164

ELECTRICAL APPARATUS

the motors thus tend to keep in step until the common starting
resistance is short-circuited and the motors thereby become inde-
pendent, the synchronizing torque vanishes, and the motors can
slip against each other without interference by cross-curjrents.

Since the term—0~ - contains the slip, s, as factor, the syn-
chronizing torque decreases with increasing approach to syn-
chronous speed.

0.6 0.7

0.9 1.0

FIG. 59.—Synchronizing induction motors: motor torque and synchronizing

torque.

For r = 0, or with the motors in step with each other, it is, by
(12), (15), and (16):

z1 = seQ2g =

se02

__Jl2r)
Oi + sr-o + 2 r)2 + s2 (

(IS)

that is, the same value as found for a single motor. (As the
resistance r is common to both motors, for each motor it enters
as 2 r.)
For r = 90°, or the unstable positions of the motors, it is:

that is, the same value as the motor would give with short-