Abstract: This paper introduces the application of Fengguang brand high-voltage frequency converters in the ventilation fans of Cuizhuang Coal Mine in Weishan County, Shandong Province, and performs energy-saving calculations for the retrofit. The results show that using high-voltage frequency converters for speed regulation and energy-saving retrofitting of coal mine ventilation fans has good economic and social benefits.
Keywords: High-voltage frequency converter, coal mine main ventilation fan, energy saving
Abstract : This paper describes the application of the FengGuang high voltage inverter in Shandong's Weishan Cui Zhuang coal mine fan, and transformation of energy were calculated. The result shows that the high frequency of using coal energy-saving fan speed control device, with good economic and social benefits.
Key words : High voltage inverter Coal mine Main fan Energy-saving
1 Overview
Weishan County, located in southern Shandong Province and known as "China's Lotus Capital, Northern Water Town, and Hometown of the Railway Guerrilla," is named after Weishan Lake, where it is situated. During the War of Resistance Against Japan, revolutionary armed forces such as the "Weishu Brigade," the "Grand Canal Detachment," and the "Railway Guerrilla," based in Weishan Lake, created many heroic deeds worthy of being sung and praised. The song "Playing My Beloved Earth Pipa" resounded throughout the country.
Weishan Cuizhuang Coal Mine Co., Ltd. is a county-level state-owned enterprise. The company's mining area covers 12.6 square kilometers, with geological reserves of 136 million tons. It has total assets of over 1.6 billion yuan, more than 3,500 employees, and in 2010, its sales revenue reached 1.15 billion yuan, with profits and taxes of 500 million yuan and a profit of 350 million yuan. Its economic indicators, including economic efficiency, overall employee productivity, and safe production, rank among the top local coal mines in Shandong Province.
2. On-site introduction
Cuizhuang Coal Mine is located in Weishan County, Jining City, Shandong Province. The mine's ventilation system is equipped with two axial flow fans, one in operation and one on standby. Each fan is equipped with a 355kW/6kV high-voltage asynchronous motor. The main mine ventilation fan is used to provide fresh air to the mine and remove polluted air and harmful gases, significantly impacting the mine's safe production. The main ventilation fan operates continuously throughout the year, resulting in high power consumption. The required airflow is achieved by adjusting dampers or blade angles. Based on the requirements of reverse ventilation and later-stage mining operations, the designed power of the ventilation fan and its driven motor is far greater than the operating power required for normal mine production. The fan design has an excessively large margin, resulting in the fans operating under relatively light loads for a considerable period. This leads to a severe over-engineering of the ventilation system, resulting in significant energy waste. The on-site equipment is shown in Figure 1.
3. The Necessity of Upgrading Mine Ventilation Fans to Variable Frequency Speed Control
In coal mine production, the required air volume and pressure vary at different stages. To meet these production requirements, coal mines typically employ the following methods for adjustment:
(1) Gate regulation;
(2) Change the speed of the ventilation fan;
(3) Change the angle of the guide vane;
(4) Change the installation angle of the moving blades in the axial flow fan;
(5) Adjust the tail fin angle of the centrifugal fan;
(6) Change the number of moving blades in an axial flow fan;
(7) Axial flow fans change the angle of the stationary blades.
Among these methods, gate adjustment is the least efficient, as it artificially alters the resistance curve, increasing wind resistance, and its performance deteriorates with each adjustment. Lead vane adjustment and tail fin tilting angle adjustment are more efficient than gate adjustments. Changing the blade installation angle and the number of blades can alter the fan's characteristic curve, allowing the fan to operate at higher efficiency over a wider range, thus achieving energy conservation and consumption reduction. Changing the fan speed to operate at its optimal operating point allows the fan to operate at maximum efficiency over the largest possible range, resulting in good energy-saving effects.
If high-voltage AC variable frequency speed control technology is used, the fan speed can be adjusted by changing the frequency until the mine ventilation needs are met. If the high-voltage frequency converter fails, it can quickly switch to mains frequency operation without affecting mine ventilation. Through the high-voltage frequency converter, the fan can adjust its speed in real time according to the mine ventilation requirements, ensuring it always operates in the high-efficiency range. The application of high-voltage variable frequency speed control technology in high-power mine ventilation fans has its unique characteristics; a 10-minute shutdown of the ventilation fan constitutes a major accident, therefore, the reliability of the frequency converter and the safety design of the system are of paramount importance.
To reduce the energy consumption of the ventilation fans and improve their operating efficiency, the mine leadership, after careful consideration, decided to use the JD-BP37-400F high-voltage frequency converter manufactured by Shandong Xinfengguang Electronic Technology Development Co., Ltd. to upgrade the mine's main ventilation fans. In April 2010, the high-voltage frequency converter was put into operation in the mine's ventilation shaft, and the upgrade achieved its intended purpose.
