Rongcheng Motor Manufacturer teaches you how to handle the matching relationship between frequency converters and motors
Driving motors through frequency converters has become an irreversible trend. In actual use, due to the unreasonable matching relationship between frequency converters and motors, some problems often occur. When choosing a frequency converter, one should fully understand the load characteristics of the equipment driven by the frequency converter. Ms. has organized some relevant materials to share with everyone in the hope of being useful for practical work.
We can divide production machinery into three types: constant power load, constant torque load, and fan/pump load. Different load types have different requirements for frequency converters, and we should match them reasonably according to specific situations.
Constant power load
The required torque for machine tool spindles, rolling mills, paper machines, and plastic film production lines such as coilers and uncoiler is generally inversely proportional to the rotational speed and belongs to constant power load. The constant power property of the load should be limited to a certain range of speed changes. When the speed is very low, due to the constraint of mechanical strength, it will change to a constant torque load at low speeds. When the speed of the electric motor is adjusted with constant magnetic flux, it is controlled with constant torque; And in weak magnetic speed regulation, it is constant power speed regulation.
Fan and pump loads
Equipment such as fans, water pumps, and oil pumps rotate with the impeller, and as the speed decreases, the torque decreases by the square of the speed. The power required by the load is directly proportional to the third power of the speed. When the required air volume and flow rate decrease, using a frequency converter to adjust the air volume and flow rate through speed regulation can greatly save electricity. Due to the rapid increase in required power with speed at high speeds, fans and pumps should not be operated beyond power frequency.
Constant torque load
TL always remains constant or essentially constant at any speed. When a frequency converter drives a load with constant torque properties, the torque at low speeds should be sufficiently large and have sufficient overload capacity. If it is necessary to operate steadily at low speeds, the heat dissipation performance of the motor should be considered to avoid burning out due to excessive temperature rise.
Issues to consider when choosing a frequency converter
When a frequency converter is used to drive a power frequency motor, the current of the motor will increase by 10-15%, and the temperature rise will increase by about 20-25%.
When using a frequency converter to control a high-speed motor, a significant amount of high-order harmonics will be generated. And these high-order harmonics will increase the output current value of the frequency converter. Therefore, when choosing a frequency converter, it should be one gear higher than that of a regular electric motor.
Compared with ordinary squirrel cage motors, wound motors are prone to overcurrent tripping problems, and a slightly larger capacity frequency converter should be selected.
When using a frequency converter to drive a gear reduction motor, the range of use is limited by the lubrication method of the rotating parts of the gear. There is a risk of running out of oil when the rated speed is exceeded.
The motor current value is used as the basis for selecting the frequency converter, and the rated power of the motor is only for reference.
The output of the frequency converter contains rich high-order harmonics, which can reduce the power factor and efficiency performance of the motor.
If the frequency converter needs to operate with long cables, the impact of cables on performance should be considered, and if necessary, dedicated cables should be selected. To address this issue, the frequency converter should be enlarged to one or two levels for selection.
In special situations such as high temperature, frequent switching, and high altitude, the capacity of the frequency converter may be affected by rain. It is recommended to select the frequency converter by enlarging it by one level.
Compared with the power supply, when the frequency converter drives the synchronous motor, the output capacity will be reduced by 10-20%.
For loads with large torque fluctuations such as compressors and vibrators, as well as peak loads such as hydraulic pumps, it is necessary to fully understand the power frequency operation and choose a higher frequency converter.
