Application of high power voltage stabilizer on coal mine conveyor - voltage stabilizer for air conditioner

With the advancement of power electronic technology, automatic control technology and computer technology, frequency conversion speed regulation technology has developed rapidly. There are not many application examples. Mining belt conveyors are generally driven by power frequency and driven by hydraulic couplers, which have problems such as low transmission efficiency, large starting electric shock and mechanical shock, and inability to balance power, resulting in uneconomical system operation; belt and hydraulic coupling Serious wear and tear of the device, high maintenance and maintenance costs; there is reactive power circulation loss. Therefore, the use of frequency conversion control for belt conveyors is not only conducive to reducing the production cost of enterprises and improving the economic benefits of enterprises, but also in line with the theme of building a conservation-oriented society, which has very practical economic and social significance.

1 Working principle and starting method of belt conveyor

The belt conveyor drives the belt by friction through the driving drum, and the belt drives the object to move on the support roller through tension deformation and friction. The belt is an elastic energy storage material, which stores a large amount of potential energy when the belt conveyor stops and runs, which determines that the equipment should be started with a soft start method.

The traditional starting method of belt conveyor drive system adopts auto-coupling step-down, and a hydraulic coupler is installed between the motor and the reduction box. Although the hydraulic coupling can partially solve the soft start problem of the belt conveyor, it still has some shortcomings compared with the frequency converter drive:

   1) When using a hydraulic coupling, adjust the mechanical efficiency of the hydraulic coupling to zero when starting, so that the motor can be started with no load. The motor must first be started with no load. When the power frequency is started, the initial current is very large, which is 4--7 times the rated current of the motor. The large starting instantaneous current will produce impact during the starting process, causing changes in the mechanical stress and thermal stress in the motor, causing serious wear and even damage to the mechanical parts. At the same time, it will also cause the voltage of the grid to drop, which will affect the normal operation of other equipment in the grid. Therefore, the large-capacity belt conveyor must also be equipped with a motor soft-start device.

   2) When the hydraulic coupler works for a long time, the temperature of the liquid will rise, the alloy plug will be melted, liquid leakage will be caused, the maintenance workload will be increased, and the environment will be polluted.

   3) When the hydraulic coupling is used, the loading time of the conveyor is short, which is easy to cause changes in the belt tension, so the belt strength is required to be higher.

   4) Generally, belt conveyors are long-distance and large-capacity, multi-motor driven, and driven by hydraulic couplers, so it is difficult to solve the power balance and synchronization problems when multi-motor driving.

2 The advantages of frequency conversion technology transformation

The rapid development of frequency conversion technology has been well applied in coal mining enterprises. The use of frequency converters to transform the drive of belt conveyors brings great social and economic benefits to users:

   1) The soft start of the belt conveyor system is truly realized. Using the soft start function of the frequency converter, the soft start of the motor and the soft start of the conveyor are combined into one. The slow start of the motor drives the conveyor to start slowly, and the energy stored in the belt is slowly released to make it start The tension wave formed in the process is extremely small and causes almost no damage to the belt.

2) Realize the power balance when the conveyor is driven by multiple motors. When using the inverter to drive the belt conveyor, one-to-one control is generally adopted; when multiple motors are driven, the master-slave control is adopted to achieve power balance. The main shaft belt of a coal mine in Yangquan, Shanxi Province is driven by a 135kW*3 motor. After using the master-slave control, the current difference between the master and the slave motor is about 5A at light load, and the difference is about 2A at full load. It basically realizes the power balance when the conveyor is driven by multiple motors.

3) Reduce the belt strength. After using the frequency converter to drive, because the start-up time of the frequency converter is adjustable within 1S-3600S, usually the start-up time of the belt conveyor is within 60S-200S. According to the on-site setting, the start-up time of the equipment is prolonged, which greatly reduces the requirement for belt strength. , reduce the initial investment in equipment.

4) Reduce the maintenance of equipment. The frequency converter is an integration of electronic devices, which converts the mechanical life into the electronic life, and has a long life, which greatly reduces the amount of equipment maintenance. At the same time, the soft start process of the belt conveyor basically has no impact on the machinery industry, and also greatly reduces the maintenance of the mechanical part of the belt conveyor system. For example, after adopting the frequency converter to drive the trough belt in Wangtai No. 2 Well of Jincheng Coal Industry Group, the annual cost savings of the belt buckle alone can reach more than 10,000 yuan.

With the advancement of power electronic technology, automatic control technology and computer technology, frequency conversion speed regulation technology has developed rapidly. There are not many application examples. Mining belt conveyors are generally driven by power frequency and driven by hydraulic couplers, which have problems such as low transmission efficiency, large starting electric shock and mechanical shock, and inability to balance power, resulting in uneconomical system operation; belt and hydraulic coupling Serious wear and tear of the device, high maintenance and maintenance costs; there is reactive power circulation loss. Therefore, the use of frequency conversion control for belt conveyors is not only conducive to reducing the production cost of enterprises and improving the economic benefits of enterprises, but also in line with the theme of building a conservation-oriented society, which has very practical economic and social significance.

6) Energy saving. The energy-saving effect of using variable frequency drive on the conveyor is mainly reflected in two aspects: system power factor and system efficiency.

a. Improve the system power factor

Under normal circumstances, coal mine motors have a relatively large margin in the design process, and most of them cannot run at full load during operation. The motor works at full voltage and full speed, but the load is often small, and there is also no-load operation for part of the time. The motor has the highest efficiency and the best power factor only when it is close to full load, and decreases when it is lightly loaded, causing unnecessary power loss. This is because when the load is light, the active component of the stator current is very small, mainly the reactive component of the excitation, so the power factor is very low. After using the frequency converter to drive, the power factor is over 0.9 in the whole process, which greatly reduces the reactive power.

b. Improve system efficiency

After using the frequency converter to drive, the motor and the reducer are directly hard-connected, and the link of the hydraulic coupling is reduced in the middle. However, the transmission efficiency of the hydraulic coupler itself is not high, and it is mainly driven by liquid. The transmission efficiency of the liquid is much lower than that of the direct hard connection. Therefore, after using the inverter to drive, the total transmission efficiency of the system should be It is 5%~10% higher than the efficiency of hydraulic coupling drive.

In addition, the mine is usually far away from the substation, and the voltage fluctuates greatly in different periods. Using the automatic voltage stabilization function of the frequency converter also has some energy-saving effects. However, the voltage input range of the inverter is small, usually only 342~418V. Therefore, a high-power compensating AC voltage stabilizer is often configured at the front end of the inverter. The model specification of the voltage stabilizer can be 1.25 times that of the inverter. This ensures the safe operation of the device.