It has become an irreversible trend to drive the motor through the inverter, and in the actual application process, because the matching relationship between the inverter and the motor is not very reasonable, it often leads to some problems. When selecting an inverter, you should fully understand the load characteristics of the equipment driven by the inverter. Ms. Shen has compiled some relevant materials to share with you, in the hope that they will be useful for practical assignments.
Fans and pumps are loaded
With the rolling of the impeller, the fan, water pump, oil pump and other equipment decreases according to the square of the speed with the decrease of the speed, and the power required by the load is proportional to the third power of the speed. When the required air volume and flow rate are reduced, the inverter can be used to adjust the air volume and flow rate through speed regulation, which can greatly save electricity. Because the required power is added too quickly with the speed at high speed, the fan and pump load should not be operated beyond the power frequency.
Constant power load
The torque required for the spindle of the machine tool and the coiler and uncoiler in the rolling mill, paper machine, and plastic film production line is roughly inversely proportional to the rotational speed and belongs to the constant power load. The constant power nature of the load should be in terms of a certain range of speed changes. When the speed is very low, it will change to a constant torque load at low speeds, limited by the mechanical strength. When the motor adjusts the speed with constant magnetic flux, it regulates the speed of constant torque; In the case of weak magnetic speed regulation, it is constant power speed regulation.
Constant torque load
TL always sticks stable or basically stable at any speed. When the inverter drags a load of constant torque nature, the torque at low speed should be large enough and there should be enough overload. If you need to run at a steady speed at low speed, you should consider the heat dissipation function of the motor to prevent the motor from burning out due to excessive temperature rise.
Problems that should be paid attention to when selecting inverters
● The current value of the motor is used as the basis for the selection of the inverter, and the rated power of the motor is only for reference.
● Compared with the general squirrel cage motor, the winding motor is prone to overcurrent tripping problem, and the inverter with a slightly larger capacity than the general capacity should be selected.
● When the power frequency motor is dragged by the inverter, the current of the motor will increase by 10-15%, and the temperature rise will increase by about 20-25%.
● When the inverter is used to drive the gear reducer motor, the application range is limited by the lubrication method of the gear rolling part. When the rated speed is exceeded, there is a risk of running out of oil.
●High temperature, frequent switching, high altitude and other special occasions will make the capacity of the inverter drop rain, it is recommended that the inverter be selected according to the expansion of one gear.
● The output of the inverter is rich in high-order harmonics, which will reduce the power factor and efficiency function of the motor.
● When the inverter wants to run with a long cable, the influence of the cable on the function should be considered, and a special cable should be selected if necessary. To compensate for this problem, the inverter should be expanded by one or two gears.
●For loads with large torque fluctuations such as compressors and vibrating machines, and peak loads such as hydraulic pumps, it is necessary to fully understand the power frequency operation status and select a larger inverter.
●Compared with the power frequency power supply, the output capacity of the inverter will be reduced by 10-20% when driving the synchronous motor.
● When the inverter is used to control the high-speed motor, more high-order harmonics will be generated. These higher harmonics will increase the output current value of the inverter. Therefore, when selecting the inverter, it should be one gear larger than the general motor.
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