AC Motors

1
Forging new generations of engineers
2
AC Motors

• Instructional Plan

3
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

4
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

5
Synchronous Motors

• Operation of the synchronous motor
• At the positive ac peak voltage, the magnetic
  field strength is the greatest for the
  half-cycle.
• As the positive peak voltage drops to zero, the
  magnetic field strength weakens.
• Current reverses at the zero peak voltage
• The magnetic field strength will start building
  in the opposite direction.
• At the peak of the negative voltage, the field
  strength is again at the peak for that half
  cycle.
• The rate of reversals of the lines of force is
  determined by the frequency of the ac voltage.

6

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.

7
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.
• Speed depends on the frequency of the ac voltage
• Rotor can be operated clockwise or counter
  clockwise.