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I U

332 ELEMENTS OF ELECTRICAL ENGINEERING

where the magnetic field is practically a uniformly rotating field
of constant intensity, that is, the quadrature flux produced by
the armature magnetization equal to the main magnetic flux
produced by the impressed e.m.f.

If an accurate calculation of the motor at intermediate speed
and at standstill is required, the changes of effective exciting
admittance and of secondary impedance, due to the decrease
of the quadrature flux, have to be considered.

At synchronism the total exciting admittance gives the m.m.f.
of main flux and auxiliary flux, while at standstill the quad-
rature flux has disappeared or decreased to that given by the
starting device, and thus the total exciting admittance has de-

0.3J

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,_.

8LP,8-

Z

1.0 0.9 0.3 0.7 0.6 0.5 0.4 0.3 0.2

FIG. 183.—Three-phase induction motor on single-phase circuit, torque

curves.

creased to one-half of its synchronous value, or one-half plus the
exciting admittance of the starting flux.

The effective secondary impedance at synchronism is the joint
impedance of all secondary circuits; at standstill, however, only
the joint impedance of the projections of the secondary coils on
the direction of the main flux, that is, twice as large as at syn-
chronism. In other words, from standstill to synchronism the
effective secondary impedance gradually decreases to one-half
its stan5still value at synchronism.

For fuller discussion hereof the reader must be referred to my
second paper on the Single-phase Induction Motor, Transactions
A. I. E. E., 1900, page 37.

The torque in Fig. 182 obviously slopes toward zero at stand-