Single-phase asynchronous motor

A single-phase asynchronous motor is a type of motor powered by a 220V single-phase AC power supply. It is suitable for small industrial equipment and household appliances with only single-phase power.

Working principle of single-phase asynchronous motor

In an AC motor, when AC current passes through the stator winding, armature magnetomotive force is established, which has a great influence on the energy conversion and operating performance of the motor. Therefore, when single-phase AC is passed through the single-phase AC winding, a pulsating magnetomotive force is generated, which can be decomposed into two rotating magnetomotive forces with equal amplitude and opposite speed, thereby establishing a positive and reverse magnetic field and in the air gap. These two rotating magnetic fields cut the rotor conductor and generate an induced electromotive force and an induced current in the rotor conductor respectively.

The interaction between the current and the magnetic field produces positive and negative electromagnetic torques. The positive electromagnetic torque attempts to make the rotor rotate forward; the negative electromagnetic torque attempts to make the rotor rotate backward. The superposition of these two torques is the synthetic torque that drives the motor to rotate.
Whether it is or, their size and slip ratio are the same as those of three-phase asynchronous motors. If the motor speed is,

For the positive magnetic field, the slip rate is:

For a reverse magnetic field, the slip is:

The Ts curve of a single-phase asynchronous motor is shown
in the figure on the left. The main characteristics of a single-phase asynchronous motor are as follows:
(1) n=0, s=1, T=T++ T- =0, indicating that the single-phase asynchronous motor has no starting torque. If no other measures are taken, the motor cannot start.
(2) When s≠1, T≠0, T has no fixed direction, it depends on the positive or negative value of s.
(3) Due to the existence of reverse torque, the synthetic torque also decreases, and the overload capacity of the drum single-phase asynchronous motor is low.

Working principle of shaded-pole single-phase motor
After the stator is supplied with current, part of the magnetic flux passes through the short-circuit ring and generates an induced current in it. The current in the short-circuit ring hinders the change of the magnetic flux, causing the magnetic flux generated by the part with the short-circuit ring and the part without the short-circuit ring to have a phase difference, thus forming a rotating magnetic field and causing the rotor to rotate.

The direction of rotation of the motor in the above figure is clockwise rotation, because the magnetic flux of the part without the short-circuit ring is ahead of the magnetic flux of the part with the short-circuit ring.

Working principle of capacitor phase-splitting
starting When starting, switch K is closed, so that the phase difference between the two winding currents I1 and I2 is about 90°, thereby generating a rotating magnetic field and the motor starts to rotate;
after normal rotation, the centrifugal switch is thrown off and the starting winding is cut off.

Use of single-phase asynchronous motor

Single-phase asynchronous motors have low power and are mainly made into small motors. They are widely used in household appliances (washing machines, refrigerators, electric fans), power tools (such as hand drills), medical equipment, automation instruments, etc.