The Working Principle And Characteristics Of Single-phase Asynchronous Motor

Single-phase asynchronous motors only need single-phase alternating current, so they are easy to use, widely used, and have the advantages of simple structure, low cost, low noise, and little interference to radio systems, so they are often used in household appliances and small power machinery with low power. .

Our domestic single-phase voltage is 220V, while foreign single-phase voltage is different from ours, eg: 120V in the United States, 100V in Japan, 230V in Germany, Britain and France, etc. Therefore, when using foreign single-phase asynchronous motors, it is necessary to pay attention to whether the rated voltage of the motor is the same as the power supply voltage.

The single-phase AC winding is connected to the single-phase AC to generate a pulsed magnetomotive force, which can be decomposed into two rotating magnetomotive force sums with equal amplitudes and opposite rotation speeds, thereby establishing forward and reverse magnetic fields and sums in the air gap. . These two rotating magnetic fields cut the rotor conductor and generate induced electromotive force and induced current in the rotor conductor, respectively.

The interaction between the current and the magnetic field produces positive and negative electromagnetic torques. Forward electromagnetic torque attempts to make the rotor rotate forward; reverse electromagnetic torque attempts to reverse the rotor. The superposition of these two torques is the resultant torque that drives the motor to rotate.

Regardless of whether it is a forward rotating magnetic field or a reverse rotating magnetic field, the relationship between their magnitude and slip is the same as that of a three-phase asynchronous motor. If the speed of the motor is n, for the forward magnetic field, the slip is: s+=(n1-n)/n1=s. For the reverse magnetic field, the slip is: s-=(-n1-n)/-n1=s.

The main features of single-phase asynchronous motors are:

1. n=0, s=1, T=T++ T- =0, indicating that the single-phase asynchronous motor has no starting torque. If no other measures are taken, the motor cannot be started.

2. When s≠1, T≠0, T has no fixed direction, it depends on the positive and negative of s.

3. Due to the existence of the reverse torque, the combined torque is also reduced, so the overload capacity of the single-phase asynchronous motor is low.

The working principle of capacitor split-phase starting

When starting, the switch K is closed, so that the phase difference between the two winding currents I1 and I2 is about 90°, thereby generating a rotating magnetic field, and the motor rotates; after the rotation is normal, the centrifugal switch is thrown away, and the starting winding is cut off.

The working principle of the shaded pole single-phase motor

After the stator is fed with current, part of the magnetic flux passes through the short-circuit ring and induces current in it. The current in the short-circuit ring hinders the change of the magnetic flux, resulting in a phase difference between the magnetic flux generated by the part with the short-circuit ring and the part without the short-circuit ring, thereby forming a rotating magnetic field and making the rotor rotate.

Before the motor is installed, the insulation resistance of the stator winding to the casing and the main winding and the auxiliary winding should be measured, and the resistance at room temperature should not be less than 10MΩ. Otherwise, the winding should be dried, and the bulb heating method can be used.

The shaft extension diameter of the motor has been ground to the standard tolerance size when leaving the factory, so it is required that the inner diameter of the pulley or other supporting parts provided by the user should choose the national standard accessories. When installing, just push in by hand or tap lightly on the shaft extension. It is strictly forbidden to hit it with a hammer, otherwise it will easily break the centrifugal switch, which will cause the motor to fail to start, damage the bearing and increase the running noise of the motor.

Before installing the motor to the supporting machinery, carefully check the foot part of the motor for cracks and problems such as affecting the mechanical strength. Once any problems are found, installation and use are prohibited. The motor should be installed on a flat plate with fixing holes and fixed with bolts suitable for the foot holes. To ensure safety, before the motor runs, be sure to connect the grounding wire to the grounding screw of the motor and ground it reliably. The grounding wire should be a copper wire with a cross-sectional area of not less than 1m㎡.