I encountered a problem during the frequency conversion modification of the air compressor.：

What is a variable torque load? You can imagine a 10 meter long mandrel starting to roll paper 9 meters wide. At the beginning, the motor drove only the spindle. As the paper rolls more and more on the mandrel, that is to say, the diameter of the paper roll becomes larger and larger, the motor drives the mandrel and the paper roll at the same time, and the driving output force becomes larger and larger. This load is a variable torque load. Think again about a conveyor belt. The output force of the motor when there is nothing on the conveyor belt is different from the output force of the motor when there is something on the conveyor belt, and the output force of the motor increases as the weight of the things on the conveyor belt increases. This is also variable torque. Generally, the load change range of pumps and fans (including compressors) is very small once they are started, and they can be considered as constant torque loads. Now do you think it should be set to constant torque or variable torque?

This post was last edited by Hadman on 2010-9-25 07:50. Air compressors are constant torque loads and should be driven by a general-purpose inverter. The main purpose of using an inverter to drive the compressor is to reasonably adjust the set value of the air supply pressure according to the required air volume to achieve stable voltage and energy-saving operation. Select a constant torque inverter with the same capacity according to the rated power of the matching motor. The inverter must have built-in PID adjustment function and 4-20Ma, or 0-10V analog signal interface ； The voltage change rate at the place of use must be within the allowable input voltage range of the inverter. The automatic operation of the compressor is controlled by the frequency converter. After the equipment is modified, closed-loop control of the air supply pressure can be realized, which reduces the number of starts and stops of the compressor and reduces the labor intensity of the operators. ； It reduces power consumption and mechanical wear, extends the service life of the machinery, and improves economic benefits.

The energy-saving effect of the inverter needs to be considered comprehensively, and there are many influencing factors. For loads such as centrifugal fans and centrifugal water pumps, the torque is proportional to the square of the rotational speed, and the power is proportional to the cube of the rotational speed. As long as the valve is originally used to control the flow, and it is not working at full load, but is changed to speed-regulated operation, power saving can be achieved. For loads such as Roots blowers, the torque has nothing to do with the speed, that is, a constant torque load. If the original method of adjusting the air volume by releasing the excess air volume through the air release valve is changed to speed-adjusted operation, power saving can also be achieved. For constant power loads, such as batching belt scales, under a certain set flow rate, when the material layer is thick, the belt speed slows down. ； When the material layer is thin, the belt speed increases. The application of variable frequency speed regulator in this type of load cannot save electricity.

When using or not using a frequency converter, don’t just consider energy saving. Consider the use of frequency converters. One is for energy saving, and the other is to achieve process speed regulation. Not all situations where fans and similar loads are used can save energy, or it is not necessarily possible to use frequency converters for fans and pumps. Energy saving, for example, if the valve opening of the fan is greater than 90% without using frequency conversion, and the operating conditions are stable, then with frequency conversion, there is not much room for energy saving. Frequency conversion itself is a large investment and has efficiency issues, so in this case, there is no need to use frequency conversion. I think that as long as the speed regulation is not required by the process, you should pay attention to the economy when using frequency conversion. Treat specific problems in detail, analyze and calculate first, and then make a decision.

For frequency conversion transformation of variable torque loads such as fans and water pumps, the energy-saving effect is obvious, and the power is proportional to the cube of the speed. For frequency conversion transformation of constant torque loads, the power is proportional to the speed. And what type of load does the compressor belong to? Is it a constant torque load or is the power proportional to the 1.5th power of the speed? ? ? ? If there are two 30KW fans, one operates at industrial frequency and the other operates at 30HZ variable frequency. At this time, the energy saving is 30 * (1-0.6 * 0.6 * 0.6) = 23.52KW: If two frequency converters are used, each working at 40HZ, the power will be saved.: 2 * 30 (1-0.8 * 0.8 * 0.8)=29.28KW Is my calculation method correct? ? ? ?

I encountered a problem during the frequency conversion modification of the air compressor.: The inverter I bought is universal. When setting the parameters,: Is it time to set a "constant torque load" or a "variable torque load"? Because the energy savings of constant torque loads and variable torque loads are different. What will happen if I set it to "variable torque load"? ? ? Will there be insufficient torque? ? ?

I think we should choose based on the actual situation

First of all, the poster's energy-saving calculation formula is wrong, because when the frequency conversion is running at 30HZ, when the frequency converter is not used, the air volume is controlled by the valve, and the motor is not working at full load, so the above calculation formula is wrong. The load with constant torque uses the variable torque drag mode. I don't know if anyone has tried it. Such experience should be very little. The poster uses a Schneider inverter. The main purpose of choosing a frequency converter to drive the compressor is to reasonably adjust the set value of the air supply pressure according to the required air volume to achieve stable voltage and energy-saving operation.

How will it operate after the modification? How much energy saving efficiency can be achieved? How long will it take to recoup the renovation costs? Is there any damage to the equipment itself after the modification or any adverse effects on certain components during long-term operation?