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Application of Frequency Converter Energy Saving Technology in Coal Industry

Jan 13, 2021

Application of Frequency Converter Energy Saving Technology in Coal Industry

Coal enterprises are large power consumers. For coal mining enterprises, electricity consumption accounts for a large proportion. According to the survey, the electricity consumption of fans, water pumps, compressors, hoisting winches, and gas drainage equipment account for the entire coal mine production electricity consumption. More than 40%. The development of frequency conversion technology can effectively solve the problems of single control technology, poor real-time performance, and low degree of automation.


Application of Frequency Converter Energy Saving Technology in Coal Industry


    1. The principle and energy saving effect of frequency conversion speed regulation technology


    1. The principle of frequency conversion speed regulation technology


    AC frequency conversion speed regulation is a new technology developed in recent decades. With its excellent speed regulation performance, significant power saving effect and wide applicability in various fields of the national economy, it is recognized as the most promising Speed mode. AC variable frequency speed regulation technology is a comprehensive application of microcomputer technology, power electronics technology and motor drive technology. The basic principle is that under the on-off action of power semiconductor devices, the power frequency AC voltage is converted to DC voltage through a rectifier bridge, and then the inverter The converter converts the frequency and voltage adjustable AC voltage as the driving power source of the AC motor, so that the motor can obtain the voltage and current required for stepless speed regulation. It is one of the efficient speed regulation methods without additional slip loss.


    On the basis of the integration of strong and weak electricity and electromechanical integration, the comprehensive application of power electronic technology, micro technology and motor drive technology is called AC frequency conversion speed regulation technology. This can be used as an efficient speed regulation method without additional slip loss, and at the same time, the motor can obtain the voltage and current required for stepless speed regulation. The frequency conversion speed regulation technology developed in the energy crisis can effectively greatly improve work efficiency because it can automatically and smoothly increase and decelerate according to the motor load. In this way, through the change of the power supply frequency of the motor, the frequency conversion speed regulation technology as a high-efficiency and high-performance speed regulation means can realize effective regulation.


    2. Energy saving effect of frequency conversion speed regulation technology


    With the rapid development of electronic technology, computer technology, automatic control technology, and high-power output technology, AC motor frequency conversion speed regulation technology has made breakthrough progress and has become a major means of saving electricity, improving the environment, and promoting technological progress. Has become an inevitable development trend. Obvious energy-saving effect and superior adjustment performance make the frequency conversion energy-saving technology more and more widely used in coal mines in our country, and the technology is becoming more and more mature. Large-capacity, multi-function, and high-reliability inverters have been widely promoted and applied in coal mine production, saving a lot of electricity for coal mines, especially in fluid loads, with an energy-saving rate of 20% to 60%. The principle of frequency conversion control is: the use of frequency conversion speed regulation motor to achieve real soft start and smooth speed regulation, and the use of frequency converter control to increase the power factor of the input power supply. Below the base frequency, it is a constant torque output, and the output power changes with the speed.


    2. The specific application of frequency conversion speed regulation technology in coal mine production takes belt conveyor as an example


    1. Energy-saving problem of belt conveyor in coal mine production


    Belt conveyors are widely used as the main equipment for coal mine transportation. With the development of high-yield and high-efficiency coal mines, more and more long-distance, large-capacity, high-speed belt conveyors are being designed, manufactured and put into operation. The use of these large-scale models has sharply exposed the problems of the conveyor's large impact load and uneven output of the drive motor, resulting in motor overload. The start-up and operation mode of the belt conveyor is that the winding motor runs at power frequency after the rotor winding is stepped down and then switched to the belt conveyor through the hydraulic coupler. The working principle of the belt conveyor is that the belt conveyor drives the belt by friction through the drive hub, and the belt drives the animal body to move on the supporting rollers through tension deformation and friction. The belt is an elastic energy storage material, and a large amount of potential energy is stored when the belt conveyor is stopped and running. This determines that the soft start method should be adopted when the belt conveyor starts.


