Popular Science: What is a Single-Phase Motor? The Widely Used Electrical "Little Expert"
Time:
2022-07-28
In modern electrified life and production, motors serve as key devices that convert electrical energy into mechanical energy. Among the many types, single-phase motors play an indispensable role in various fields due to their unique advantages.
In modern electrified life and production, motors serve as key devices that convert electrical energy into mechanical energy. There are many types, among which single-phase motors play an indispensable role in various fields due to their unique advantages. Recently, with continuous technological progress, the related technologies and applications of single-phase motors have once again attracted attention. Let's take a closer look at this common yet very important electrical device.
Single-phase motor, fully named small-power single-phase asynchronous motor, generally refers to a motor powered by a single-phase AC power supply (AC220V). Its structure is relatively simple, usually equipped with two-phase windings on the stator, and the rotor adopts a common squirrel-cage design. It is precisely based on the distribution difference of the two-phase windings on the stator and the different power supply conditions that single-phase motors have diverse starting and operating characteristics.
From the working principle perspective, when single-phase sinusoidal current passes through the stator winding, an alternating magnetic field is generated inside the motor. The intensity and direction of this magnetic field vary sinusoidally over time but remain fixed in spatial orientation, hence called an alternating pulsating magnetic field. This alternating pulsating magnetic field can be decomposed into two rotating magnetic fields with the same speed but opposite rotation directions. When the rotor is stationary, these two rotating magnetic fields produce equal and opposite torques in the rotor, resulting in a net torque of zero, so the motor cannot start by itself. However, if an external force causes the motor to rotate in a certain direction, for example clockwise, the cutting magnetic flux movement between the rotor and the clockwise rotating magnetic field weakens, while that with the counterclockwise rotating magnetic field intensifies, breaking the balance, and the rotor will continue to rotate in the pushed direction.
To enable the single-phase motor to start automatically, a common approach is to add a starting winding in the stator. The starting winding is spatially positioned 90 degrees apart from the main winding and connected in series with an appropriate capacitor, so that the currents in the two windings approximately differ by 90 degrees in phase, applying the phase-splitting principle. When two currents with a 90-degree phase difference in both time and space flow into the corresponding windings, a rotating magnetic field is generated in space. Under the action of this rotating magnetic field, the rotor can start automatically. After the speed rises to a certain level, the starting winding is disconnected by a centrifugal switch installed on the rotor or other automatic control devices, and only the main winding works during normal operation. Of course, in practical applications, there are many cases where the starting winding is not disconnected; such motors are called capacitor-type single-phase motors. To change their rotation direction, simply change the position of the capacitor connection.
Additionally, there is another method to generate a rotating magnetic field—the shaded pole method, and motors made this way are called single-phase shaded pole motors. The stator of this type of motor is usually made with salient poles, divided into two-pole and four-pole types. Each magnetic pole has a small slot at 1/3 to 1/4 of the full pole face, dividing the pole into two parts. A short-circuited copper ring is installed on the smaller part, effectively shading this part of the pole, hence the name. When the stator winding is energized, the main magnetic flux is generated in the pole. According to Lenz's law, the main magnetic flux passing through the short-circuited copper ring induces an eddy current in the ring with a phase lag of 90 degrees. The magnetic flux generated by this current also lags the main flux in phase, acting similarly to the starting winding of a capacitor motor, producing a rotating magnetic field that drives the motor to operate.
In practical applications, single-phase motors are ubiquitous. In daily life, household appliances are an important application area. Devices such as electric fans, hair dryers, exhaust fans, washing machines, refrigerators, and air conditioners all rely on single-phase motors to provide power. These household appliances have entered thousands of homes, greatly improving people's quality of life, and single-phase motors, as core power components, ensure the stable operation of these appliances.
In the production field, single-phase motors also play a significant role. Small equipment such as micro water pumps, pulping machines, threshers, crushers, woodworking machinery, and medical devices often use single-phase motors as driving devices. Although their power is relatively small, they play a key role in meeting small-scale production needs and improving production efficiency.
Single-phase motors, with their simple structure, low cost, and ease of use, have become widely used basic equipment in the electrical field. With continuous technological development, research on single-phase motor technology is deepening, and more breakthroughs are expected in efficiency improvement and performance optimization in the future, further expanding their application scope and bringing more convenience to people's lives and production.
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