This enterprise is a large-scale modern coal preparation production enterprise. The core production equipment in the coal preparation production system, such as jigs, scraper conveyors
1.Harmonic Hazard during installation
This enterprise is a large-scale modern coal preparation production enterprise. The core production equipment in the coal preparation production system, such as jigs, scraper conveyors, centrifugal dehydrators, and belt conveyors, all adopt 690V low-voltage power distribution and supply. Various inductive and variable frequency loads account for over 80% of the total. During equipment operation, a large amount of reactive power is generated, and variable frequency equipment causes excessive harmonic distortion in the power grid, resulting in the power factor of the 690V distribution system in the plant area being maintained at 0.70-0.73 for a long time. The utilization rate of 690V power supply equipment and transformers is less than 70%. The system also frequently encounters issues such as grid voltage fluctuations, three-phase imbalance, equipment start-stop failures, and incorrect triggering of variable frequency equipment, which seriously affect the continuous and stable operation of the coal preparation production line. Frequent equipment failures also increase maintenance costs, and there are potential electrical safety and production safety hazards caused by power quality issues. As the project leader, we implemented the reactive compensation cabinet transformation and upgrading of the 690V system in this coal preparation plant, taking overall responsibility for core aspects such as site survey, scheme customization, equipment selection, and completion acceptance, to ensure that the power quality meets the actual production needs of the coal preparation plant and achieve transformation and upgrading to meet production operation requirements:
2.Key technical difficulties and solutions of the project:
1) The 690V system in the coal preparation plant has complex load types, including a large number of variable frequency, impact, and inductive loads. The reactive power fluctuation is irregular, and different equipment is scattered across various areas of the production workshop. Traditional centralized compensation methods have low accuracy and strong lag, while local compensation can easily lead to waste of compensation capacity.
Solution: Replaced the traditional capacitor plus reactance compensation mode with a hybrid mode combining silicon carbideAPF and SVG compensation. Set up a centralized compensation cabinet in the 690V main distribution room to meet the overall reactive power demand of the system. Removed the original compensation components. Since the compensation capacity in the cabinet was the installed capacity before, it is now replaced with SVG module compensation for output capacity. The actual capacity is 20% higher than before, which can better improve the power factor and control the compensation response time within 10ms. This not only solved the problem of compensation lag but also avoids overcompensation and capacity waste.
2) The coal preparation plant production site features high dust concentration, significant equipment operation vibration, and a maximum air relative humidity of 93%. The installation area for 690V power distribution system equipment is space-constrained, and common low-voltage electrical equipment is prone to component dust accumulation and short circuits, loose wiring, and moisture-induced failures. Additionally, traditional equipment occupied a large area, which can easily conflict with coal preparation production equipment and transportation lines. (The active filter is small in size, comes with an independent air duct, and is not affected by carbon powder.) Solutions: During the equipment selection phase, supplierswere explicitly required to use modular components that are resistant to vibration and dust accumulation. The filter device housingwas made of 304 stainless steel, the sealing rubber stripwas made of oil-resistant and aging-resistant fluororubber, the wiring connectors are waterproof and dustproof aviation plugs, the protection level is upgraded to IP66, and equipment samples underwent dustproof, waterproof, and vibration resistance testing. At the same time, the equipment installation foundationwas subjected to seismic reinforcement treatment, and a dedicated equipment maintenance channelwas planned to ensure that the installation of the equipment does not affect the normal operation of the existing coal preparation production facilities.
3) The operation of a large number of variable frequency devices in the coal preparation plant generated characteristic harmonics of 3rd, 5th, and 7th order, which, combined with the impact of impact loads, led to a harmonic distortion rate of up to 12% in the 690V system and a three-phase imbalance exceeding 8%. This results in increased losses in transformers and power supply lines, shortened equipment service life, and harmonic interference that is prone to cause malfunctions in variable frequency devices and control modules, affecting production stability.
Solution: Installed a silicon carbide active power filter device in the 690V power distribution system. This product features small size, high efficiency, and is more energy-saving than traditional active filters, with the addition of an independent air duct. It precisely filtered out the main characteristic harmonics of the 3rd, 5th, and 7th order, reducing the system harmonic distortion rate to below 5%. A three-phase balance adjustment modulewas added to monitor the three-phase current and voltage changes in the grid in real time, automatically adjust the compensation capacity of each phase, and control the three-phase imbalance within 3%. At the same time, harmonic protection and overcurrent protection deviceswere installed on transformers and power supply lines. Harmonic and three-phase imbalance warning thresholdswere set in the power quality online monitoring system to achieve real-time monitoring, active management, and early warning of the power quality of the 690V system. This significantly reduced the loss of power supply equipment and extends the service life of the equipment.
3.Project implementationresults:
Through 6 months of continuous operation monitoring, all technical indicators of the Project have reached and exceeded the expectations, which completely solved the long-term power quality problems faced by 690V power distribution system of the coal preparation plant. The utilization rate of 690V power supply equipment and transformer has increased from 85% to 92%, completely solved the problems of grid voltage fluctuation, harmonic wave exceeding the standard, three-phase imbalance and equipment startup and shutdown faults, guaranteed the continuous and reliable operation of jigs, conveyors and other core production equipment, eliminated the electrical safety and production safety hazards caused by power quality problems, and the equipment failure and shutdown rate has reduced by 95%.
Feedback from the Owner: The Owner spoke highly of the implementation effect of the Company, and thought that we have completely solved the core problems of 690V power distribution system, such as poor power quality, high energy consumption and production affected for a long time. The Company has achieved remarkable results in ensuring continuous and stable operation of coal preparation production line and realizing cost reduction and efficiency increase. The Company is highly satisfied with the construction quality, progress control, technical scheme and later-stage technical service of the Project. We have subsequently reached a long-term technical cooperation agreement and entrusted us to be responsible for the subsequent high and low voltage electrical system upgrading, power quality maintenance of the Company.