INDUCTION MOTOR

87

where:

{7,i = — j

m

and:

0,2 =

m

SX j-------*

m

(3)

All the further calculations of the motor characteristics now
are the same as in the straight induction motor.

As instance is shown the low-speed motor, Fig. 20, of constants:

60 = 500;

7o = 0.02 - 0.6 j;
Zo = 0.1 + 0.3 y;
Zl = 0.1 + 0.3 y;

with the secondary closed by a condenser of capacity impedance:

z2 = - 0.012 y,

thus giving:

Fig. 33 shows the load curves of this motor with condenser
in the secondary. As seen, power-factor and apparent effi-
ciency are high at load, but fall off at light-load, being similar
in character as with a commutating. machine concatenated to
the induction machine, or with the secondary excited by direct
current, that is, with conversion of the induction into a synchro-
nous motor.
Interesting is the speed characteristic: at very light-load the
speed drops off rapidly, but then remains nearly stationary over
a wide range of load, at 10 per cent. slip. It may thus be said,
that the motor tends to run at a nearly constant speed of 90 per
cent, of synchronous speed.
The apparent efficiency of this motor combination is plotted
once more in Fig. 28, for comparison with those of the other
motors, and marked by C.
Different values of secondary capacity give different operating
speeds of the motor: a lower capacity, that is, higher capacity