Working principle of electric tools

Electric motors can be divided into DC motors and AC motors due to different input currents:

(1) DC motor - A motor that uses DC current to rotate is called a DC motor. Due to the different ways in which the magnetic field circuit is connected to the armature circuit, it can also be divided into series excited motors, split excited motors, and compound excited motors;

(2) AC motor - An induction motor in an AC motor, in which the strong induced current (eddy current) is generated in a rotating magnetic field. The copper rod on the rotor continuously cuts the magnetic line of force. According to Lenz's law, this induced current has the effect of resisting relative motion between the magnetic field and the rotor, so the rotor rotates with the magnetic field. However, the rotational speed of this rotor is not as high as the speed of magnetic field transformation, otherwise the magnetic field lines will not be cut by the copper rod.

An electric motor that rotates with alternating current is called an alternating current motor. There are many types, mainly including:

a. Rectifier motor - a series excited DC generator used as an AC motor, which is a type of motor. Due to the simultaneous rotation of AC current in the magnetic field and armature circuit, the direction of the couple moment remains constant, and the machine does not stop rotating. This type of motor is also known as a "universal motor" because it can use both AC and DC. This type of motor is commonly used in vacuum cleaners, sewing machines, and other household appliances.

b. Induction motor - a device that places the rotor in a rotating magnetic field and causes the rotor to rotate due to the action of eddy current. The rotating magnetic field is not caused by mechanical methods, but rather by alternating current flowing through several pairs of electromagnets, causing cyclic changes in their magnetic polarity, which can be regarded as a rotating magnetic field. Usually, three-phase induction motors (with three pairs of magnetic poles) are used. The motion of a DC motor is exactly opposite to that of a DC generator, where the induced current is formed by the induced electromotive force, so they are in the same direction. In an electric motor, the direction of the induced electromotive force supplied by an external power source is opposite to the direction of the armature current I.

c. Synchronous motor - a motor whose armature rotates from one pole to the next, exactly in the same cycle as the rotation of the incoming current. This type of motor cannot be started on its own, and another motor or special auxiliary winding must be used to reach the appropriate frequency before AC power can be connected. If the load changes and the speed changes, the speed will not match the AC frequency, which is enough to cause disorder in its pace, tend to stop or cause damage. Due to many limitations, it is not widely used.