What problems are often encountered when using a frequency converter to power a motor?

A frequency converter is a device that converts industrial frequency power into other frequency power. The power frequency in our country is 50Hz. In the field of motors, in order to change the speed of the motor or other performance changes, many motors are powered by frequency converters.

The frequency converter is a conversion device used in conjunction with a variable frequency motor. From the perspective of circuit configuration, the frequency converter is between the motor and the industrial frequency power supply. Motors with different load characteristics should be matched with frequency converters with different performance.

Taking asynchronous motors as an example, the torque of the motor is the result of the interaction between the motor flux and the rotor current. Taking the rated frequency as the boundary, when the frequency of the power supply is reduced, if the input voltage of the motor is kept unchanged, the motor flux will be saturated, and in severe cases, the motor winding will burn out. Therefore, when reducing the power supply frequency, the input voltage of the motor should be reduced at the same time, in order to control the motor flux unchanged. This control method is generally used more on loads such as fans and pumps.

For industrial frequency motors, if the voltage is lower than the rated voltage, the motor current will increase a lot if the same power is to be output, especially for motors running on temporary lines, which will cause a lot of winding burnout. For motors powered by inverters, if the same power is required to be output at low speed, that is, constant power operation, there will also be a problem of increased current. However, if it is a constant torque operation, the motor current will not change much.

Most newly built testing institutions are equipped with variable frequency power supplies, which can perform tests according to the actual frequency of the motor. However, some old testing equipment or some repair units may not have the conditions for variable frequency testing. How to test 60Hz motors?

According to the theoretical inference of this article, when using a 50Hz industrial frequency power supply for testing, the voltage should be reduced and the voltage test should be applied according to the calculated value of the motor rated voltage divided by 1.2.