The difference between ordinary and variable frequency motors
Release time:
2021-03-03 17:12
First of all, ordinary motors cannot be used as variable frequency motors.
Ordinary motors are designed according to constant frequency and constant voltage, and cannot fully adapt to the speed regulation requirements of the inverter, so they cannot be used as variable frequency motors.
1. The impact of the frequency converter on the motor is mainly on the efficiency and temperature rise of the motor.
The frequency converter can produce varying degrees of harmonic voltages and currents during operation, causing the motor to operate under non-sinusoidal voltages and currents. The high-order harmonics inside will cause an increase in the stator copper loss, rotor copper loss, iron loss and additional losses of the motor. , the most significant is the rotor copper loss. These losses will cause the motor to generate additional heat, reduce efficiency, and reduce output power. The temperature rise of ordinary motors generally increases by 10%-20%.
Ordinary motor Variable frequency motor with independent cooling fan
2. The problem of insulation strength of electric motor
The carrier frequency of the frequency converter ranges from several thousand to more than ten kilohertz, which causes the motor stator winding to withstand a very high voltage rise rate, which is equivalent to applying a steep impact voltage to the motor, putting the motor's inter-turn insulation under severe test. .
3. Harmonic electromagnetic noise and vibration
When ordinary motors are powered by frequency converters, the vibration and noise caused by electromagnetic, mechanical, ventilation and other factors will become more complicated. The various harmonics contained in the variable frequency power supply interfere with the inherent spatial harmonics of the electromagnetic part of the motor, forming various electromagnetic excitation forces, thereby increasing the noise. Since the motor has a wide operating frequency range and a large rotational speed variation range, it is difficult for the frequencies of various electromagnetic force waves to avoid the natural vibration frequencies of the various structural parts of the motor.
4. Cooling issues at low speeds
When the power supply frequency is low, the losses caused by higher harmonics in the power supply are greater; secondly, when the motor speed is reduced, the cooling air volume decreases in proportion to the cube of the speed, resulting in the motor heat being unable to dissipate and the temperature rising sharply. increase, it is difficult to achieve constant torque output.
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