
Induction Motors - Rotating Field, Slip and Torque 169
convenient to continue to treat the flux as constant (for given
stator voltage and frequency) when we turn later to methods
of controlling the normal running speed.
It has to be admitted, however, that at high values of slip
(i.e.
low rotor speeds), we cannot expect the main flux to
remain constant, and in fact we would find in practice that
when the motor was first switched on, with the rotor station-
ary, the main flux might typically be only half what it was
when the motor was at full speed. This is because at high
slips,
the leakage fluxes assume a much greater importance
than under