Nowadays, the application proportion of high efficiency and energy saving motor is low. From the perspective of energy saving and environmental protection, the promotion and application of high efficiency motor has become an irreversible trend.
The loss of three-phase asynchronous motor can be divided into constant loss and load loss. The constant loss includes wind friction loss and iron loss. It is the inherent loss of motor operation, which is related to electrical materials, manufacturing process, structural design, speed and other parameters, and has nothing to do with the size of load. Load loss includes stator copper loss, rotor copper loss and stray loss. For wound rotor motor, it also includes heat loss and electric loss of external circuit.
Core loss. It is composed of eddy current loss and hysteresis loss caused by alternating magnetic field of motor stator winding in iron core. Its size is related to the core material, power frequency and magnetic flux density. The core loss is proportional to the square of the motor voltage.
Air mill loss. Also known as mechanical loss, it is one of the constant losses, mainly including bearing friction loss and ventilation system loss. For wound rotor, there is also brush friction loss. For high efficiency motors, the size of motor fan and the type of bearing seal have a significant impact on the mechanical loss, especially for high speed motors. The larger the motor power, the larger the proportion of mechanical loss in the total loss.
There is a negative correlation between motor efficiency and loss, that is, the higher the efficiency, the smaller the loss. On the contrary, the greater the loss, the lower the efficiency. For high efficiency motor, the effective control of loss is the most effective means to improve the energy efficiency of motor.
When the voltage (but not less than 10%, preferably between 2-3%) is used to ensure the normal operation of the motor, the motor loss should be small; on the contrary, when the operating voltage of the motor is higher than the rated voltage, the motor loss will increase. If the voltage exceeds the rated voltage, the motor current will increase too much, and even lead to burnout. When the motor is no-load, light load and heavy load, the relationship between voltage and efficiency is different.
For the fan pump load, the shaft torque is proportional to the square of the speed. When the frequency is reduced, the speed is reduced, the torque is also reduced, and the stator, stator and rotor currents are reduced. Therefore, the motor efficiency is improved. In addition, the shaft power is greatly reduced, and the motor input power is also greatly reduced. Therefore, the fan pump load adopts the variable frequency speed motor, which can obtain better performance at low speed The energy-saving effect is improved.