8 synchronous motor
Synchronous motors, like induction motors, are a common AC motor. The characteristic is: in 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 grid is constant, the speed of the synchronous motor at steady state is constant and independent of the magnitude of the load. Synchronous motors are classified into synchronous generators and synchronous motors. The AC machine in modern power plants is dominated by synchronous motors.
working principle
The establishment of the main magnetic field: the excitation winding is connected to the DC excitation current to establish the excitation magnetic field between the polar phases, that is, the main magnetic field is established.
Current-carrying conductor: A three-phase symmetrical armature winding acts as a power winding and acts as a carrier for inductive or induced current.
Cutting motion: The prime mover drags the rotor to rotate (the mechanical energy is input to the motor), and the excitation magnetic field between the polar phases rotates with the shaft and sequentially cuts the stator phase windings (corresponding to the conductors of the windings to cut the excitation magnetic field).
Generation of alternating potential: Due to the relative cutting motion between the armature winding and the main magnetic field, a three-phase symmetric alternating potential whose magnitude and direction change periodically will be induced in the armature winding. AC power is available through the lead wires.
Cross-change and symmetry: Due to the polarity of the rotating magnetic field, the polarity of the induced potential is alternating; due to the symmetry of the armature winding, the three-phase symmetry of the induced potential is guaranteed. [1]
First, AC synchronous motor
AC synchronous motor is a constant speed drive motor. Its rotor speed is kept constant with the power frequency. It is widely used in electronic instrumentation, modern office equipment, textile machinery and so on.
Second, permanent magnet synchronous motor
A permanent magnet synchronous motor is an asynchronous start permanent magnet synchronous motor whose magnetic field system consists of one or more permanent magnets, usually inside a cage rotor welded with cast aluminum or copper strips, in the required number of poles. A magnetic pole with permanent magnets. The stator structure is similar to an asynchronous motor.
When the stator winding is connected to the power supply, the motor starts to rotate according to the principle of the asynchronous motor, and when the synchronous operation is accelerated to the synchronous speed, the synchronous electromagnetic torque generated by the permanent magnet magnetic field of the rotor and the stator magnetic field (the electromagnetic torque generated by the permanent magnet magnetic field of the rotor The reluctance torque generated by the stator magnetic field is combined to drive the rotor into synchronization, and the motor enters synchronous operation.
Reluctance Synchronous Motor Reluctance Synchronous Motor, also called reactive synchronous motor, is a synchronous motor that generates reluctance torque by using the rotor axis and the direct axis reluctance. The stator and the asynchronous motor have similar stator structures, but the rotor structure. different.
Third, the reluctance synchronous motor
In the same cage type asynchronous motor, in order to make the motor generate asynchronous starting torque, the rotor is also provided with a cage cast aluminum winding. A reaction tank corresponding to the number of poles of the stator (only the action of the salient pole portion, the non-excited winding and the permanent magnet) is opened on the rotor for generating the reluctance synchronous torque. According to the structure of the reaction tank on the rotor, it can be divided into an inner reaction type rotor, an outer reaction type rotor and an inner and outer reaction type rotor. The outer reaction type rotor reaction groove opens the outer circumference of the rotor to make the direct axis and the intersecting axis direction. Air gaps are not equal. The inner portion of the inner reaction type rotor is grooved, so that the magnetic flux in the cross-axis direction is blocked and the magnetic resistance is increased. The internal and external reactive rotors combine the structural characteristics of the above two types of rotors, and the difference between the straight axis and the intersecting axis is large, so that the force energy of the motor is large. Magnetoresistive synchronous motors are also classified into single-phase capacitor operation type, single-phase capacitor start type, and single-phase double-value capacitor type.
Fourth, hysteresis synchronous motor
A hysteresis synchronous motor is a synchronous motor that operates with a hysteresis material to generate hysteresis torque. It is divided into an inner rotor type hysteresis synchronous motor, an outer rotor type hysteresis synchronous motor and a single-phase shaded hysteresis synchronous motor.
The rotor structure of the inner rotor type hysteresis synchronous motor is a hidden pole type, and the appearance is a smooth cylinder. There is no winding on the rotor, but an annular effective layer made of a hysteresis material is used on the outer circumference of the core.
After the stator winding is turned on, the generated rotating magnetic field causes the hysteresis rotor to generate asynchronous torque to start the rotation, and then pulls into the synchronous operation state by itself. When the motor is running asynchronously, the rotating magnetic field of the stator repeatedly magnetizes the rotor at a slip frequency; during synchronous operation, the hysteresis material on the rotor is magnetized to produce a permanent magnet pole, thereby generating a synchronous torque. The soft starter uses three opposite-parallel thyristors as regulators, which are connected between the power supply and the stator of the motor. Such a circuit is a three-phase fully controlled bridge rectifier circuit. When the motor is started by the soft starter, the output voltage of the thyristor is gradually increased, and the motor is gradually accelerated until the thyristor is fully turned on. The motor operates on the mechanical characteristic of the rated voltage to achieve a smooth start, reduce the starting current, and avoid starting the overcurrent trip. When the motor reaches the rated number of revolutions, the start-up process ends. The soft starter automatically replaces the completed thyristor with a bypass contactor to provide a rated voltage for the normal operation of the motor to reduce the heat loss of the thyristor and prolong the service life of the soft starter. To improve the efficiency of its work, and to avoid harmonic pollution in the power grid. The soft starter also provides a soft stop function. The soft stop is opposite to the soft start process. The voltage gradually decreases and the number of revolutions gradually decreases to zero, avoiding the torque shock caused by free parking.
