What Is The Single-phase Motor?
1. Definition of single-phase motor
Single-phase motors refer to all types of motors that operate with a single-phase power supply.
Including single-phase induction motor, shield pole motor, split phase motor, capacitor start motor and so on.
The single-phase power supply itself does not produce a rotating magnetic field, so the single-phase motor requires an additional starting mechanism.
2. Definition of single-phase induction motor
The single-phase induction motor consists of a single-phase winding on the stator and a cage winding on the rotor.
After the stator winding is energized, a pulsating magnetic field is generated, but because of the pulsation of the magnetic field, the rotor can not start itself.
Special techniques, such as capacitive starting, are required to generate a quasi-rotating magnetic field to enable self-starting.
3. Working principle of single-phase induction motor
Based on the principle of electromagnetic induction, a pulsating magnetic field is generated when the stator winding is connected to the single-phase AC power supply.
Pulsating magnetic fields do not enable the rotor to start itself, so an auxiliary starting device is required.
Once the rotor starts to rotate, the motor will continue to rotate in the starting direction.
4. The structure of single-phase induction motor
Stator: The stationary part that generates a magnetic field. It consists of a laminated iron core with grooves and a stator winding.
Rotor: Rotating part, usually a cage type rotor, consisting of an aluminum or copper strip shorted ring.
5. Double rotating magnetic field theory
When a single-phase power supply is connected to the stator winding, two equal and opposite rotating magnetic fields are generated.
These two magnetic fields cancel each other out, creating a pulsating magnetic field that is unable to generate starting torque.
When the rotor begins to rotate, the magnetic field successively cuts the rotor conductors, creating an electromotive force and an electric current, which creates a starting torque.
6. Starting mode of single-phase induction motor
Single-phase induction motors do not start themselves and require additional starting devices (such as capacitors, split-phase windings, etc.) to generate starting torque.
7. Performance analysis
The performance of single-phase induction motor is analyzed by double rotating magnetic field theory and cross magnetic field theory.
These theories explain how the rotor generates torque once it begins to rotate.
8. Type of single-phase induction motor
Single-phase induction motors are divided into the following common types according to the starting method and working principle:
Split Phase Motor (Split Phase Motor) : The phase difference is generated by the windings of two different resistances to achieve startup.
Shaded Pole Motor (Shaded Pole Motor) : Use a conductor shield on the magnetic pole to delay part of the magnetic flux, introducing a phase difference.
Capacitor Start Motor: Start the capacitor in series in the auxiliary winding to increase the starting torque.
Permanent Split Capacitor Motor: A permanent capacitor is used for start-up and operation.
Capacitor Start Capacitor Run Motor: Uses dual capacitors (start and run) to provide maximum starting torque.
9. Application of single-phase induction motor
Single-phase induction motors are widely used in the following fields because of their simple structure, robustness and self-starting capability:
Household appliances: such as fans, blowers, blenders, grinders, etc.
Commercial equipment: such as commercial refrigerators, water pumps, air conditioners, etc.
Light industrial tools: such as metal processing, woodworking tools, etc.
Agricultural equipment: such as water pump, thresher, etc.
Small industrial equipment: such as CNC machine tools, lathes, drilling machines, etc.
Single-phase induction motors are particularly suitable for low-power (1/6 to 1/4 HP) applications that require frequent start-stop and moderate starting torque.
10. Advantages of single-phase induction motor
Economical benefits: simple structure, low cost.
Self-starting capability: single-phase power supply can be directly connected.
Rugged: maintenance-free cage rotor structure.
Lightweight and compact: suitable for household and light industrial applications.
Easy speed control: Speed control through external resistance.
Widely available: standard design and rating.
11. Disadvantages of single-phase induction motor
Low torque: only 60-65% of the maximum torque of the three-phase motor.
Low power factor: about 0.4 to 0.5, while three-phase motors are close to 1.
Vibration and noise: High vibration and noise due to torque pulsation.
Low efficiency: about 5% lower than the same three-phase motor.
Complex starting circuit: Special starting circuit is required, increasing cost and volume.
High starting current: The current drawn from the power supply at starting is 20-30% higher than normal operation.
