INDUCTION MOTOR

71

motor design, be considered as a high synchronous impedance
motor, while the good induction motor gives as synchronous
motor a synchronous impedance of several hundred per cent., that
is far beyond any value which ever would be considered in syn-
chronous-motor design.

Induction Motor Concatenated with. Synchronous

47. Let an induction machine have the constants :

YQ = g — jb = primary exciting admittance,
ZQ = TQ + JXQ = primary self-inductive im-
pedance,

Zi = n + jxi = secondary self-inductive im-
pedance at full frequency,
reduced to primary,

and let the secondary circuit of this induction machine be con-
nected to the armature terminals of a synchronous machine
mounted on the induction-machine shaft, so that the induction-
motor secondary currents traverse the synchronous-motor arma-
ture, and let:

Z% = r2 + J#2 = synchronous impedance of
the synchronous machine,
at the full frequency im-
pressed upon the induction
machine.

The frequency of the synchronous machine then is the fre-
quency of the induction-motor secondary, that is, the frequency
of the induction-motor slip. The synchronous-motor frequency

also is the frequency of synchronous-motor rotation, or - times

¥1

the frequency of induction-motor rotation, if the induction motor
has n times as many poles as the synchronous motor.
Herefrom follows:

- s

or:

s =

= 6',

1

n + 1

'(I)
1

that is, the concatenated couple runs at constant slip, s = __ -
thus constant speed,

l-s =

n

of synchronism.

(2)