Application of the hottest non inductive vector co

Application of non inductive vector converter in energy saving transformation of air compressor

1 Air 2. Zhangyuhui, senior engineer of China Academy of building materials science, made a report on the general situation of the compressor in the classification of the combustion performance of building materials and products (GB8624 ⑵ 012):

1.1 working principle of the air compressor

we know that the compressor has been successfully trial produced in Germany in 1640 and has a history of hundreds of years. Compressor is a kind of machine that compresses gas so as to improve gas pressure or transport gas. For example, piston air compressor is a kind of machine that the motor drives the pulley to directly drive the crankshaft through the coupling, drives the connecting rod and piston rod, so that the piston makes reciprocating motion in the compressor cylinder, completes the processes of suction, compression, discharge, etc., boosts the pressure of non pressure or low-pressure gas, and outputs it to the pressure storage tank. Among them, the piston assembly, the piston, the inner wall of the cylinder and the cylinder head form a working chamber with variable volume. Driven by the crank and connecting rod, it makes reciprocating motion in the cylinder to realize the compression of the gas in the cylinder

air compressors are widely used in many departments of national economy and national defense construction, especially in petroleum, chemical industry, power and other industrial fields. They have become essential key equipment and core equipment in the process flow of many industrial departments. Providing sufficient supply pressure of compressed air required for automatic production is an essential factor for smooth production process. Instantaneous pressure drop will affect product quality

1.2 problems existing in the original system

since the air compressor cannot rule out the possibility of long-term operation under full load, the capacity of the motor can only be determined according to the maximum demand, and the design margin is generally too large. The impact of power frequency starting equipment is large, and the wear of motor bearings is large, so the equipment maintenance is large. Although they are all started by reducing the voltage, the current at the time of starting is still very large, which will affect the stability of electricity and the operation safety of other electrical equipment, and most of them are continuous operation. Because the driving motor of general air compressor itself cannot adjust the speed, it is not possible to directly use the change of pressure or flow to realize the matching of speed reduction adjustment output power, and the motor is not allowed to be started frequently, As a result, when the air consumption is low, the motor still has to run without load, resulting in a huge waste of electric energy

frequent unloading and loading lead to frequent changes in the whole gas pressure, which cannot maintain a constant working pressure and prolong the service life of the compressor. Some adjustment methods of the air compressor (such as adjusting the valve or adjusting the unloading, etc.) even when the flow is small, because the motor speed remains unchanged, the reduction of motor power is relatively small

to sum up, if frequency conversion speed regulation technology can be adopted, when the flow demand is reduced, the speed of the motor can be reduced, so as to greatly reduce the operating power of the motor, and the purpose of energy saving can be achieved

2. The design requirements of frequency conversion transformation scheme

according to the problems existing in the original working condition and in combination with the production process requirements, the system after the frequency conversion transformation of the air compressor should meet the following requirements:

1) the frequency conversion operation state of the main motor should keep the outlet pressure of the air tank stable, and the pressure fluctuation range should not exceed ± 0.02MPa

2) the system shall have two sets of control circuits of frequency conversion and power frequency to ensure that the production will not be affected in case of abnormal tripping protection of frequency conversion

3) under the condition of small electrical quantity, when the frequency converter is running at low frequency, the motor winding temperature and motor noise shall not exceed the allowable range

3. Precautions for frequency conversion transformation of air compressor

1) the air compressor is a load with large moment of inertia, and this starting feature is easy to cause the frequency converter with v/f control mode to skip current protection during starting. It is recommended to select the speed sensorless vector frequency converter with high starting torque, which has issued a non public additional plan, so as to ensure the continuity of constant pressure gas supply and the reliable and stable operation of the equipment

2) the air compressor is not allowed to operate at low frequency for a long time. When the speed of the air compressor is too low, on the one hand, the working stability of the air compressor will become worse, on the other hand, the lubrication of the cylinder block will become worse, which will accelerate wear. Therefore, the lower limit frequency of operation should not be lower than 20Hz

3) in order to effectively filter the high-order harmonic component in the output current of the frequency converter and reduce the electromagnetic interference caused by high-order harmonic, it is recommended to select the output AC reactor, which can also reduce the running noise and temperature rise of the motor and improve the stability of the motor

4. Frequency conversion and speed regulation transformation scheme

there are five 132kw air compressors and one 65kW air compressor in a tire factory in Xiamen. The air pressure regulation range is large, the pressure is unstable, and there is no peak air consumption. One air compressor is idling, which consumes a lot of energy. Because the production of the company is mainly concentrated in the daytime, and the gas consumption is small at night, there is a serious phenomenon of "big horse pulling small car" at night, and the no-load time is long, resulting in a huge waste of energy. In March, 2005, after repeated technical discussion, the equipment department of the company decided to carry out frequency conversion and energy-saving transformation of the air compressor station of the plant

4.1 system parameters

1) air compressor model: L-type two-stage double cylinder compound action water-cooled air compressor 4l-20/8

2) main motor model: y315m

rated power 132kw, rated voltage 380V, Rated current 250a960r/min

3) frequency converter: komlung non inductive vector frequency converter kv2000-gt rated current 253a

4) remote pressure gauge: vtp10-a-g10-b

4.2 system working principle

according to the requirements of the uniform loading plant in the last fiscal year, we use two selection switches and two AC contactors to control the frequency conversion of any one of the two air compressors, At the same time, keep the original y- △ step-down starting cabinet, and switch to power frequency operation in case of frequency conversion failure

the variable frequency speed regulation system takes the output pressure as the control object. The system adopts Comron speed sensorless vector frequency converter and remote pressure transmitter SP to form a closed-loop constant pressure control system. The required pressure value can be directly operated by the frequency converter panel. The on-site pressure is detected by the transmitter and fed back to the frequency converter. The frequency converter compares and calculates through the built-in PID, so as to adjust its output frequency and meet the requirements of constant pressure air supply of the air compressor. (end)