Specification for type selection of the hottest ge

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General inverter selection specification

the correct selection of inverter is very critical for the normal operation of the control system. When selecting a frequency converter, you must fully understand the load characteristics driven by the frequency converter. In practice, people often divide the production machinery into three types, because the electromagnetic type is driven by the principle of electromagnetic resonance: constant torque load, constant power load, fan and water pump load

constant torque load:

load torque TL has nothing to do with speed n, and TL always remains constant or basically constant at any speed. For example, friction loads such as conveyor belts, mixers, extruders, and potential loads such as cranes and hoists belong to constant torque loads

when the frequency converter drives a load with constant torque, the torque at low speed should be large enough and have enough overload capacity. If it is necessary to operate at a steady speed at a low speed, the heat dissipation capacity of the standard asynchronous motor should be considered to avoid excessive temperature rise of the motivation, said Jos bastiaens, European technology and innovation manager

constant power load:

the torque required by the machine spindle and the coiler and uncoiler in the rolling mill, paper machine and plastic film production line is generally inversely proportional to the speed, which is the so-called constant power load. The constant power property of the load should be in terms of a certain speed variation range. When the speed is very low, TL cannot increase infinitely due to the limitation of mechanical strength, and changes to constant torque at low speed. The constant power area and constant torque area of the load have a great influence on the selection of the transmission scheme. When the motor is in constant flux speed regulation, the maximum allowable output torque remains unchanged, which belongs to constant torque speed regulation; In the field weakening speed regulation, the maximum allowable output torque is inversely proportional to the speed, which belongs to constant power speed regulation. If the range of constant torque and constant power speed regulation of the motor is consistent with the range of constant torque and constant power of the load, that is, under the so-called "matching" condition, the capacity of the motor and the capacity of the frequency converter are the smallest

fan and pump loads:

in various fans, water pumps and oil pumps, with the rotation of the impeller, the resistance generated by air or liquid within a certain speed range is roughly proportional to the power of speed n. As the speed decreases, the speed decreases to the power of the speed. The power required by this load is proportional to the third power of speed. When the required air volume and flow are reduced, using the frequency converter to adjust the air volume and flow through the speed regulation mode of

can greatly save electric energy. As the power required at high speed increases too fast with the speed, which is proportional to the third power of the speed, it is usually not necessary to make the fan and pump load operate at more than power frequency

Siemens can provide different types of frequency converters, and users can choose different types of frequency converters according to their actual process requirements and application occasions. Pay attention to the following precautions when selecting frequency converters:

1. Select frequency converters according to load characteristics. If the load is constant torque load, Siemens MMV/MDV frequency converters should be selected. If the load is fan and pump load, Siemens eco should be selected. Many high consumption, low efficiency and other mechanical products in the market are gradually eliminated

2. when selecting the frequency converter, the actual motor current value should be used as the basis for selecting the frequency converter, and the rated power of the motor can only be used as a reference. In addition, it should be fully considered that the output of the frequency converter contains high-order harmonics, which will cause the power factor and efficiency of the motor to deteriorate. Therefore, compared with the power supply of power frequency, the current of the motor increased by 10% and the temperature rise increased by about 20%. Therefore, when selecting motor and frequency converter, this situation should be taken into account, and appropriate allowance should be left to prevent excessive temperature rise from affecting the service life of the motor

3. if the frequency converter wants to run with a long cable, measures should be taken to suppress the influence of the long cable on the ground coupling capacitance to avoid insufficient output of the frequency converter. Therefore, the frequency converter should enlarge the first gear selection or install the output reactor at the output end of the frequency converter

4. When the frequency converter is used to control several motors in parallel, it must be considered that the total length of the cable from the frequency converter to the motor is within the allowable range of the frequency converter. If the specified value is exceeded, the frequency converter shall be selected by amplifying the first gear or the second gear. In addition, in this case, the control mode of the frequency converter can only be v/F control mode, and the frequency converter cannot protect the overcurrent and overload protection of the motor. At this time, it is necessary to add a fuse on each motor to achieve protection

5. for some special applications, such as high ambient temperature, high switching frequency, high altitude, etc., at this time, the capacity of the frequency converter will be reduced, and the frequency converter needs to be amplified for first gear selection

6. when using frequency converter to control high-speed motor, because the reactance of high-speed motor is small, high-order harmonic also increases the output current value. Therefore, when selecting the frequency converter for high-speed motor, it should be slightly larger than that of ordinary motor

7. When the frequency converter is used for pole changing motor, full attention should be paid to the selection of the capacity of the frequency converter so that its maximum rated current is below the rated output current of the frequency converter. In addition, the motor should be stopped before pole number conversion during operation, otherwise the motor will idle and the frequency converter will be damaged in case of bad conditions

8. when driving explosion-proof motor, the frequency converter has no explosion-proof structure, so it should be set outside the dangerous place

9. when using the frequency converter to drive the gear reduction motor, the scope of use is restricted by the lubrication mode of the gear rotating part. When the lubricating oil is lubricated, there is no limit in the low-speed range; In the high-speed range above the rated speed, there may be a danger of running out of lubricating oil. Therefore, do not exceed the allowable maximum speed

10. When the frequency converter drives the wound rotor asynchronous motor, most of them use the existing motor

the winding impedance of wound motor is smaller than that of ordinary squirrel cage motor. Therefore, overcurrent tripping caused by ripple current is easy to occur, so the frequency converter with slightly larger capacity should be selected. Generally, wound motors are mostly used in occasions with large flywheel torque gD2, and more attention should be paid to setting acceleration and deceleration time

11. When the frequency converter drives the synchronous motor, compared with the power frequency power supply, the output capacity is reduced by 10% - 20%, and the continuous output current of the frequency converter is greater than the product of the rated current of the synchronous motor and the unit value of the synchronous pull-in current

12. for loads with large torque fluctuations such as compressors and vibrators and peak loads such as oil pumps, if the frequency converter is selected according to the rated current or power value of the motor, the overcurrent protection action may occur due to the peak current. Therefore, it is necessary to understand the power frequency operation and choose a higher current than its maximum current

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