Both the synchronous machine and the asynchronous machine can rotate, because the stators of these two kinds of motors, the relative movement of electricity and magnetism, can produce the effect of force.
For the synchronous motor, the main magnetic field is mainly the excitation of the The current flows through the excitation winding and is established. The multi-phase symmetrical current flows through the multi-phase symmetrical armature winding, which will generate a rotating magnetic field with a fixed direction. The rotation speed of the rotating magnetic field is determined by the frequency of the current, which also determines The rotation speed of the motor. The rotating magnetic field will drive the rotation of the main magnetic field. When there is an angle between the two magnetic field directions, a stable torque will be output.
For a synchronous generator, the main magnetic field is a separate excitation current flowing through the excitation winding (installed in The external machine drives the motor rotor to rotate at a constant speed, and the main magnetic field also rotates at a certain speed, and its speed is determined by the external mechanical speed. The rotation of the rotating magnetic field is relative to the fixed armature winding movement. The electromotive force is induced in the armature winding. The frequency of the electromotive force is also determined by the external mechanical speed.
The main magnetic field of the synchronous motor is mainly established by the excitation current (the power factor is not less than 1 at this time). When the excitation current is insufficient, the stator current will also be state involved in establishing the main magnetic field, this time will be less than the power factor of the synchronous machine 1, so that the field current can be adjusted to make it work in a leading power factor, a, and lagging behind, the may be used for phase modulation.
induction motor, flowing through the The multi-phase current of the pivot winding generates a rotating magnetic field, which moves relative to the rotor, inducing current in the rotor, generating torque, and causing the rotor to rotate. Since the current in the rotor is generated by induction, there must be a gap between the rotor and the stator. There is relative motion. Therefore, its rotational speed is lower than the speed of the rotating magnetic field established by the armature winding, so it is called asynchronous. Since the main magnetic field needs the current input by the stator to establish, its power factor must be less than 1.
Since the synchronous motor works in a fixed The speed of the synchronous generator is mostly used to drive the load with a fixed speed. The synchronous generator generates a fixed frequency electromotive force, which is mostly used for the generator to facilitate the parallel operation (connection to the grid) of multiple synchronous machines.
Due to the use of the synchronous motor, the comparison of starting It is troublesome and the cost is high. Induction motors are easy to manufacture, easy to maintain, start and control, so for occasions without special requirements, asynchronous motors are often used.