A frequency converter is a device that converts mains frequency power to power at other frequencies. In China, the power frequency is 50Hz. In the field of motors, many motors use frequency converters to power them in order to change their speed or other performance characteristics.
A frequency converter is a conversion device used in conjunction with a variable frequency motor. In terms of circuit configuration, the frequency converter is positioned between the motor and the mains frequency power supply. Motors with different load characteristics should be matched with frequency converters of different performance.
Relationship between inverter voltage and frequency
Taking an asynchronous motor as an example, the motor's torque is the result of the combined effect of the motor's magnetic flux and rotor current. Taking the rated frequency as the boundary, if the input voltage to the motor remains constant when the power supply frequency is reduced, the motor's magnetic flux will saturate, potentially leading to burnout of the motor windings. Therefore, when reducing the power supply frequency, the motor's input voltage should be reduced simultaneously, with the principle of keeping the motor's magnetic flux constant. This control method is commonly used in loads such as fans and pumps.
For power frequency motors, if the voltage is lower than the rated voltage, the motor current will increase significantly to achieve the same output power, especially for motors running on temporary lines, leading to frequent winding burnouts. Similarly, for motors powered by frequency converters, the increased current also occurs when operating at low speeds to achieve the same output power (constant power operation). However, in constant torque operation, the motor current will not change significantly.
Key control points for testing a 60Hz motor using a 50Hz power supply
Most newly constructed testing facilities are equipped with variable frequency power supplies, allowing testing to be conducted at the actual frequency of the motor. However, some older testing facilities or repair shops may not have the necessary conditions for variable frequency testing. So, how can a 60Hz motor be tested?
According to the theoretical deduction in this article, when using a 50Hz power supply for testing, the voltage should be reduced and the voltage should be applied according to the calculated value of the motor's rated voltage divided by 1.2.
