Single-phase motor rotation principle

Compared with the three-phase asynchronous motor, it is required to work under the single-phase power supply condition, and a winding structure suitable for a single-phase power supply is provided on the stator, and the rotor is a cage-type short-circuited rotor with a simple structure and reliability.

Single winding asynchronous motor

When a single-phase sinusoidal current passes through the stator windings, the single winding on the stator produces a pulsating magnetic potential, and the decomposition results in a rotating magnetic potential with equal positive and negative amplitudes.

● The motor is stationary

The short-circuited rotor (blocking state) has an equal effect on the positive and negative sequence potentials and generates a magnetic field (magnetic flux density) that is equal to the positive and negative sequence after the stator is synthesized. Thus, the positive value of the motor at the speed n=0 is generated. Reverse torque is also equal, ie

Tf=Tb

Starting torque of the motor

Tst= Tf-Tb=0

This means that single-winding single-phase asynchronous motors have no starting torque.

Double-winding single-phase asynchronous motor

In order to realize the single-phase motor can rotate automatically, the single-phase asynchronous motor is usually a two-winding motor.

● Resistor or capacitor start single-phase asynchronous motor

These two types of motors are collectively referred to as split-phase starting asynchronous motors. In addition to the main winding that determines the operating performance, there is a backup auxiliary auxiliary winding (referred to as the auxiliary winding).

When the starter motor is closed, the main and auxiliary windings are energized at the same time, generating a starting torque and the motor turning up. After the start-up process is completed, the secondary circuit is disconnected by the relay switch (cut off the start-up winding or the secondary winding), and the motor will only be operated by the main winding. The secondary windings of this type of motor are placed orthogonally to the main winding at 90 electrical angles in space, and also have non-orthogonal placement at any angle θ. The starting winding must be connected in series with a suitable capacitor so that the phase current is similar to that of the main winding. A difference of 90 degrees.

In order to produce a rotating magnetic field, in addition to requiring the two-phase windings to be different in space, there must be a phase difference in the phase of the current time. This requires that the proportional relationship between the loop resistance and the reactance of the secondary phase winding and the proportional relationship of the primary phase parameters are different. By increasing the secondary winding resistance to realize the phase shift between the primary and secondary phases, it is called a single-phase resistance starting asynchronous motor; a capacitor starting asynchronous motor depends on the secondary winding branch circuit connected in series to make the current of the two windings different.