Asynchronous motor with single-phase AC power supply is called single-phase asynchronous motor.
Single-phase asynchronous motor requires only single-phase AC power, so it is convenient to use, widely used, and has the advantages of simple structure, low cost, low noise, low interference with the radio system, etc.
Therefore, it is often used in household appliances and small power machinery with little power, such as electric fans, washing machines, refrigerators, air conditioners, range hoods, electric drills, medical equipment, small fans and household water pumps, etc.
1. Classification of single-phase asynchronous motor
1、Resistance starter type single phase motors
Its stator is embedded with main phase winding and secondary phase winding, and these two windings and the axis in space into 90 degrees of electrical angle.
The secondary phase winding is usually strung with an applied resistor through the centrifugal opening, connected in parallel with the main phase winding, and connected to the power supply together.
When the single phase motor starts until the speed reaches 75% to 80% of the synchronous speed, the centrifuge opens and the centrifugal switch piece contact is de-energized.
2、Capacitor starting type single phase motors
It is basically the same as single-phase resistance starting motor, there are also two sets of windings on the stator with main phase and secondary phase at 90 degree electric angle.
The secondary winding and the external capacitor are connected to the centrifugal switch, parallel with the main winding, and connected to the electrical power supply together, also when 75%~80% of the synchronous speed is reached, the secondary winding is cut off and becomes single phase induction motors.
The power of this kind of electric motor is 120W~3700W.
3、Capacitor running type single phase motor
The stator winding of this kind of motor is also two sets of winding, and the structure is basically the same, but the technical index of the capacitor-run motor is better than other forms of motor.
Although it has better running performance, the starting performance is poor, i.e. the starting torque is low, and the larger the capacity of the motor, the smaller the ratio of starting torque to rated torque.
Therefore, the capacity of capacitor-run motors is not large, generally less than 180W.
4、Single-phase capacitor starting and running single phase motor
This kind of single phase motor accesses two capacitors in the secondary winding, one of them is cut off after starting through the centrifugal switch; the other one is always involved in the work of the secondary winding.
Of these two capacitors, the starting capacitor has a large capacity, while the running capacitor has a small capacity.
This kind of single-phase capacitor starting and running motor integrates the advantages of single-phase capacitor starting and capacitor running motor.
So this kind of single phase motor has better starting performance and running performance, and the power can be increased by 1 to 2 capacity levels in the same seat number, and the power can reach 0.75 kW to 7.5kW.
5、Single-phase shaded-pole type single phase motor
It is an asynchronous motor with simple structure, generally with convex pole stator, the main winding is a centralized winding, while the secondary phase winding is a single-turn short-circuit ring, called shaded grade coil.
The performance of this kind of single phase motor is poor, but because of the solid structure and cheap price, the production quantity of this kind of motor is still large, but the output power is usually not more than 20W.
2. Working principle of single phase motors
In the AC motors, when the stator winding passes through the AC current, the armature magnetomotive force is established, which has a great influence on the energy conversion and operating performance of the single phase induction motors.
So the single-phase AC winding is passed into the single-phase AC to produce a pulsating magnetic potential, which can be decomposed into two rotating magnetic potentials of equal amplitude and opposite speed, thus establishing a forward and reverse magnetic field and in the air gap.
These two rotating magnetic fields cut the rotor conductor and generate the induced electric potential and induced current in the rotor conductor, respectively.
This current interacts with the magnetic field to produce the forward and reverse electromagnetic torque.
The forward electromagnetic torque attempts to make the rotor rotate forward; the reverse electromagnetic torque attempts to make the rotor rotate backward.
The superposition of these two torques is the synthetic torque that drives the single phase induction motor rotation.
3. Structural characteristics and usage of single phase induction motor
The basic characteristics of asynchronous motor are that the rotor winding does not need to be connected to other power sources, and its stator current is taken directly from the AC single phase supply power system; compared with other three phase motors, the structure of asynchronous motor is simple, easy to manufacture, use and maintain, with high operational reliability, light weight and low cost.
Single-phase asynchronous motor is small in single phase power and mainly made into small electric motors.
It has a wide range of applications, such as household appliances (washing machines, refrigerators, electric fans), power tools (such as hand drills), medical equipment, automation instruments, etc.
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