Single-Phase Motor: Working Principle, Types, and Uses
How Does a Single-Phase Motor Work?
A single-phase induction motor consists of a single-phase winding on the stator and a cage winding on the rotor. When a supply is connected to the stator winding, a magnetic field is produced.
Why Aren’t Single-Phase Motors Self-Starting?
When single-phase AC supply is given to the stator winding, it produces alternating flux, which alternates along one space axis only. It is not a rotating flux; hence, a single-phase induction motor is not self-starting.
Why is a Capacitor Used in a Single-Phase Motor?
Because there is no rotating stator magnetic field, a single-phase induction motor has no starting torque. The idea behind capacitor-start single-phase motors is an extension of the split-phase winding technique used to produce the starting torque in a single-phase induction motor.
What Are Single-Phase Motors Used For?
Single-phase motors are used in equipment and machines that are smaller in size and require lower horsepower (for example, one horsepower), such as pumps, refrigerators, fans, and portable drills.
Advantages of Single-Phase Motors
Single-phase motors are more economical than a 3-phase system and easily meet the power requirement. They are simple in construction, cheap in cost, reliable, and easy to repair and maintain.
Types of Single-Phase Induction Motors
Split-phase induction motor
Capacitor-start induction motor
Capacitor-start capacitor-run induction motor (two-value capacitor method)
Permanent split capacitor (PSC) motor
Shaded-pole induction motor
Universal Motors and Series-Wound Motors
A universal motor is a design that can operate on either AC or DC power. In universal motors, the stator and rotor of a brushed DC motor are both wound and supplied from an external source, with the torque being a function of the rotor current times the stator current. Reversing the current in both rotor and stator does not reverse the rotation. Universal motors can run on AC as well as DC, provided the frequency is not so high that the inductive reactance of the stator winding and eddy current losses become problems. Universal motors are compact, have high starting torque, and can be varied in speed over a wide range with relatively simple controls such as rheostats and PWM choppers.
Compared with induction motors, universal motors do have some drawbacks inherent to their brushes and commutators: relatively high levels of electrical and acoustic noise, low reliability, and more frequent required maintenance.
Faraday’s Law of Electromagnetic Induction
EMF gets induced in the rotor. As the rotor circuit is closed, current starts flowing in the rotor. This current is called the rotor current. This rotor current produces its flux, called rotor flux. Since this flux is produced due to the induction principle, the motor working on this principle got its name as an induction motor. Now there are two fluxes: one is main flux, and another is called rotor flux. These two fluxes produce the desired torque, which is required by the motor to rotate.