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Frequency control technology is widely used in mines
Sep 06, 2018

The DC speed control system of the frequency converter has been recognized as the most effective system, which can improve the speed regulation and stability, so the requirements for equipment and electric drive are very high.


1. The necessary conditions for the inverter in the mine


The information and data of coal quality in the mine are analyzed according to the design and equipment selection of the coal preparation plant. However, after the excavation of the mine, the production quantity and production quality of the original coal preparation plant have also undergone great changes. The design and equipment selection of the coal preparation plant has been successfully constructed and cannot be changed. This leads to excessive pressure on the production equipment. When the load becomes larger or smaller, the production of the entire mine is hindered, so the frequency control is used. The system is adjusted so that it can be solved perfectly. In addition, the frequency converter can also make the range of the AC motor larger and perform infinite parallel speed regulation in a larger range. During the speed regulation process, the motor condition can be checked. When the load changes, the output power is adjusted in time to ensure that the motor is in the most perfect state at all times, which improves the production efficiency of the mine, saving time and cost. .


2. Application of frequency converter in non-open mines


2.1 Mine hoist


The function of the mine hoist is to transport ore, workers and equipment. It is an important part of non-open mine transportation and is directly related to the success or failure of the entire mine. Therefore, its requirements for electric transmission are also extremely strict. The specific requirements include correct four-quadrant motion and speed regulation, rapid reversal and acceleration and deceleration, strict safety, reliability, quality and easy maintenance, fast response, accurate positioning system and braking.


The mine hoist equipment can be divided into three major aspects: wellbore inclination, lifting capacity and lifting use. The wellbore inclination is divided into shaft lifting and inclined shaft lifting. The lifting capacity is divided into cage lifting and bucket lifting, and the lifting purpose is divided into main Promotion, secondary promotion and auxiliary promotion.


The main electric drives of mine hoists include DC drive for larger mine hoists and thyristor AC for DC drive. Because both systems use DC drive, there is work. The disadvantages of low efficiency and large maintenance workload. Compared with the relatively small mine hoist, it is operated by AC electric drive. Although the electric drive is simple in structure and convenient to operate, the reaction speed is slow, the speed regulation and work efficiency are low, and the system is safe, reliable and qualified. It is inconvenient to repair and consume a lot of energy.


2.2 air compressor


The function of the air compressor is to compress the air, to drive the wind-loaded rock and the wind-driven rock drilling, etc. At the same time, the air compressor is also a very important equipment for non-open-pit mines, and its main disadvantage is that the power consumption is too large. The use of air compressors is illustrated by the following example.


There are eight air compressors in Dongrong No. 2 Mine, six of which are made in Japan and two of which are made in China. The six Japanese-made power plants are rated at 450 watts, and the rated current and rated voltage are 892 volts and 380 volts, respectively. Eight air compressors are operated in parallel. Under normal conditions, only four or five units are operated, and the remaining ones are reserved. In the initial stage of construction, air compressors were built according to the maximum displacement. However, in actual operation, the displacement and consumption of air compressors are often uncertain when the displacement and consumption are less than air. When compressing the amount, it is necessary to control the air compressor to reduce the displacement and consumption in order to adapt to the change of the new air compression. Otherwise, the pressure of the air compressor will rise continuously until it exceeds the allowable range, resulting in local equipment. The parts are overburdened and the possibility of an explosion may occur.


The air compressor of Dongrong No. 2 Mine is controlled by multi-stage pressure throttling. In order to meet the gas consumption of Dongrong No. 2 Mine, the use of air compressor is determined by the staff. The control method is Firstly, analyze the changes in time and gas consumption, and summarize which time periods have the largest amount of gas. Based on these data, the number of air compressors required for each time period is determined. Although this control can reasonably play the air compressor. Function, but there are also some relatively large shortcomings: First, the pipe network pressure is too large, in the non-open mines, the gas consumption is smaller than the gas supply, but the air compressor needs to run at full speed in order to maintain the normal work of the project. Brought a lot of power to the system. Second, the degree of tightness is not high. When the air volume changes, the air intake volume needs to withstand the fluctuation of pressure, and the wind pressure of the equipment cannot be stabilized. Third, the valve value is unstable, the valve value will be unstable after the first setting, and often changes, which increases the pressure of the pressure system, resulting in excessive consumption of the system's compressed air volume. Fourth, when the air compressor is operated in half or more of the state, the intake air flow will increase rapidly, resulting in loss of the compressed air volume, which greatly reduces the efficiency of the air compressor.


2.3 Mine ventilation


There are two forms of mine ventilation, namely synchronous and asynchronous motors. Mine ventilation generally requires a large amount of electrical voltage and a large amount of capacity. The design of mine ventilators is often built according to the maximum amount of ventilation. This results in the operation of the mines for a few years after the operation of the mines. The ventilators are operated at low loads, and the actual required ventilation during normal work. It is much smaller than the ventilation of the fan and is easy to cause waste.


2.4 Transportation System


The transportation system is divided into four types: coal feeder, scraper conveyor, belt conveyor and bucket elevator. The role of the coal feeder is to change the speed of the motor by frequency conversion, and adjust the opening of the gate to change the amount of coal. In addition, the coal feeder can also be divided into a chain coal feeder, a motor vibration coal feeder and a reciprocating machine. Three types of coal feeders. The function of the scraper conveyor is that when the frequency conversion becomes large, the transportation volume increases, the frequency conversion becomes small, and the transportation volume decreases. The role of the belt conveyor is to change the number of frequency converters in the power path, so that the frequency converter is between 0 and 100 Hz, and the actual conditions are determined by the above conditions. The role of the bucket elevator is to change the frequency of the motor to adjust the traffic.


2.5 selection of inverter


The frequency converter is the most important equipment in mine operation, and the price is relatively expensive. So how to choose the right frequency converter is also a difficult problem today. If it is not suitable, it will hinder the operation of the mine and lead to inefficient production. Excessive power consumption has caused some losses and wastes that could have been avoided, which is not conducive to development.


There are two criteria for the selection of the inverter, which are the choice of process requirements and the choice of technical specifications. The choice of process requirements needs to pay attention to the speed regulation of the motor and the safety and reliability of the inverter. The choice of technical specifications requires attention to model, power, efficiency, harmonics, rated output current and output capacity, frequency range, power supply capacity and protection.


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