Single-phase motor generally refers to a low-power single-phase asynchronous motor powered by a single-phase AC power supply. This kind of motor usually has two-phase windings on the stator and the rotor is a common squirrel-cage type. Different distribution of two-phase windings on the stator and different power supply conditions will produce different starting characteristics and operating characteristics.
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Single-phase motor refers to asynchronous motor powered by 220V AC single-phase power supply. Because the 220V power supply is very convenient and economical, and the domestic electricity consumption is also 220V, the single-phase motor is not only used in production, but also closely related to people's daily life, especially with the increasing improvement of people's living standards, the consumption of single-phase motors for household appliances is also increasing.
In terms of production, there are micro-pumps, refiners, threshers, shredders, woodworking machinery, medical instruments and so on. There are electric fans, hair dryers, exhaust fans, washing machines, refrigerators, etc. There are many kinds, but the power is small.
When a single-phase sinusoidal current passes through the stator winding, the motor will generate an alternating magnetic field. The intensity and direction of this magnetic field change sinusoidally at any time, but it is fixed in spatial orientation, so it is also called alternating pulsating magnetic field.
This alternating pulsating magnetic field can be decomposed into two rotating magnetic fields with the same rotating speed and opposite rotating directions. When the rotor is stationary, two rotating magnetic fields generate two torques with equal magnitude and opposite directions in the rotor, so that the resultant torque is zero, so the motor cannot rotate.
When we use external force to make the motor rotate in a certain direction, the movement of cutting magnetic lines between the rotor and the clockwise rotating magnetic field becomes smaller; The movement of cutting magnetic lines between the rotor and the rotating magnetic field in the counterclockwise direction becomes larger. In this way, the balance is broken, the total electromagnetic torque generated by the rotor is no longer zero, and the rotor will rotate in the direction of pushing.
To make the single-phase motor rotate automatically, we can add a starting winding in the stator, which is 90 degrees different from the main winding in space. The starting winding should be connected in series with a suitable capacitor, so that the current is about 90 degrees different from the main winding in phase.
The so-called phase separation principle. In this way, two currents with a time difference of 90 degrees flow into two windings with a space difference of 90 degrees, which will generate a (two-phase) rotating magnetic field in space.
Under the action of this rotating magnetic field, the rotor can start automatically. After starting, when the rotating speed rises to a certain level, the starting winding will be disconnected by centrifugal switch or other automatic control devices installed on the rotor, and only the main winding will work during normal operation.
Therefore, the starting winding can be operated for a short time. However, in many cases, the starting winding will not stop opening. We call this kind of motor a single-phase motor. To change the direction of this motor, just change the terminal of the auxiliary winding.
In single-phase motor, another method of generating rotating magnetic field is called shaded pole method, also known as single-phase shaded pole motor. The stator of this motor is made of salient poles, with two poles and four poles.
Each pole has a small slot on the whole pole surface of 1/3 ~ 1/4, which divides the pole into two parts and puts a short-circuit copper ring on the small part, as if to cover this part of the pole, so it is called a covered pole motor. The single-phase winding is sheathed on the whole pole, and the coils of each pole are connected in series. When they are connected, their polarities must be arranged in the order of n, s, n and s. ..
When the stator winding is energized, the main magnetic flux is generated in the magnetic poles. According to Lenz's law, an induced current is generated in the copper ring by short-circuiting the main flux of the copper ring, which lags behind the main flux by 90 degrees in phase. The magnetic flux generated by this current also lags behind the main magnetic flux in phase, which is equivalent to the starting winding of the capacitor motor, thus generating a rotating magnetic field to rotate the motor. ?
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