Passfrequency converterdriveMotorIt has become an irreversible trend, and in the actual use process, due to the unreasonable matching relationship between the frequency converter and the motor, it often leads to some problems. When choosing a frequency converter, you should fully understand the load characteristics of the equipment driven by the frequency converter. Ms. Can has compiled some relevant materials to share with you, in order to be useful for practical work.
How to choose a frequency converter after the motor is determined? Is there a uniform formula? The answer is definitely to vary from class to class depending on the load.
1. General principles of matching frequency converters and motors
First of all, look at what load the motor is dragging, if there is a special type, you should choose a special type of frequency converter, if not, choose a general-purpose frequency converter;
Secondly, it is better to look at the rated current of the motor and the output current of the frequency converter, which is slightly larger than the rated current of the motor; For example, the rated current of the motor is 35A, and the 15KW frequency converter can almost meet the requirements of use, but it is best to amplify one gear and choose an 18.5KW frequency converter, which can ensure that the frequency converter is durable.
2. Requirements for different loads to match frequency converters and motors
We can divide production machinery into:constant power load、Constant torque loadandFan and water pump loadsDifferent load types have different requirements for frequency converters, and we should reasonably match them according to the specific situation.
1. Constant power load
The torque required by the machine tool spindle and the winding machine and uncoiler in the rolling mill, paper machine, plastic film production line is generally inversely proportional to the rotation speed, which 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, constrained by mechanical strength. When the motor adjusts the speed of the constant flux, it adjusts the speed for constant torque; while when the weak magnetic speed is adjusted, it is constant power speed.
2. Fans and pump loads
With the rotation of the impeller, the torque decreases according to the square of the speed, and the power required for the load is directly correlated with the power of the third power of the speed. When the required air volume and flow rate are reduced, the frequency converter can be used to adjust the air volume and flow rate by speed regulation, which can greatly save electricity. Because the required power increases too quickly with the rotational speed at high speed, the fan and pump loads should not be operated at excessive power frequency.
3. Constant torque load
The TL is always constant or basically constant at any speed. When the frequency converter drags a load with constant torque properties, 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 performance of the motor to avoid burning out due to excessive temperature rise.
3. Precautions when choosing a frequency converter
Don’t just look at the price, some inverters have low prices, but the quality and performance are extremely poor. It cuts corners, has a short life, few accessories, and is difficult to maintain, and if the entire circuit board is replaced, the maintenance cost will be sky-high. Some companies can promise warranty service, but your inverter may have to be shipped to a city thousands of miles away, and it may take a month or two to repair. Although some inverters are famous brands, they are very squeamish, and they must have a good use environment to have good quality. Some inverter components are more “exclusive”, difficult to buy and expensive, so the maintenance cost is also high. Another problem with poor performance inverters is that once burned out, it is quite serious, almost no maintenance value, and the failure rate of the inverter is relatively high, so when purchasing, you should understand whether it is convenient to repair, such as whether there is a maintenance service center near you, whether the inverter module is universal, and whether it is easy to buy. If a frequency converter is used in large quantities, it is best to buy one or two more units as a backup. If your drive is used for simple speed control, choose the economical series that is cheaper.
● When the power frequency motor is dragged by a frequency converter, 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, it will produce moreHigh harmonics。 These higher harmonics will increase the output current value of the frequency converter. Therefore, when choosing a frequency converter, it should be one gear larger than that of ordinary motors.
● Compared with ordinary squirrel cage motors, winding motors are prone to overcurrent tripping problems, so you should choose a frequency converter with a slightly larger capacity than usual.
● When using a frequency converter to drive a geared motor, the range of use is limited by the lubrication method of the rotating part of the gear. When the rated speed is exceeded, there is a risk of running out of oil.
● The motor current value is used as the basis for the selection of 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 will reduce the power factor and efficiency performance of the motor.
● When the frequency converter wants to run with a long cable, the impact of the cable on performance should be considered, and a special cable should be selected if necessary. To compensate for this problem, the frequency converter should be enlarged by one or two gears.
●Special occasions such as high temperature, frequent switching, and high altitude will make the capacity of the frequency converter rain, so it is recommended that the frequency converter be selected according to the magnification level.
●Compared with power frequency power supply, the output capacity will be reduced by 10~20% when the frequency converter drives the synchronous motor.
●For loads with large torque fluctuations such as compressors and vibrators, and peak loads such as hydraulic pumps, you should fully understand the power frequency operation and choose a higher frequency converter.
