324

ELECTRICAL APPARATUS

, ^ o

cos (on — 0) = — c,

c =

(92)
(93)

Since r0 is usually very much smaller than Zi, if c is not very
large, it is:

cos (ai — 0) ~ o]
nence:

B = 90° - «!. (94)

That is, if the brush angle, 6, is complementary to the phase
angle of the self-inductive rotor impedance, ai, the motor tends
toward approximate synchronism at no-load.

Hence:

At given brush angle, 6, a value of secondary impressed e.m.f.,
C.EQ, exists, which makes the motor tend to synchronize at no-
load (93), and,

At given rotor-impressed e.m.f., cE^ a brush angle, 0, exists,
which makes the motor synchronize at no-load (92).

185. 3. In the general equations of the polyphase shunt motor,
the stator current, equation (78) :

' $Z + Zi + dcZ

, ,
(95)

be resolved into a component:

" sZ +

ZZ,

which does not contain c, and is the same value as the primary
current of the polyphase induction motor, and a component:

"

° o sZZ0 + ZZ,
Resolving /"o, it assumes the form :

(96)

= c { Ai cos B + A2 sin (9) + j (Ai sin 0 — A2 cos ^) }. (97)
This second component of primary current, 7"o, which is pro-

duced by the insertion of the voltage,
cuit, so contains a power component :

i'o = c (Ai cos 6 + A2 sin

, into the secondary cir-
(98)