Matters needing attention in frequency conversion transformation of screw air machine

1. When carrying out frequency conversion transformation, attention should be paid to keep the integrity of the main circuit and control circuit of the original equipment as much as possible, and the less changes to the circuit, the better; It can be easily changed back to the original control mode, which ensures that the air compressor can operate under variable frequency and power frequency, and also makes it unnecessary to reprogram the PLC program during the transformation.

2. The starting signal of the frequency converter is controlled by the delta connection AC contactor KM1, that is, the frequency converter does not start and has no output in star connection.

3. The setting time of the time relay JS should be greater than or equal to the starting time of the frequency converter, which ensures that the frequency converter starts with no load and variable frequency.

4. Use the lower limit frequency delay stop function of the inverter.

5. The lower limit operating frequency of the inverter should generally be set at 35 Hz or above. If the Hz is too low, the oil-gas separator may not be able to effectively separate oil and gas, resulting in oil leakage from the air compressor. However, it is necessary to consider setting the lower limit frequency value according to the actual situation, because different air compressors have different mechanical wear and efficiency, and the lower limit frequency without oil leakage is not necessarily the same.

6. It is recommended to choose a frequency converter with a power level higher than that of the air compressor to avoid frequent tripping when the air compressor starts.

7. In order to effectively filter out the high-order harmonic components in the output current of the inverter and reduce the electromagnetic interference caused by high-order harmonics, it is recommended to use an output AC reactor, which can also reduce the noise of the motor running.

8. The installation position of the pressure sensor on the pipeline should be as close as possible to the air compressor. Do not install it behind the filter or valve. At the same time, remember that no valve components can be installed on the pipeline between the pressure sensor and the air compressor to prevent the filter from clogging. Or after the valve is closed, the air compressor does not stop and there is a risk of explosion. The original pressure shutdown protection switch of the air compressor should also be retained.

9. According to the requirements of the production process, after the frequency conversion transformation, the gas supply pressure of the compressed gas supply system should be appropriately reduced, and the original high-pressure variable flow gas supply should be changed to the variable frequency constant pressure variable flow gas supply mode.

10. The designed system should have two sets of control loops of frequency conversion and power frequency to ensure that the production will not be affected when the frequency conversion is abnormally tripped and protected.

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