Application and Analysis of FGI Explosion-proof SVG in the Underground Power Supply System of Coal Mines
In July 2007, the National Development and Reform Commission and the State Environmental Protection Administration clearly stated in the "Notice on Opinions for Energy Conservation and Emission Reduction in the Coal Mine Industry" that dynamic reactive power compensation and local reactive power compensation strategies should be adopted in underground coal mines to ensure that the average power factor of the power supply lines after compensation is greater than 0.9. However, the total installed capacity of the working faces in the underground power supply systems of the existing operating coal mines and under-construction mines in our country will increase significantly with the improvement of production in the mining area or the renewal of equipment. In addition, during the design stage of mine exploitation, the power supply lines are too long, and the concentrated use of a large number of high-load mining and transportation equipment leads to the proportion of reactive power in the power consumption system. At present, the average power factor of the power supply system in most underground working faces that are not compensated by equipment usually does not exceed 0.7. However, in the state where motor equipment is frequently started, the power factor may even drop below 0.4.
The excessive content of reactive power in the underground power supply system not only seriously affects the power quality in underground coal mines, but also brings challenges to the design of power supply lines for underground coal mining and tunneling working faces. This paper analyzes in detail the application schemes and effects of explosion-proof SVG under different working conditions in underground coal mines, explores how this technology solves the long-standing reactive power problem in coal mine production, and discusses the importance and practical value of configuring explosion-proof SVG devices in improving the performance of the underground power supply system in coal mines.
2.Analysis of the Current Situation of the Power Supply System in Underground Coal Mines
(1) Underground power quality issues
With the continuous advancement of mining technology in our country, the use of high-power heavy-duty mining equipment underground has become the norm. This change has effectively reduced the difficulty of large-scale coal resource mining. With the gradual extension of the distance between coal mining and tunneling equipment and power supply equipment, as well as the increase in the proportion of variable frequency equipment usage, the economic benefits of coal mining production enterprises have significantly improved. However, these developments are also accompanied by various problems of power quality in the underground power supply system, specifically manifested as low power factor, voltage drop at the end of the line, sudden voltage drop, poor power supply stability, voltage fluctuation and voltage flicker, etc.
With the wide application of various electronic devices such as frequency converters, winches, pneumatic drills and electric locomotives in coal mines, these devices often have the characteristics of nonlinear impact and imbalance. During their operation, they will generate a large amount of high-order harmonics, thereby causing distortion of the current and voltage waveforms at the input end of the equipment, and further affecting the difficulty of starting the equipment. In addition, the existence of high-order harmonics not only makes it difficult to start large equipment, increases the wear and tear of the equipment during the start-up process, but may also cause frequent burnout or tripping of the equipment. These problems not only increase the operating costs of electrical equipment, causing it to overheat, reduce efficiency and lower safety, but also threaten the reliability of the upper-level relay protection equipment, possibly triggering various protection systems to malfunction or fail to operate. In addition, harmonics to a certain extent may cause local resonance in the system, thereby interfering with the normal operation of electrical equipment. This kind of interference not only reduces the insulation performance of mining equipment, increases the risk of electrical safety accidents, but also seriously affects the safe operation and production efficiency of coal mines.
(2) The influence of reactive power on the design of underground long-distance power supply systems
The design of the power system in coal mines is restricted by factors such as the geological characteristics of the mining area and the economic benefits of coal mining. Therefore, the layout of the power supply system is relatively complex. Under normal circumstances, the topological structure of the coal mine power supply system is shown in Figure 2. The 35(10)kV substation on the surface supplies power to the substation in the mining area through the central substation, and then the substation in the mining area converts the voltage to 3.3kV/1.14kV through the mobile substation to supply the temporary distribution points in the mining and excavation work faces. In this power supply system, the longest 10(6)kV cable from underground to the end mining area substation is up to 10 kilometers in length and contains multiple branches. The farthest distribution point at the end working face can be up to 5 kilometers away from the mining area substation, and the voltage drop at its end exceeds 7% of the rated voltage. Also according to the requirements of the demand for different working conditions mining technological requirements of power supply will be mobile transformer substation configuration in the mining area or face entrance, 3.3 kV power supply from 1 to 5 kM (1.2). Considering that high-power equipment generates a large amount of reactive power in the underground power supply system during startup and normal operation, the resulting impulse reactive current causes a voltage drop exceeding the rated voltage by 25% at the end of long-distance lines, resulting in the inability of the equipment at the working face to operate normally.
3.FGI's solution to the underground power supply problem
(1) Centralized compensation solution
The 10kV/6kV large-capacity reactive power compensation device is suitable for installation in underground high-voltage distribution points. It can centrally compensate for all loads of multiple power consumption working faces supplying power to this distribution point, effectively improving the power quality and power factor of the power consumption working faces from the perspective of the entire power supply system, while filtering out harmonics in the power grid. Thereby enhancing the transmission capacity and power supply efficiency of the power supply lines. Furthermore, this compensation scheme can significantly enhance the stability and energy-saving effect of long-distance power supply by stabilizing the voltage. This technical configuration not only optimizes the operational efficiency of the power system, but also helps to reduce operation and maintenance costs and achieve efficient and stable power supply.
The centralized compensation solution can effectively compensate for the reactive current in the high-voltage power supply lines and significantly reduce the system loss by lowering the reactive current loss of the lines. Meanwhile, the power factor of the system can be improved. By precisely selecting reactive power compensation equipment based on the electrical equipment, the power factor can be increased from below 0.5 to 0.99. In addition, this technology can also filter out the harmonics existing in the system, reduce the faults of electrical equipment caused by harmonics, and enhance the operational stability of electrical equipment. By enhancing the reliability of equipment, the costs of human and material resources can be significantly reduced, and the maintenance and operation efficiency of the equipment can be optimized. The application of this technology not only improves the power quality, but also helps to extend the service life of equipment and enhance the economy and environmental friendliness of the entire power supply system.
(2) Decentralized and local compensation solutions
The 3.3kV/1.14kV explosion-proof SVG is configured in the 3.3kV/1.14kV power supply line of the working face. It can perform directional compensation for one or several loads in a certain production working face, effectively improving the power supply branch factor, reducing cable power loss, enhancing the utilization rate of the upper-level mobile transformer, and lowering the transformer voltage drop. To achieve the purpose of extending the power supply to the mining and excavation working face.
4.Sum up
In conclusion, in the power supply system of coal mines, the deployment of SVG is of great significance for optimizing the underground power supply system. This move can not only improve the power quality of the power supply system, but also help reduce the line current by compensating reactive power, thereby extending the power supply distance of the working face. The application of this technology can solve various problems faced by the existing underground power supply system, achieve energy conservation and consumption reduction, and provide support for China to achieve the goals of carbon peaking and carbon neutrality.