4. Technical parameters of Fengguang brand JD-BP37-400F high-voltage frequency converter
Shandong Xinfeng Photovoltaic Co., Ltd. is a national high-tech enterprise. Its Fengguang brand JD-BP37 series high-voltage frequency converters have won the title of "China Famous Brand". The high-voltage frequency converter uses a high-speed DSP as the control core and adopts speed vector control technology and power unit series multi-level technology. It is a high-high voltage source frequency converter. Its harmonic index is far lower than the national harmonic standard of IEEE519-1992. It has a high input power factor and good output waveform quality. It does not require input harmonic filters, power factor compensation devices and output filters. It does not have problems such as additional motor heating and torque pulsation, noise, output dv/dt, common mode voltage caused by harmonics. Ordinary asynchronous motors can be used.
The technical parameters of the JD-BP37-400F high-voltage frequency converter are shown in Table 1.
5. Modify the main circuit control scheme
The wind-solar high-voltage variable frequency speed control system consists of a primary circuit incoming cabinet (bypass cabinet), a transformer cabinet, a frequency converter unit cabinet, and an operation control cabinet. During frequency converter maintenance or in the event of a frequency converter failure, the bypass cabinet connects the motor to the mains power grid, ensuring uninterrupted production. During frequency conversion operation, the frequency converter provides comprehensive protection for the motor. The primary circuit of the high-voltage frequency converter bypass cabinet is shown in Figure 2.
DL: User high-voltage circuit breaker
K1, K2, K3: High-voltage frequency converter with built-in high-voltage disconnect switch
BPQ: JD-BP37-400F High Voltage Frequency Converter
D: 355kW/6kV asynchronous motor
The manual bypass cabinet in Figure 2 contains three high-voltage disconnect switches. To ensure that power is not fed back to the inverter output, K2 and K3 use an electromagnetic interlocking operating mechanism to achieve electromagnetic interlocking. When K1 and K3 are closed and K2 is open, the motor operates at the inverter frequency; when K1 and K3 are open and K2 is closed, the motor operates at the power frequency. At this time, the inverter is isolated from the high voltage, which facilitates inspection, maintenance, and debugging.
The bypass cabinet must be interlocked with the upstream high-voltage circuit breaker DL. When DL is closed, it is absolutely forbidden to operate the bypass disconnect switch and the frequency converter output disconnect switch to prevent arcing and ensure the safety of operators and equipment. The operation of the high-voltage frequency converter on site is shown in Figure 3.
6. Effects of frequency conversion retrofitting of ventilation fan system
Ventilation fans are high-energy-consuming auxiliary equipment in coal mines. Their output power cannot change with load variations; air pressure and air volume can only be adjusted by changing the angle of the fan blades and the damper, resulting in a significant portion of energy being wasted in throttling losses. To address this energy waste, upgrading coal mine ventilation fans using high-voltage variable frequency technology is an effective way to save energy, reduce consumption, and improve the operating efficiency of ventilation fans in coal mines.
6.1 Introduction to the Variable Frequency Drive Retrofit of Ventilation Fans
Cuizhuang Mine is a newly built mine. In the later stages of production, the air resistance is relatively high. Therefore, based on data provided by the mine's ventilation department, the fans are designed for an air volume of 82.5 m³/s and an air pressure of 1764 Pa during the easy production phase, and 83 m³/s and an air pressure of 2646 Pa during the difficult production phase. Two axial flow fans are used, serving as backups for each other. The fans are 2K58-NO.24 axial flow fans with a speed of 743 r/min. They are equipped with Y450-8 motors with a rated power of 355 kW, a rated voltage of 6000 V, a rated current of 45.7 A, and a rated speed of 743 r/min. The fan characteristic curves are shown in Figure 4.
Due to the short construction period and relatively small actual ventilation requirements, the fan was initially put into operation at a 32.5° angle by adjusting the fan blade angle. Measurements taken by the mine's testing center showed the following: damper opening 2m, fan blade angle 32.5°, fan airflow 85m³/s, fan negative pressure 1750Pa, motor current 43A, and motor power 344kW. The fan operates in an inefficient range at full speed. Adjusting the fan blade angle and damper to regulate airflow and pressure, based on the mine's actual ventilation needs, results in significant energy waste.
