Transcript AC Motors - apolloteched / FrontPage

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AC Motors
Instructional Plan
Universal Motors
• Universal motors use armatures, brushes,
commutators, and field coils
• These motors can use ac or dc voltages.
• High torque and varying motor speed are two
properties of the universal motor
– Inductive reactance affects current flow in the coils
– The resistance of the coil to ac current flow requires greater ac
voltages to develop motor torque and speed
• Uses of universal motors
– Household appliances.
– Workshop tools such as electric drills
Synchronous Motors
• Do not have commutators and brushes
– Stators and rotors are used in synchronous motors.
• Stators are fields coils
• Rotors rotate within the stator.
– AC applied to the stator produces a constant reversal
of the magnetic lines of force
Synchronous Motors
Operation of the synchronous motor
At the positive ac peak voltage, the magnetic field
strength is the greatest for the half-cycle.
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As the positive peak voltage drops to zero, the magnetic
field strength weakens.
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Current reverses at the zero peak voltage
The magnetic field strength will start building in the
opposite direction.
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At the peak of the negative voltage, the field strength is
again at the peak for that half cycle.
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The rate of reversals of the lines of force is determined by
the frequency of the ac voltage.
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Synchronous Motors
The motor speed is synchronized to the ac
frequency.
– Rotors of made of soft iron disks are often used in
small synchronous motors.
– Rotors made of electromagnets require dc voltages
applied to the rotor to create north and south poles.
Synchronous Motors
Synchronous motors are usually not self-starting.
Some rotors use damper windings to cerate enough
torque to turn the rotor and start the motor.
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Speed depends on the frequency of the ac voltage
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Rotor can be operated clockwise or counter clockwise.