INDUCTION MOTOR > V\ 29

gradually building up to the primary circuit.
hereof is, that the current in every secondary circuit is in pha~se
with the true induced voltage of this circuit, and is i\ = -A
TI
where TI is the resistance of the circuit. As ei is the voltage
induced by the resultant of the mutual magnetic flux coming
from the primary winding, and the self-inductive flux corre-
sponcling to the i&i of the secondary, the reactance, Xi, does not
enter any more in the equation of the current, and e\ is the
voltage due to the magnetic flux which passes beyond the cir-
cuit in which e\ is induced. In the usual induction-motor theory,
the mutual magnetic flux, <^, induces a voltage, E, which produces
a current, and this current produces a self -inductive flux, <$>'j,
giving rise to a counter e.m.f. of self-induction 7i#i, which sub-
tracts from E. However, the self-inductive flux, <£'i, interlinks
with the same conductors, with which the mutual flux, $, inter-
links) and the actual or resultant flux interlinkage thus is $1 =
$ — <^'i, and this produces the true induced voltage e\ = E —
7j#i, from which the multiple squirrel-cage calculation starts.1
Double Squirrel-cage Induction Motor
20. Let, in a double squirrel-cage induction motor :
.$2 = true induced voltage in inner squirrel cage, reduced
to full frequency,
/2 = current, and
Z2 = r2 + jxi = self-inductive impedance at full frequency,
reduced to the primary circuit.
$1 = true induced voltage in outer squirrel cage, reduced
to full frequency,
Ji = current, and
Zl = n + jxi = self-inductive impedance at full frequency,
reduced to primary circuit.
$ = voltage induced in secondary and primary circuits by
mutual magnetic flux,
j??o = voltage impressed upon primary,
Jo = primary current,
ZQ = r0 + JXQ = primary self -inductive impedance, and
Fo = g — jb = primary exciting admittance.
xSee ''Electric Circuits", Chapter XIL Reactance of Induction
Apparatus,
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