Refer to
Figure 2.1 where
T,, =
starting torque or breakaway torque.
T, =
minimum, pull-in or pull-up torque.
Tpo =
pull-out, breakdown or maximum torque, obtainable over the entire speed range.
In a good
design this should occur as close to the rated slip as possible to ensure that
the motor runs safely, even during momentary overloads, load fluctuations
exceeding the load torque, or abrupt voltage fluctuations, without harmful slip
losses.
In some specially
designed rotors, however, to achieve a high starting torque sometimes the
pull-out torque Tpo may not be available on the speed-torque curve.
It is
possible that in such cases the T,, may be the highest torque developed by the
motor in the entire speed range (Figure 2.2).
T, = rated
or the full-load torque and should occur as near to the synchronous speed as
possible to reduce slip losses.
S = rated
slip at which occur the rated torque and current.
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