Based on the above information, and according to the technical parameters and drawings provided by the fan manufacturer, the operating characteristics of the fan were obtained. Based on the fan characteristic curve provided by the manufacturer, the expected operating point for the fan was determined. When the fan blade angle was changed to 40° and the fan speed was simultaneously reduced to 654 r/min, the fan operated in the high-efficiency region of the characteristic curve. Measurements after variable frequency operation showed: inverter input current 24A, operating frequency 44Hz, power factor 0.975, negative pressure 1700Pa, air volume approximately 82.5 m³/s, and the actual measured fan efficiency reached 81%. This fully meets current production needs.
Meanwhile, to prevent major failures of the frequency converter, a power frequency bypass circuit was designed. In the event of a major failure, the system can put the fan into power frequency operation to ensure the continuity of production and avoid affecting coal mine production due to ventilation.
6.2 Energy-saving benefits of using variable frequency drives for ventilation fans
Based on the above, the efficiency of the fan after modification is 81%. After measuring the power factor of the variable frequency drive, the power consumption of the motor is:
P2=1.732×6×24×0.975=243.17kW.
At power frequency, the power consumed by the motor is: P1 = 344kW.
Assuming 24-hour operation per day and 300 days per year, the energy savings of the ventilation fan after adopting variable frequency technology are calculated as follows:
Annual electricity savings: (P1-P2)×24×300=(344-243.17)×24×300=725976(kW·h).
Based on a cost of 0.6 yuan per kW·h, the annual electricity savings are:
(725976×0.6)/10000=435,600 yuan.
Estimate the power consumption savings in power supply lines after adopting frequency conversion technology:
Calculate the line power factor at power frequency using the following formula:
6.3 Other benefits
(1) Variable frequency starting has no impact on the power grid. Because the fan achieves soft starting after the frequency converter is modified, the impact of starting current is avoided, and it can be started or stopped at any time.
(2) Adjust the air volume as needed to avoid waste. After the frequency conversion modification, the air volume of the fan no longer needs to be adjusted by the fan blade angle and the damper, but is achieved by adjusting the fan speed through frequency conversion. The adjustment range can be from 0% to 100%. Therefore, the air volume can be adjusted in real time according to the ventilation needs of the well, reducing unnecessary waste.
(3) Reduce the working intensity of the fan and extend the service life of the equipment. After the frequency conversion modification, the fan operates at a lower speed for most of the working time, which greatly reduces the mechanical intensity and electrical shock of the fan and greatly extends the service life of the fan.
(4) The noise of the fan equipment is reduced, which improves the working environment.
(5) Improved the level of automation control of the ventilation fan.
In the past, ventilation fans relied on manual adjustment of dampers and lacked automatic real-time airflow adjustment, resulting in low automation. After the frequency converter upgrade, the ventilation fans are controlled by frequency converters and strictly controlled according to the program. The mine monitoring room displays various electrical parameters of the ventilation system and the operating status of the equipment (working, stopped, faulty), realizing automatic control of the ventilation fans in the production process.
(6) The interface is in pure Chinese, which is simple and easy to use.
(7) It has complete protection functions. In addition to its own protection functions such as overvoltage, undervoltage, overheating, overload, short circuit, and phase loss, it also has automatic bypass function for fault units, external interlock protection system and frequency converter fault to power frequency function, which improves the safety and stability of the system.
7. Conclusion
In summary, the use of frequency conversion speed regulation for mine ventilation fans not only achieves soft start and soft stop, but also allows for convenient speed adjustment according to the ventilation needs of the roadway, resulting in a highly satisfactory retrofit effect. In 2006, Fengguang Company pioneered the frequency conversion retrofit of mine ventilation fans at Ningxia Coal Industry Company, marking the beginning of the application of domestically produced high-voltage frequency converters in mine ventilation fan retrofitting. Since then, the application of frequency conversion in coal mine ventilation fans has increased significantly. Fengguang Company's high-voltage frequency converters have achieved excellent results in the coal industry, and Fengguang products have contributed to promoting national energy conservation and emission reduction efforts.
References
[1] High Voltage Variable Frequency Speed Control System Commissioning Outline for Cuizhuang Coal Mine, Weishan County, Shandong Province Xinfengguang Electronic Technology Development Co., Ltd.
[2] User Manual for High Voltage Frequency Converters, Shandong Xinfengguang Electronic Technology Development Co., Ltd.
About the Author
Zhu Gengchen, male, senior engineer, is the electromechanical mine manager of Cuizhuang Coal Mine in Weishan County.
Jiao Yongnan is an engineer who works at Shandong Xinfengguang Electronic Technology Development Co., Ltd.
Production Base: Wenshang County Economic Development Zone, Shandong Province
Telephone: 0537-7237196
Postal code: 272500
Contact person for this article: Guo Peibin
Contact number: 0537-7237007
