i!

58

•ELECTRICAL APPARATUS

In the synchronous motor, Fig. 21, D, produced from the induc-
tion motor, Fig. 21, C, it is:
Let:

70 == g — ft = primary exciting admittance

of the induction machine,
ZQ = r0 + jxo = primary self-inductive impe-
dance,

Zi = ri + j#i = secondary self-inductive im-
pedance.

/

— ........... v \ r
A A
/ v .....
/v-v—
AT-
i

\
— v\
A A

/
V^ A^

V N /

AAAr-

-A/W—

•M/V—
-A/W—

FIG. 21.—Starting of induction motor and conversion to synchronous.
The secondary resistance, n, is that of the field exciting winding,
thus does not further come into consideration in calculating the
motor curves, except in the efficiency, as I^TI is the loss of power
in the field, if i\ = field exciting current. Xi is of little further
importance, as the frequency is zero. It represents the magnetic
leakage between the synchronous motor poles.
r<) is the armature resistance and XQ the armature self-inductive
reactance of the synchronous machine.
However, XQ is not the synchronous impedance, which enters
the equation of the synchronous machine, but is only the self-
inductive part of it, or the true armature self-inductance. The