CHAPTER V
SINGLE-PHASE INDUCTION MOTOR
60. As more fully discussed in the chapters on the single-phase
induction motor, in " Theoretical Elements of Electrical Engineer-
ing" and " Theory and Calculation of Alternating-current
Phenomena/' the single-phase induction motor has inherently,
no torque at standstill, that is, when used without special device
to produce such torque by converting the motor into an unsym-
metrical ployphase motor, etc. The magnetic flux at standstill
is a single-phase alternating flux of constant direction, and the
line of polarization of the armature or secondary currents, that
is, the resultant m.m.f. of the armature currents, coincides with
the axis of magnetic flux impressed by the primary circuit.
When revolving, however, even at low speeds, torque appears in
the single-phase induction motor, due to the axis of armature
polarization being shifted against the axis of primary impressed
magnetic flux, by the rotation. That is, the armature currents,
lagging behind the magnetic flux which induces them, reach
their maximum later than the magnetic flux, thus at a time when
their conductors have already moved a distance or an angle
away from coincidence with the inducing magnetic flux. That in,
if the armature currents lag ~ = 90° beyond the primary main
flux, and reach their maximum 90° in time behind the magnetic
flux, at the slip, s, and thus speed (1 — s), they reach their maxi-
mum in the position (1 — s) ~ = 90 (1 — s) electrical dogrooH
behind the direction of the main magnetic flux. A component
of the armature currents then magnetizes in the direction at
right angles (electrically) to the main magnetic flux, and th<i
armature currents thus produce a quadrature magnetic fhxx,
increasing from zero at standstill, to a maximum at synchronism,
and approximately proportional to the quadrature component of
the armature polarization, P:
P sin (1-8) |-
93