Application of Air Compressor
of ACI V11 Inverter in Energy Saving Transformation
1、Working Principle of Air Compressor
Air compressor is the main body of the air source device. It is the air pressure generating device for compressed air that converts the mechanical energy of a prime mover (usually an electric motor) into a gas pressure energy. It has a very wide range of applications in industrial production and is responsible for all pneumatic components for the plant and a variety of pneumatic valves to provide gas sources of responsibility in a variety of industries. Therefore, the operation of air compressor directly affects the production process of the factory. There are many types of air compressor (mainly divided into screw type and piston type, and screw type has the most widely application), the control mode of air supply of air compressor is controlled by loading and unloading the pressure of gas storage tank in the range.
1)Working principle of piston type air compressor
The motor of piston type air compressor drives the crankshaft by driving the belt pulley to drive the shaft, and it drive connecting rod and piston rod for the reciprocating motion of the piston in the cylinder of a compressor. It completes the process of suction, compression and discharge, and steps up the pressure of no pressure or low pressure gas, and output to the storage tank. The piston ring, the piston and the inner wall of the cylinder and the cylinder cover form a volume variable working cavity, which has the reciprocating motion to achieve the cylinder gas compression in the cylinder by the driving of crank connecting rod.
2) Working principle of screw air compressor
Screw type air compressor achieves the air periodic volume change between rotor slot by a pair of parallel meshing rotors (or screw rotation). The air is conveyed from the suction side to the output side along the rotor axis, and the whole process of the air suction, compression and exhaust of the screw air compressor is realized. The air inlet and outlet ports of the air compressor are located at both sides of the shell, the cathode and the anode of the rotor slot of the rotor tooth is driven by the main electric motor rotation.
2、Necessity of Energy Saving Transformation of Air Compressor
Because the air compressor maybe run in full load condition for a long time, type selection can only be determined by the maximum demand to determine the motor capacity.It cause that air compressor system is generally too large. The traditional air compressor uses star delta ,autotransformer or frequency sensitive rheostat to start.So it will affect the stability of the power grid with large impact and starting current of 2~3 times rated current. And the most of air compressors are running continuously, and because the air compressor motor itself cannot achieve the reduction of speed according to the pressure changes in demand to matching the output power of the motor with the actual pressure demand of the field, which results in operating with no load when the amount of gas is low . It causes the huge waste of energy. According to statistics, the power consumption of air compressor accounted for 15% of the power consumption of industrial equipment. Therefore, air compressor is necessary for energy saving transformation, in addition, the air compressor also has the following problems:
1) The air compressor is unloaded when the pressure exceeds the upper limit, but the motor is still in idling at this time. It wastes a large amount of electric energy and increases the wear of the motor bearing.
2) Frequent loading and unloading caused the impact on the power grid, which will make power grid voltage more fluctuations and increase the mechanical wear, shorten the mechanical life.
3) Volume cannot keep constant pressure. When the gas consumption is changing, the pressure of the gas supply will inevitably fluctuate, the accuracy of the gas can not reach the requirements of the process, which affects the production efficiency and product quality.
In summary：If the air compressor uses the frequency speed regulation technology which reduces the gas consumption and increases the pressure of the gas storage tank ,it will achieve the purpose of energy saving
by regulating the frequency converter PID, reducing the motor speed and the motor running power.
3、Features of DLT Series Air cCompressor Frequency Conversion and Constant Pressure Control System
①DLT series of air compressor energy-saving cabinet frequency control system will control pressure pipe network as the object. The pressure value is given by the inverter panel (there are several given channels),which can freely be set in air compressor maximum allowable working pressure according to the actual needs of gas equipment. The pressure transmitter which is connected with the gas storage tank changes the pressure of the gas storage tank into a 4~20mA current signal to the power saving cabinet built-in PID regulator, which compared with the pressure of a given value, and according to the difference of the size of the inverter output frequency control, adjust the speed of the motor, so that the actual pressure is always maintained at a given pressure. DLT series air compressor power saving cabinet built-in PID has high stability, simple debugging features.
1）Operating cost reduction: The running cost of air compressor is composed of three parts: initial purchase cost, maintenance cost and energy cost. The energy cost accounts for about 70% of the operating cost of the compressor. By reducing energy costs 30%, and coupled with the frequency of the impact of the device after the start of the reduction, maintenance and maintenance of the amount will be reduced, the running costs will be greatly reduced.
2）Improve the quality of gas supply: The variable frequency control system has the ability of accurate pressure control. By matching the air pressure of the air compressor with the gas demand, the system pressure of the pipe network can be kept constant, which can effectively improve the quality of the air supply.
②3）power saving cabinet has soft start function, which can reduce the impact of the mechanical parts of the compressor when starting, enhance the system reliability, prolong the service life of the compressor and reduce the impact of air compressor starting on the power grid at the same time.
4、Notes on The Design of Frequency Conversion System
1）Air compressor does not allow for long periods of low frequency operation. If the air compressor speed is too low, on the one hand, it will make the air compressor work stability becomes poor ,and noise increases. On the other hand, the cylinder lubrication conditions become worse, wear increases, and then result to the injection phenomenon. So, the lower frequency of air compressor work should not be less than 25Hz (Motor cooling conditions are poor with high temperature rise below 25Hz.It is also easy to reduce the motor insulation and service life) , and deceleration time should be as short as possible. G11 whose voltage fluctuation range is + 15%, and the pressure is high can set a short deceleration time, so as to avoid the slow down time is too long to produce the fuel injection phenomenon.
2）In the production process to meet the requirements, the lower the pressure set is better. When the air compressor works, the more the motor shaft power consumption is caused by the higher pressure and the compression ratio.
3）The air supply pipe network should be no leakage phenomenon, in order to avoid the resulting energy waste.
Application example 1:Fuoshan Zhongbang textile company uses the Sullair air compressor with 280kW motor and 280kW V11 vector type inverter. Set the acceleration time for 12S, deceleration time for the 5S, set the pressure 0.72MPa. Pressure stability in 0.71~0.73MPa. Operation data is as follows:
Application example 2:Guangzhou Huadu Tongchang Paper Co., Ltd. has four units of 30kW air compressors with air compressor dedicated controller ACI KYK3/KB of Guangzhou Zhufeng Electric Co.,Ltd . The controller is controlled by microcomputer, which can realize intelligent operation, including automatic control of air compressor exhaust temperature, various failure detection and real time display of air compressor, fault protection and shutdown. The special controller of air compressor is composed of the control module and the display screen. The controller with high performance G11 inverter composed of DLT series air compressor special power saving cabinet can effectively control the stable operation of air compressor, which has small noise even in 25Hz. It can not only save energy, but also reduce the mechanical wear of air compressor, improve the service life of the bearing, reduce maintenance costs, reduce operating costs with comprehensive benefits.
After the transformation, the operating current and motor power consumption will reduce (18% power), and maintenance cycle is extended (the original about half a year to repair once, from March 2011 to 2012 October has been stable operation), and the overall cost will reduce.
Zhufeng ACI air compressor power system is the current advance of the Zhufeng electric project which has established air compressor business department. Frequency conversion technology has been successfully applied in industrial production, and servo air compressor as the future focus of the project, also has been on the agenda of the application of electrical projects in Zhufeng.