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Working principle of electric tools

by:WORKSITE     2021-01-06
Due to the different input currents, motors can be divided into DC motors and AC motors:
   (1) DC motor-a motor that uses DC current to rotate is called a DC motor. Due to the different ways of connecting the field circuit and the armature circuit, they can be divided into series motors, split motors, and double motors;
(2) AC motor-the induction motor in the AC motor, its strong induced current (eddy current) is generated in the rotating magnetic field, and the copper rod on the rotor continuously cuts the magnetic field lines. According to Lenz's law, such an induced current There is the effect of opposing the relative movement between the magnetic field and the rotor, so the rotor rotates with the magnetic field. But the rotation speed of this rotor is not as high as that of the magnetic field transformation, otherwise the magnetic lines of force will not be cut by the copper rod.
A motor that uses alternating current to rotate is called an alternating current motor. There are many types, mainly:
a. Rectifier motor-Let the series-excited DC generator be used as an AC motor to form this kind of motor. Since the alternating current is in the magnetic field and the armature circuit, it turns at the same time, so the direction of the couple torque remains unchanged. This machine is Turning non-stop. This kind of motor is also called 'universal motor' because it can use both AC and DC. Vacuum cleaners, sewing machines and other household appliances often use this type of motor.
  B. Induction motor-a device that puts the rotor in a rotating magnetic field and rotates the rotor due to the action of eddy currents. The rotating magnetic field is not created by mechanical methods. Instead, alternating current is passed through several pairs of electromagnets to cyclically change the magnetic pole properties, which can be regarded as a rotating magnetic field. Usually three-phase induction motors (with three pairs of magnetic poles) are used. The movement of a DC motor is just the opposite of that of a DC generator. In the generator, the induced current is formed by the induced electromotive force, so they are in the same direction. In the motor, the current is the direction of the induced electromotive force supplied by the external power source and the direction of the armature current I is opposite.
  C. Synchronous motor-a motor whose armature rotates from one pole to the next pole, exactly at the same cycle as the direction of the current. This kind of motor cannot be started by itself, and another motor or special auxiliary winding must be used to reach the appropriate frequency before it can be connected to the alternating current. If the load changes and the speed changes, the speed will not match the frequency of the alternating current, which will cause its pace to be disordered and tend to stop or cause damage. Due to many restrictions, it is not widely used.
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