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Transfer from three-phase asynchronous motor
What is the classification basis for two common synchronous motors?
The electric excitation synchronous motor and the permanent magnet synchronous motor are classified according to different excitation modes of the synchronous motor.
First, the electric excitation synchronous motor can not be automatically started, so the squirrel cage winding is also installed on the rotor as the motor starting. The squirrel cage windings are placed around the rotor and are similar in construction to asynchronous motors. The rotor is made in an eccentric manner, and the field coils mounted on the pole core are connected in series to each other, and have alternating opposite polarities, and two leads are connected to the two slip rings mounted on the shaft. The field coil is excited by a small DC generator or battery. In most synchronous motors, the DC generator is mounted on the motor shaft to supply the excitation current of the rotor pole coil.
When a three-phase AC power source is connected to the stator winding, a rotating magnetic field is generated in the electric excitation synchronous motor, and the squirrel-cage winding cuts the magnetic line to generate an induced current, thereby rotating the electric excitation synchronous motor. After the electric excitation synchronous motor rotates, its speed gradually increases to a speed slightly lower than the rotating magnetic field. At this time, the rotor field coil is excited by direct current to form a certain magnetic pole on the rotor, and these magnetic poles attempt to track the rotating magnetic pole on the stator. This increases the speed of the motor rotor until it rotates in synchronism with the rotating magnetic field.
Second, permanent magnet synchronous motor: permanent magnet synchronous motor can be applied to single-phase power supply, can also be applied to multi-phase power supply. In this type of motor, one type of stator winding is similar to the stator of a split-phase motor or a multi-phase motor, and has a squirrel-cage rotor, and the surface of the rotor is cut into a plane. Therefore, it belongs to the pole rotor, which is made of a magnetized steel and can always maintain magnetism. The squirrel cage winding is used to generate the starting torque, and when the motor rotates to a certain speed, the rotor pole is synchronized with the current frequency of the stator coil. The polarity of the pole is induced by the stator, so its number should be equal to the number of poles on the stator. When the motor is turned to its proper speed, the squirrel-cage winding loses its function and the rotation is maintained against the rotor. The magnetic poles follow the stator poles to synchronize them.