i

10
thus:

ELECTRICAL APPARATUS

7. As seen, the torque curve has a very curious shape: a
maximum at 7 per cent, slip, and a second higher maximum at
standstill.

The torque efficiency is very high at all speeds, and prac-
tically constant at 82 per cent, from standstill to fairly close of
full speed, when it increases.

FIG. 4.—Speed curves of induction motor with eddy-current starting device.
But the power-factor is very poor, reaching a maximum of
78 per Gent.-only, and to get the output from the motor, required
rewinding it to give the equivalent of a \/3 times as high voltage.
For comparison, in dotted lines as T' is shown the torque curves
of the standard motor, of same maximum torque. As seen, in
the motor with eddy-current starting device, the slip at load is
very small, that is, the speed regulation very good. Aside from
the poor power-factor, the motor constants would be very
satisfactory.
The low power-factor seriously limits the usefulness of the
device.
By differently proportioning the eddy-current device to the
secondary circuit, obviously the torque curve can be modified