    Therefore, the following requirements are put forward for the starting and operation of the belt conveyor: If the motor is directly started under heavy load, the power supply is required to provide a current 6-7 times larger than that during normal operation, so that the motor will be caused by excessive current and long starting time. Overheating burns; the power grid will affect the operation of other equipment due to the excessive reduction of the voltage due to the large current; therefore, a new drive system is required to reduce the current when the motor starts. At present, large-scale belt conveyors require the drive system to provide an adjustable, smooth, and impact-free starting torque to reduce the impact, thereby improving the force on the whole machine, extending the life of the whole machine, and improving the reliability of the equipment , That is, hope to achieve soft start. For long-distance belt conveyors, if the starting is too fast, the tensioning device will not have time to tighten, causing the transmission roller to slip, causing heat and fire; for a large-incline upward belt conveyor, if the starting acceleration is too fast, the material will fall Or rolling material phenomenon; this requires controllable starting acceleration to achieve smooth starting. In order to facilitate the maintenance of the belt conveyor, it is hoped to realize the low-speed inspection belt operation.


    In summary, the drive system is required to be able to adapt to the requirements of starting, running, and stopping conditions, so that the belt conveyor can start and stop smoothly, run efficiently, drive balanced, and work safely and reliably. However, most domestic coal mines currently use hydraulic couplings to realize the soft start of the belt conveyor, and adjust the mechanical efficiency of the hydraulic coupling to zero when starting, so that the motor starts without load. Although the rotor series resistance is used to improve the starting torque and the reduced voltage no-load start, the starting current of the motor is still large, which will not only cause severe fluctuations in the grid voltage, but also cause mechanical shock and heat generation inside the motor. At the same time, due to the long-term work of the fluid coupling, it will cause the internal oil temperature to rise, metal parts wear, leakage and efficiency fluctuations, etc., which will not only increase the difficulty and cost of maintenance, pollute the environment, but also make multiple machines drive the same It is difficult to solve power average and synchronization problems when belting.


    2. Application of frequency conversion speed regulation technology in belt conveyor


    The frequency conversion speed regulation automatic control system in the belt conveyor is composed of a programmable controller PLC, a frequency converter, a current transformer, a current transmitter, a nuclear belt scale, a belt speed sensor and a motor speed sensor, etc., which can be summarized as There are three parts: detection unit, control unit and execution unit.


    Detection unit: current transformer and transmitter obtain motor current signal. The belt speed signal collected by the belt speed sensor is converted into a voltage signal. The speed signal collected by the motor speed sensor is converted into a voltage signal. The nuclear belt scale collects the traffic signal. Each signal is sent to the core module.


    Control unit: When the PLC receives the detection signal, it completes the starting, power balance, and energy-saving speed regulation functions of the belt conveyor after judgment and decision-making. At the same time, the main control unit also has fault protection functions such as broken belt, coal pile, tearing belt, smoke, slip, temperature and so on.


    Execution unit: The frequency converter receives the frequency control signal of the PLC, and outputs the voltage of the corresponding frequency according to the given signal to the motor to realize the speed regulation of the motor and complete the various functions of the belt conveyor. After frequency conversion technology transformation, the belt conveyor has completely realized the soft start and soft stop operation mode of the belt conveyor, which makes the performance of the belt conveyor more stable in work.


    The power factor of the system reaches more than 0.9 in the whole process, which greatly saves reactive power. After using the frequency converter to drive, the total transmission efficiency of the system is 5% to 10% higher than that of the hydraulic coupling drive. After the transformation, the system can automatically adjust the output frequency and output torque according to the load changes, which changes the previous mode of motor power frequency and constant speed operation, which greatly saves power and energy consumption. Moreover, the use of the four-quadrant medium and high voltage frequency converter realizes the energy feedback function of the belt conveyor, which further reduces the energy consumption of the belt conveyor, and the withdrawal of the hydraulic coupling greatly saves the maintenance and repair costs of the equipment. It is more perfect in terms of energy saving and environmental protection.


    3. Conclusion


    In short, the application of frequency converter in coal mines has achieved good results. With the development of new power electronic devices and the continuous improvement of performance, the application of frequency conversion speed regulation technology in coal mine production will play a greater role and achieve more significant economic benefits. benefit.