Can ordinary motors be used as variable frequency motors?

2021-10-18 13:32:38 jact_elec

Can ordinary motors be used as variable frequency motors?Ordinary motors are designed according to constant frequency and constant voltage, which cannot fully meet the requirements of frequency converter speed regulation, so they cannot be used as frequency conversion motors.

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◆The influence of the frequency converter on the motor is mainly in the efficiency and temperature rise of the motor

The frequency converter can generate different levels of harmonic voltage and current during operation, so that the motor runs under non-sinusoidal voltage and current. The higher harmonics inside will cause the motor stator copper loss, rotor copper loss, iron loss and additional loss to increase The most significant is the copper loss of the rotor. 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%.

◆The insulation strength of the motor

The carrier frequency of the inverter is from several thousand to ten thousand Hz, which makes the stator winding of the motor to withstand a high rate of voltage rise, which is equivalent to imposing a steep impulse voltage on the motor, which makes the inter-turn insulation of the motor bear more serious tests .

◆Harmonic electromagnetic noise and vibration

When an ordinary motor is powered by a frequency converter, the vibration and noise caused by electromagnetic, mechanical, ventilation and other factors will become more complicated. The harmonics contained in the variable frequency power supply interfere with the inherent spatial harmonics of the electromagnetic part of the motor to form various electromagnetic excitation forces, thereby increasing noise.

Due to the wide operating frequency range of the motor and the wide range of rotation speed, the frequency of various electromagnetic force waves is difficult to avoid the natural vibration frequency of the various structural parts of the motor.

◆Cooling problem at low speed

When the frequency of the power supply is low, the loss caused by the higher harmonics in the power supply is large; secondly, when the speed of the flexible motor is reduced, the cooling air volume decreases in proportion to the third power of the speed, which causes the motor heat to not be dissipated and the temperature rises sharply. Increase, it is difficult to achieve constant torque output.