1. Efficiency and power factor

When the asynchronous motor is working, the rotor winding must absorb part of the electric energy excitation from the grid, which consumes the grid energy. This part of the electric energy is finally consumed by the current in the rotor winding. This loss accounts for about 20~30% of the total loss of the motor. The efficiency of the motor is reduced. After the rotor excitation current is converted to the stator winding, it becomes an inductive current, so that the current entering the stator winding lags behind the grid voltage by an angle, causing the power factor of the motor to decrease.

In addition, from the efficiency and power factor curves of permanent magnet synchronous motors and asynchronous motors (Figure 1), it can be seen that when the load rate (=P2/Pn) of the asynchronous motor is less than 50%, its operating efficiency and operating power factor will drop significantly. , So it is generally required to operate in the economic zone, that is, the load rate is between 75%-100%.

After the permanent magnet is embedded in the rotor of the permanent magnet synchronous motor, the permanent magnet establishes the rotor magnetic field. During normal operation, the rotor and the stator magnetic field operate synchronously. There is no induced current in the rotor, and there is no rotor resistance loss. Only this item can improve The motor efficiency is 4%~50%. Since there is no induced current excitation in the rotor of the hydromagnetic motor, the stator winding may be a pure resistive load, making the power factor of the motor close to one infinitely. From the efficiency and power factor curves of the permanent magnet synchronous motor and the asynchronous motor (Figure 1), it can be seen that when the load rate of the permanent magnet synchronous motor is >20%, its operating efficiency and operating power factor will not change much, and the operating efficiency >80%.

2. Working temperature rise

When the asynchronous motor is working, the rotor winding has current flowing, and this current is completely consumed in the form of heat energy, so a large amount of heat will be generated in the rotor winding, which will increase the temperature of the motor and affect the service life of the motor.

Due to the high efficiency of the permanent magnet motor, there is no resistance loss in the rotor winding, and there is little or almost no reactive current in the stator winding, so that the temperature rise of the motor is low. The extremely low temperature rise also ensures the life of the permanent magnet and extends The service life of the motor, and the full application of the elevator traction machine also proves this point.

3. Impact on grid operation

Due to the low power factor of the asynchronous motor, the motor has to absorb a large amount of reactive current from the power grid, causing a large amount of reactive current in the power grid, power transmission and transformation equipment, and power generation equipment. The load of substation equipment and power generation equipment, and the reactive current in the power grid, power transmission and transformation equipment and power generation equipment will consume part of the electric energy, resulting in lower efficiency of the power grid, which affects the effective use of electric energy. Also due to the low efficiency of asynchronous motors, to meet the requirements of output power, it is necessary to absorb more electrical energy from the grid, which further increases the loss of electrical energy and increases the load on the grid.

There is no induced current excitation in the permanent magnet motor rotor, and the power factor of the motor is high, which improves the quality factor of the power grid and eliminates the need to install a compensator in the power grid. At the same time, due to the high efficiency of the permanent magnet motor, it also saves electrical energy

4. Energy saving calculation

When the efficiency of a motor under the rated load is increased from η1 to η2, the electric energy ws (kW•h) saved by the motor running for one year is as follows: where: PN----motor rated power (kW); LF%-motor operating load rate; Th-annual operating time (h).

Taking 22kW-4P motor rated operating conditions as an example, the efficiency of Y series asynchronous motors is 91.5%. When the efficiency is increased to 94.7% after changing to a high-efficiency permanent magnet motor, the unit will save electricity every year: 4.09x103 kW.h

Note: The above calculations are performed under rated conditions. If the load rate changes and the speed range is wide, the energy-saving effect is far greater than the rated point.

5. Summary

Compared with the asynchronous motor, the permanent magnet synchronous motor has obvious advantages. It has high efficiency, high power factor, good performance index, small size, light weight, low temperature rise, significant technical effect, and better improvement of the quality factor of the power grid. , It gives full play to the capacity of the existing power grid and saves the investment in the power grid. It greatly solves the phenomenon of "big horse-drawn carts" in electrical equipment. The TYCP series rare earth permanent magnet variable frequency speed regulating motor produced by Wuxi Xinli Electric Co., Ltd. is an ideal power choice for high-efficiency and energy-saving air compressors.