What Are The Classification Of Synchronous Motors?

Definition: Synchronous motor is a common AC motor like induction motor.

Features: During steady-state operation, there is a constant relationship between the rotor speed and the grid frequency n = ns = 60f / p, and ns becomes the synchronous speed. If the frequency of the power grid does not change, the speed of the synchronous motor in the steady state is constant regardless of the size of the load.

Division: Synchronous motors are divided into synchronous generators and synchronous motors. The AC machines in modern power plants are mainly synchronous motors.

Working principle: the establishment of the main magnetic field: the excitation winding is connected with a DC excitation current to establish an excitation magnetic field between polarities, that is, a main magnetic field is established. Current-carrying conductor: The three-phase symmetrical armature winding acts as a power winding and becomes a carrier of induced electric potential or induced current. Cutting motion: The prime mover drags the rotor to rotate (inputting mechanical energy to the motor), and the excitation magnetic field between the polarities rotates with the shaft and sequentially cuts the stator phase windings (equivalent to the winding conductor cutting the excitation magnetic field in reverse). Generation of alternating electric potential: Due to the relative cutting movement between the armature winding and the main magnetic field, a three-phase symmetrical alternating electric potential with periodically varying magnitude and direction will be induced in the armature winding. AC power can be provided through the lead-out cable. Alternation and symmetry: Because the polarities of the rotating magnetic field are alternated, the polarity of the induced potential alternates; due to the symmetry of the armature winding, the three-phase symmetry of the induced potential is ensured.

1. AC synchronous motor

AC synchronous motor is a constant speed drive motor. Its rotor speed and power frequency maintain a constant proportional relationship. It is widely used in electronic instruments, modern office equipment, textile machinery and so on.

2. Permanent magnet synchronous motor

Permanent magnet synchronous motor belongs to asynchronous start permanent magnet synchronous motor. Its magnetic field system is composed of one or more permanent magnets, usually inside the cage rotor welded by cast aluminum or copper bar, installed according to the required number of poles Magnetic poles inlaid with permanent magnets. The stator structure is similar to the asynchronous motor.

When the stator winding is connected to the power supply, the motor starts to rotate based on the asynchronous motor principle and accelerates to synchronous speed. The synchronous electromagnetic torque generated by the rotor permanent magnetic field and the stator magnetic field (the electromagnetic torque generated by the rotor permanent magnetic field is The reluctance torque generated by the stator magnetic field) pulls the rotor into synchronization, and the motor enters synchronous operation.

Reluctance Synchronous Motor Reluctance Synchronous Motor is also called reactive synchronous motor. It is a synchronous motor that uses reluctance between rotor cross-axis and straight axis to generate reluctance torque. Its stator structure is similar to that of asynchronous motor, but the rotor structure different.

3. Reluctance Synchronous Motor

The evolution of the same cage type asynchronous motor, in order to make the motor can produce asynchronous starting torque, the rotor is also equipped with cage cast aluminum winding resistance. The rotor is provided with a reaction slot corresponding to the number of stator poles (only the role of salient poles, without excitation winding and permanent magnet), which is used to generate reluctance synchronous torque. According to the structure of the reaction tank on the rotor, it can be divided into an inner reactive rotor, an outer reactive rotor and an inner and outer reactive rotor. Among them, the outer reactive rotor reaction tank opens the outer circle of the rotor so that the straight axis and the cross axis direction The air gap varies. The inner reactive rotor has grooves inside, which hinders the magnetic flux in the direction of the cross axis and increases the magnetic resistance. The internal and external reactive rotor combines the structural characteristics of the above two rotors. The difference between the straight shaft and the cross shaft is large, so that the power of the motor is large. Reluctance synchronous motors are also divided into single-phase capacitor running type, single-phase capacitor starting type, single-phase dual-value capacitor type and other types.

4. Hysteresis Synchronous Motor

Hysteresis synchronous motors are synchronous motors that use hysteresis materials to generate hysteresis torque and operate. It is divided into inner rotor type hysteresis synchronous motor, outer rotor type hysteresis synchronous motor and single-phase hood pole type hysteresis synchronous motor.

The rotor structure of the internal rotor hysteresis synchronous motor is a hidden pole type, with a smooth cylindrical appearance. There is no winding on the rotor, but there is an annular effective layer made of hysteresis material on the outer circle of the core.

After the stator winding is connected to the power supply, the generated rotating magnetic field causes the hysteresis rotor to generate asynchronous torque and start to rotate, and then it is automatically pulled into the synchronous operation state. When the motor runs asynchronously, the rotating magnetic field of the stator repetitively magnetizes the rotor at the slip frequency; during synchronous operation, the hysteresis material on the rotor is magnetized and permanent magnet poles appear, resulting in synchronous torque. The soft starter uses three opposite parallel thyristors as the voltage regulator, which is connected between the power supply and the motor stator. Such a circuit is a three-phase fully controlled bridge rectifier circuit. When a soft starter is used to start the motor, the output voltage of the thyristor gradually increases, and the motor gradually accelerates until the thyristor is fully turned on. The motor works on the mechanical characteristics of the rated voltage to achieve smooth start, reduce the starting current, and avoid starting overcurrent trip. When the motor reaches the rated speed, the starting process ends, and the soft starter automatically replaces the completed thyristor with a bypass contactor to provide rated voltage for the normal operation of the motor to reduce the thermal loss of the thyristor and extend the service life of the soft starter , Improve its work efficiency, and make the grid avoid harmonic pollution. The soft starter also provides a soft stop function. In contrast to the soft start process, the soft stop gradually reduces the voltage and the number of revolutions gradually drops to zero to avoid the torque shock caused by free stop.