1.Overview

A large metal products factory has four single-stage compression screw air compressors (hereinafter referred to as air compressors). Due to the product transformation and reduced gas consumption, after on-site observation and testing, it is believed that there is a relatively large energy saving space, so the energy saving transformation is carried out. The working principle of the air compressor is by a pair of parallel engagement of Yin and Yang rotor (or screw) rotation in the cylinder, the air between the rotor groove constantly produce periodic volume change, the air along the rotor axis from the suction side to the output side, realize the whole process of suction, compression and exhaust of the screw air compressor. The air inlet and outlet of the air compressor are located at both ends of the shell, and the groove of the Yin rotor and the Yang rotor are driven by the main motor and rotate.

2.Implementation plans

The main motor power of the original air compressor is two 75kW and two 90kW. After star-triangle decompression, full pressure operation, which is a typical no-load start and runs at full speed.

According to the above principles, the manufacturer after multiple investigation, comparison, finally choose FD300 series low voltage frequency inverter, so that the system can meet the above working conditions.

Considering the future upgrade of the whole factory automation, the inverter is required to have built-in PROFIBUS-DP bus and CANOPEN bus.

The pressure closed-loop control system consists of frequency converter, pressure transmitter, regulator, motor and spiral rotor to automatically adjust the motor speed, so that the air pressure in the gas storage tank is stable within the set range, and the constant pressure control is conducted. The feedback pressure is compared with the set pressure, and the output frequency of the frequency converter is controlled in real time, so as to adjust the motor speed, so that the air pressure in the gas storage tank is stable on the set pressure.

3.Application advantage

Save energy

The FD300 series low voltage frequency inverter control compressor and the traditional control compressor comparison, energy saving is the most practical significance, according to the air demand to supply the compressor condition is the most economical operation.

The operation cost reduction can be confirmed from the above table that the power saving effect is very obvious. If the air compressor is calculated by 300 working days per year, it can save 195,800 kilowatt hours of electricity per year.

The operating cost of a traditional compressor consists of three items: initial purchase cost, maintenance cost and energy cost. Energy costs account for about 77% of the compressor operating costs. Reduce the energy cost by 41.9%, reduce the impact on the equipment after the frequency conversion starts, and reduce the maintenance and maintenance volume, so the operation cost will be greatly reduced.

Improve the accuracy of pressure control

The variable frequency control system has a precise pressure control capability. Match the air pressure output of the compressor with the air volume required by the user air system. The output volume of frequency conversion control compressor changes with the change of motor speed. Due to the improvement of the accuracy of the frequency conversion control motor speed, it can keep the system pressure change of the pipe network within the 3 pisg change range, that is, 0.2bar range, effectively improving the quality of the working condition.

Extend the service life of the compressor

The frequency converter starts the compressor from 0Hz, and its starting acceleration time can be adjusted, so as to reduce the impact on the electrical and mechanical parts of the compressor, enhance the reliability of the system, and prolong the service life of the compressor. In addition, the frequency conversion control can reduce the current fluctuation when the unit is started, which will affect the power consumption of the power grid and other equipment. The frequency converter can effectively reduce the peak of the starting current to the minimum.

Reduce the noise of the air compressor

According to the working conditions of the compressor, the running speed of the motor after the frequency conversion speed regulation transformation is significantly reduced, so the noise of the air compressor is effectively reduced. Field measurement showed that the noise decreased by about 5 dB compared with the original system.