Single-phase motor
A single-phase motor has a total of two coils, a main coil and a sub-coil. When the single-phase sinusoidal current passes through the main coil, the main coil will produce an alternating pulsating magnetic field, and the strength of this magnetic field changes with time as the sinusoidal current changes, but in its direction has always been 1 to 3.
If there is no force provided by other coils, then the motor will not rotate after 90 degrees. If you want to rotate it, you must also add a force perpendicular to the direction of the main coil, provided by the starting coil, that is, the sub-coil.
In order for the sub-coil to provide a force perpendicular to the direction of the main coil, another phase of current must be introduced into the secondary coil. If the same phase current is passed through, then the direction of the force they generate is the same. But there is only single-phase electricity, so what to do?
At this time, it is necessary to use capacitor phase shifting. In simple terms, the capacitor is connected in series in the circuit where the phase shift is required, so that the current phase changes. After the single-phase AC phase is transferred, then its waveform pattern becomes the following figure.
Finally, put it together, the motor wiring diagram becomes the following figure. First the sinusoidal alternating current comes in from point A, part of which powers the main coil and the other part is phase-shifted through capacitance. Since the two phases of electricity are one after the other, the magnetic field force generated by the coil will also be one after the other. In this way, it is possible to reach the main coil and push it, then the sub-coil pushes it, and finally rotates it.
If you want the motor to reverse, you only need to change the power cord connected to point A in the above figure to point B, and the power line connected to point C does not move.
Because the main coil before the change is used with a sinusoidal alternating current with a phase of zero, the sub-coil uses the sinusoidal alternating current after phase shifting. After the power line is changed to point B, the secondary coil uses sinusoidal alternating current with zero phase, and the main coil uses sinusoidal alternating current after phase shifting. If the current phase of the two coils changes, the direction of the magnetic field force they generate also changes, and the rotation will also change.
Three-phase motor
Three-phase motors use three-phase AC power, due to three-phase AC they have a phase difference of 120°. When the stator winding is connected to a three-phase alternating current, a rotating magnetic field is generated within the stator. The rotating magnetic field cuts the rotor winding, then the rotor winding will generate an induced current, and the induced current will be subjected to electromagnetic force in the rotating magnetic field, which will rotate.
Three-phase motors use three-phase power supplies, and their phase difference is 120 degrees. We can simply understand that a three-phase motor is equivalent to three people standing at three different angles to push the rotor. The single-phase motor adopts a single-phase power supply and capacitor, and the phase difference between the main and secondary coils is 90 degrees. We can simply understand that a single-phase motor is equivalent to two people standing at two different angles to push the rotor.
Therefore, a three-phase motor with the same power has a larger torque (rotational force) than a single-phase motor.
Generally, if there is a three-phase power supply, try to use a three-phase motor, because the three-phase motor of the same power has the advantages of small size, light weight, low noise, low price and high torque compared with single-phase motors.
Disclaimer: The content and pictures in this article come from the Internet, please contact to delete the infringement.