What is Rare-earth Permanent Magnet Motor
As the name implies, rare-earth permanent magnet motors use rare-earth materials inside the motor. NdFeB rare-earth magnets are embedded in the rotor. The inherent magnetic field of the magnet is used as an excitation source to form a fixed magnetic pole.
When the three-phase stator winding of the motor is fed with three-phase alternating current, a synchronous rotating magnetic field will be generated. According to the principle of magnetic pole homogeneity, repulsion and heterogeneous attraction, the stator rotating magnetic field drives the rotor magnetic pole to rotate, and finally reaches the rotor rotation speed equal to the stator magnetic field rotation speed . Therefore, rare earth permanent magnet motors are also called synchronous motors.
Features Of Rare-Earth Permanent Magnet Motors
The rotor pole of the rare earth permanent magnet motor is composed of rare earth permanent magnet steel, so there is no slip, no excitation current, and the rotor has no fundamental wave iron and copper wear.
The rotor is excited by permanent magnets, and no reactive excitation current is needed. Therefore, the power factor is improved, the reactive power is reduced, the stator current is greatly reduced, and the stator copper and iron losses are greatly reduced.
At the same time, because the polar arc coefficient of the rare earth permanent magnet motor is larger than that of the asynchronous motor, when the voltage and the stator structure are constant, the average magnetic induction intensity of the motor is smaller than that of the asynchronous motor and the iron loss is small.
Therefore, it can be said that the rare earth permanent magnet synchronous motor is energy-saving by reducing its own losses, and is not affected by changes in operating conditions, environment and other factors.
Advantages Of Rare-earth Permanent Magnet Motors
- High efficiency: The efficiency curve of the asynchronous motor generally falls faster under 60% of the rated load, and the efficiency is very low at light load. The efficiency curve of the rare earth permanent magnet motor is high and flat, and it is in the high efficiency area at 20%~120% of the rated load.
- High power factor: The measured value of the power factor of the rare earth permanent magnet synchronous motor is close to the limit value of 1.0. The power factor curve is as high and flat as the efficiency curve. The power factor is high. Low-voltage reactive power compensation is not required and the power distribution system capacity is fully utilized.
- Stator current is small: The rotor has no excitation current, the reactive power is reduced, and the stator current is significantly reduced. Compared with the asynchronous motor of the same capacity, the stator current value can be reduced by 30% to 50%. At the same time, because the stator current is greatly reduced, the motor temperature rise is reduced, and the bearing grease and bearing life are extended.
- High out-of-step torque and pull-in torque: Rare earth permanent magnet synchronous motors have higher out-of-step torque and pull-in torque, which makes the motor have higher load capacity and can be smoothly pulled into synchronization.
Disadvantages Of Rare-earth Permanent Magnet Motors
- High cost: Compared with the asynchronous motor of the same specification, the air gap between the stator and the rotor is smaller, and the processing accuracy of each component is high; the rotor structure is more complicated and the price of rare earth magnetic steel material is high; therefore, the motor manufacturing cost is high, which is common for asynchronous motors About 2 times.
- Large impact at full power start: When starting at full pressure, the synchronous speed can be drawn in a very short time. The mechanical shock is large. The starting current is more than 10 times the rated current. The impact on the power supply system is large, requiring a large capacity of the power supply system.
- Rare-earth magnet steel is easy to demagnetize: When the permanent magnet material is subjected to vibration, high temperature and overload current, its magnetic permeability may decrease, or demagnetization phenomenon occurs, which reduces the performance of the permanent magnet motor.