INDUCTION MOTOR

53

As seen, at full-load of 75 kw. output,
the efficiency is 80 per cent., which is fair for a slow-speed motor.

But the power-factor is 55 per cent., the apparent efficiency
only 44 per cent., and the exciting current is 75 per cent, of full-
load current.

This motor-load curve may be compared with that of a typical
induction motor, of exciting admittance:

7o = 0.01 - 0.1 j,

given on page 234 of " Theory and Calculation of Alternating-
current Phenomena" 5th edition, and page 319 of " Theoretical

LOW SPEED INDUCTION MOTOR
e0 = 500 Z0~.1+.3j

Y0=.02-.6j 2i=.1 +.3j

10 20 3.0 40 50 60 TO 80 9,0 100 110 120

MIPS.

.600

FIG. 20. — Low-speed induction motor, load curves.
Elements of Electrical Engineering," 4th edition, to. see the
difference.
39. In the synchronous machine usually the stator, in corn-
mutating machines the rotor is the armature, that is, the element
to which electrical power is supplied, and in which electrical
power is converted into the mechanical power output of the
motor. The rotor of the typical synchronous machine, and the
stator of the commutating machine are the field, that is, in
them no electric power is consumed by conversion into mechanical
work, but their purpose is to produce the magnetic field flux,
through which the armature rotates.
In the induction machine, it is usually the stator, which is the