Product Manual

Permanent Magnet (PMAC) Motors
The PMAC (Permanent Magnet AC) motor is traditionally of a more
complex construction than the standard induction motor. With the
new motor type, the design has been simplified by using powerful
permanent magnets to create a constant flux in the air gap, thereby
eliminating the need for the rotor windings and brushes normally used
for excitation in synchronous motors. This results in the accurate perfor-
mance of a synchronous motor, combined with the robust design of a
standard induction motor. The motor is energized directly on the stator
by the variable speed drive.
Benefits of a PMAC Motor
Standard induction motors are not particularly well suited for low-speed
operation as their efficiency drops with the reduction in speed. They
may also be unable to deliver sufficiently smooth torque across the
lower speed range. This is normally overcome by using a gearbox. The
new solution provides a high torque drive coupled directly to the load.
By eliminating the gearbox, the user saves space and installation costs,
as he only needs to prepare the foundations for one piece of machinery.
This also gives more freedom in the layout design.
The PMAC motor can deliver more power from a smaller unit. For
instance, powering the in-drives of a paper machine directly at 220
to 600 r/min with a conventional induction motor would require a
motor frame substantially larger than that of a 1500 r/min motor. Using
permanent magnet motors also means higher overall efficiency and less
maintenance.
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