PASCO SE-8658A PERMANENT MAGNET MOTOR - Manual (Page 23)

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012-07210A Permanent Magnet Motor
EQUIPMENT NEEDED
• Permanent Magnet Motor • multimeter
• patch cords • corrugated cardboard
• Digital Stroboscope or • power source that will deliver both
Digital Photogate Timer DC and AC current limited to 1.0 A
Purpose
The purpose of this experiment is to demonstrate the operation of an AC synchronous motor in terms of
basic concepts of electromagnetism.
Theory
The field magnets (permanent magnets) may be
thought of as possessing north and south poles that
interact with the north and south poles of the armature
(an electromagnet). Like poles repel, while unlike
poles attract. The armature rotates until its north pole
is as close as possible to the south pole of the
permanent magnet (and also as far as possible from
the north pole). At that moment, the alternating
current reverses its direction in the armature. The
poles likewise reverse, promoting another half-turn of
the armature.
A better explanation involves an understanding of
fields. The field magnets produce a magnetic field
that passes through the gap between the poles. When
current passes through the turns of the armature in the
presence of the field, forces act to cause a torque that
rotates the armature. Inertia carries the armature past
the position of no torque to the point where the torque
would force the armature back in the other direction.
Instead, if the rotational speed of the armature matches
the frequency of the alternating current, the direction
of current in the armature will reverse at that instant,
so that the torque continues to act in the original
direction.
Setup
Gently lower the armature onto the shaft with the dual
slip-ring commutator down. Carefully rotate the
armature back and forth to separate the brushes and
Experiment 3: Operation of an AC Synchronous Motor
Figure 3.1
Installation of the Permanent Magnet Motor
onto the Field Magnets
armature
brushes
split ring
commutator
retaining nut
shaft
field
magnets
dual slip-ring
commutator