Single-phase motors generally refer to low-power single-phase asynchronous motors powered by single-phase AC power (AC220V). Single-phase asynchronous motors usually have two-phase windings on the stator, and the rotor is a common squirrel cage type. The distribution of the two-phase windings on the stator and the different power supply conditions can produce different starting characteristics and operating characteristics.
When a single-phase sinusoidal current passes through the stator windings, the motor generates an alternating magnetic field. The strength and direction of this magnetic field change sinusoidally with time, but it is fixed in space orientation, so this magnetic field is also called alternating Pulsating magnetic field. This alternating pulsating magnetic field can be decomposed into two rotating magnetic fields with the same speed and opposite rotation directions. When the rotor is stationary, these two rotating magnetic fields produce two torques of equal magnitude and opposite directions in the rotor, making the synthesis The torque is zero, so the motor cannot rotate. When we use external force to rotate the motor in a certain direction (such as clockwise rotation), then the movement of the cutting magnetic field between the rotor and the rotating magnetic field in the clockwise rotation direction becomes smaller; the rotation between the rotor and the rotating magnetic field in the counterclockwise rotation direction The movement of the cutting magnetic field becomes larger. In this way, the balance is broken, the total electromagnetic torque generated by the rotor will no longer be zero, and the rotor will rotate in the pushing direction.
For the national standard single-phase motor to enable the single-phase motor to rotate automatically, we can add a starting winding to the stator. The starting winding is 90 degrees different from the main winding in space. The starting winding should be connected with a suitable capacitor in series The currents of the windings are approximately 90 degrees out of phase, which is the so-called split-phase principle. In this way, two currents that differ in time by 90 degrees into two windings that differ in space by 90 degrees will generate a (two-phase) rotating magnetic field in space. Under this rotating magnetic field, the rotor can start automatically. After starting, when the rotation speed rises to a certain level, the starting winding is disconnected by means of a centrifugal switch or other automatic control device installed on the rotor, and only the main winding works during normal operation. Therefore, the starting winding can be made into a short-term working mode. But in many cases, the starting winding is not disconnected. We call this motor a single-phase motor. To change the direction of this motor, just change the terminal of the auxiliary winding.
In single-phase motors, another method of generating a rotating magnetic field is called the shaded pole method, also known as the single-phase shaded pole motor. This kind of motor stator is made into salient pole type, there are two kinds of poles and four poles. Each magnetic pole has a small slot at the 1/3-1/4 full pole surface, which divides the magnetic pole into two parts, and a short-circuit copper ring is put on the small part, as if to cover this part of the magnetic pole, So it is called shaded pole motor. The single-phase winding is set on the entire magnetic pole, and the coils of each pole are connected in series. When connected, the generated polarities must be arranged in sequence according to N, S, N, and S. When the stator winding is energized, the main magnetic flux is generated in the magnetic pole. According to Lenz's law, the main magnetic flux passing through the short-circuit copper ring generates an induced current lagging 90 degrees in phase in the copper ring. The pass also lags the main magnetic flux in phase, and its effect is equivalent to the starting winding of the capacitive motor, thereby generating a rotating magnetic field to rotate the motor.
When a single-phase sinusoidal current passes through the stator windings, the motor generates an alternating magnetic field. The strength and direction of this magnetic field change sinusoidally with time, but it is fixed in space orientation, so this magnetic field is also called alternating Pulsating magnetic field. This alternating pulsating magnetic field can be decomposed into two rotating magnetic fields with the same speed and opposite rotation directions. When the rotor is stationary, these two rotating magnetic fields produce two torques of equal magnitude and opposite directions in the rotor, making the synthesis The torque is zero, so the motor cannot rotate. When we use external force to rotate the motor in a certain direction (such as clockwise rotation), then the movement of the cutting magnetic field between the rotor and the rotating magnetic field in the clockwise rotation direction becomes smaller; the rotation between the rotor and the rotating magnetic field in the counterclockwise rotation direction The movement of the cutting magnetic field becomes larger. In this way, the balance is broken, the total electromagnetic torque generated by the rotor will no longer be zero, and the rotor will rotate in the pushing direction.
For the national standard single-phase motor to enable the single-phase motor to rotate automatically, we can add a starting winding to the stator. The starting winding is 90 degrees different from the main winding in space. The starting winding should be connected with a suitable capacitor in series The currents of the windings are approximately 90 degrees out of phase, which is the so-called split-phase principle. In this way, two currents that differ in time by 90 degrees into two windings that differ in space by 90 degrees will generate a (two-phase) rotating magnetic field in space. Under this rotating magnetic field, the rotor can start automatically. After starting, when the rotation speed rises to a certain level, the starting winding is disconnected by means of a centrifugal switch or other automatic control device installed on the rotor, and only the main winding works during normal operation. Therefore, the starting winding can be made into a short-term working mode. But in many cases, the starting winding is not disconnected. We call this motor a single-phase motor. To change the direction of this motor, just change the terminal of the auxiliary winding.
In single-phase motors, another method of generating a rotating magnetic field is called the shaded pole method, also known as the single-phase shaded pole motor. This kind of motor stator is made into salient pole type, there are two kinds of poles and four poles. Each magnetic pole has a small slot at the 1/3-1/4 full pole surface, which divides the magnetic pole into two parts, and a short-circuit copper ring is put on the small part, as if to cover this part of the magnetic pole, So it is called shaded pole motor. The single-phase winding is set on the entire magnetic pole, and the coils of each pole are connected in series. When connected, the generated polarities must be arranged in sequence according to N, S, N, and S. When the stator winding is energized, the main magnetic flux is generated in the magnetic pole. According to Lenz's law, the main magnetic flux passing through the short-circuit copper ring generates an induced current lagging 90 degrees in phase in the copper ring. The pass also lags the main magnetic flux in phase, and its effect is equivalent to the starting winding of the capacitive motor, thereby generating a rotating magnetic field to rotate the motor.
