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. has compiled some relevant information to share with us, in the hope that it will be of some use for practical work.
Fans and pumps are loaded
Fans, water pumps, oil pumps and other equipment with the rolling of the impeller, with the decrease of speed, the torque decreases according to the square 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 by adjusting the speed, which can greatly save electricity. Because the required power increases 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 speed, due to the restriction of 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 is always stable or substantially stable at any speed. When the inverter drags a load of constant torque nature, the torque at low speed should be large enough and have sufficient overload capacity. 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 due to excessive temperature rise.
Problems that should be paid attention to when selecting inverters
1. The current value of the motor is used as the basis for the selection of the inverter, and the additional power of the motor is only for reference.
2. Compared with ordinary squirrel cage motors, the winding motor simply presents the problem of overcurrent tripping, and the inverter with a slightly larger capacity than the general capacity should be selected.
3. 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%.
4. When the frequency converter is used to drive the gear reducer motor, the application range is constrained by the smooth way of the gear rolling part. When the extra revs are exceeded, the danger of running out of oil can occur.
5. Special occasions such as high temperature, frequent switching, high altitude and so on will make the capacity of the inverter drop rain, and it is recommended that the inverter be selected according to the magnification level.
6. The output of the inverter contains abundant high-order harmonics, which will reduce the power factor and power function of the motor.
7. 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 magnified by one or two gears.
8. For loads with large torque fluctuations such as compressors and vibrating machines and peak loads such as hydraulic pumps, we should fully understand the power frequency operation status and select a larger inverter.
9. Compared with the power frequency power supply, the output capacity of the inverter will decrease by 10-20% when driving the synchronous motor.
10. When using the inverter to control the high-speed motor, more high-order harmonics will occur. 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 ordinary motor.
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