The single-phase induction motors are generally classified into six categories.
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Split Phase Induction Motors
Split phase induction motors are single phase motors that comprise of an auxiliary winding in addition to main winding in stator. The main winding is available during running and is given the name running winding. The major purpose of auxiliary winding is to start the motor and it is also named as starting winding.
The auxiliary and main windings are connected in parallel and are in space quadrature. A centrifugal switch is installed in circuit that serves to remove the auxiliary winding from circuit, once after the motor is started.
The two windings displaced from each other usually by an angle of 90° are supplied by two currents, the setting produces two-phase revolving field that in turn produces the necessary starting torque.
Also see: Slip Formula in an Induction Motor
Resistor split phase motors
The name resistance split phase is given to the motors based on the fact that phase displace is provided either by:
- Using a series resistor OR
- A high resistance starting winding
Characteristics/Working of Resistance Split Phase Motors
- Starting torque is about 1.5 to 2 times of full load value
- Starting winding is removed once motor achieves 75% of rated speed
Capacitor split phase motor
The phase displacement between two currents in capacitor split phase motors is provided by a capacitor that is connected in series with main starting winding. Capacitor split phase motors are further classified into three categories:
- Capacitor start motors: In such motors capacitor and starting winding is open circuit using centrifugal switch once the motor achieves 75% of rated speed
- Capacitor run motors: The capacitor remains in circuit for providing power factor improvement. Capacitor run motors are also sometimes given the name permanent capacitor motors.
- Capacitor start capacitor run Motor: Here two different capacitors are employed. One serves starting purpose, while other serves running. The motor is also referred as two-value capacitor motors
Also see: Applications of Induction Motors
Repulsion Motors
These motors carry a commutator winding. Once the motor reaches around 75% of rated speed, the centrifugal switch short circuits the commutator segments thereby turning the commutator winding to cage winding. Repulsion motors possess very good starting torque.
Shaded Pole Motors
In such motors a portion of motor’s salient pole is shaded by a short circuited copper ring, and hence the name shaded pole motors is given. The shaded pole setting serves to provide a phase displacement of about 20 to 30° between unshaded and shaded parts. Main winding in such motors is a concentrated winding that is installed on stators salient pole.
The shaded pole motors are employed for loads that need low starting torque. Loads up to 100 watts employ this type of motor.
Also see: Variable Frequency Drives