PASCO SE-8657 MOTOR ACCESSORY - Manual (Page 37)

012-06247 A Motor Accessory
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You can use this experimental setup to demonstrate a hysteresis synchronous motor by dis-
connecting the leads to the brushes and attaching them to each other. In this configuration,
no current flows through the armature. Nonetheless, when 10 V, 12 Hz current is applied
to the field coils and the armature spun, it will continue to rotate in sync with the applied
current.
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You may want to challenge the students to predict and test what happen if DC is applied to
the armature while AC is applied to the coils. You can use this experimental setup to dem-
onstrate a hysteresis synchronous motor by disconnecting the leads to the brushes and at-
taching them to each other. In this configuration, no current flows through the armature.
Nonetheless, when 10 V, 12 Hz current is applied to the field coils and the armature spun,
it will continue to rotate in sync with the applied current.
•
You may want to challenge the students to predict and test what happen if DC is applied to
the armature while AC is applied to the coils.
➉ Counter-clockwise, as viewed from above.
The motor should turn clockwise.
The motor’s speed will decrease.
The motor should operate at a high rate of speed, but not in synchronism with the alternat-
ing current source. Reversing the direction of current flow from the power supply has no
effect on the motor’s operation, because a reversal of polarity will occur in BOTH the ar-
mature and field coils simultaneously, and any attraction or repulsion between poles will be
unaffected. The speed will be lower when the voltage is reduced.
The speed of the motor will decrease as the frequency is increased, clearly showing that it
is not operating in synchronism with the alternating current source. Coils resist changes in
current, and the greater the rate of change, the greater the “resistance”. This resistance is
properly termed inductive reactance. The inductive reactance of the coils is greater at
higher frequencies; thus less current flows and there is less power.
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