a polyphase induction motor, referred to the stator.