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        Characteristics of power quality in coal mining industry


        Minerals is one of the more important resources of a country. China has abundant coal mines, iron ore and other resources, so China's mining industry is also relatively prosperous.
        Mining mining is inseparable from the investment of large-scale electrical equipment. The degree of qualification of electric energy directly affects the normal operation of the equipment; while many large-scale equipment work at the same time, it will have certain impact on the power system, such as power factor is not up to standard, resulting in Additional losses, currently, mainly use reactive power compensation devices to improve the power factor, while filtering some harmonics.
        Typical load and hazard

        Hoist: The hoist is equipped with a large single-machine power, which accounts for a large proportion of the total power supply load of the mine. As a high-power, frequent start, periodic impact load and the use of silicon rectifiers, the hoist causes great reactive power and high-order harmonic pollution to the power grid. Therefore, the high-power hoist puts higher demands on the capacity and stability of the power supply grid.
        Long-distance transmission lines: During the coal mining process, a large number of roadway excavation equipment, ventilation equipment, and driving light electrical equipment are applied underground. In the mining process of non-open coal mines, long transmission lines are required to provide underground equipment. Power, long-distance power transmission brings high energy consumption, resulting in low terminal voltage.
        Inverter and soft starter: The inverter or soft starter is configured to meet the requirements of improved starting shock and energy saving. Due to the use of the frequency converter, 6k±1 harmonics are generally generated.
        1, using SVG to achieve reactive power compensation
        The traditional method of improving the power factor of the coal mine industry is to add reactive compensation devices such as thyristor switching capacitors, thyristor control reactors and magnetron reactors, and use LC filters to reduce the effects of harmonic distortion, and traditional reactive power compensation. Compared with the device, SVG can dynamically compensate in real time, without over-compensation and under-compensation, which can stabilize the system voltage.
        SVG selection: The compensation capacity of SVG is generally selected according to 30% of the transformer capacity.

        2. Use APF to control harmonics
        The coal industry has frequent fluctuations in load and periodic changes, which will produce 5, 7, 11, and 13 harmonics. For the current situation of harmonics in the coal industry, the best solution for harmonic control is to use active filtering technology. In general, the active filter (controlled current source) is connected in parallel with a load generating harmonics. The current source produces a compensating current of the same magnitude as the harmonic current of the load, thereby eliminating the effects of harmonics generated by the load on the distribution network.
        APF selection:
        Active filter design capacity = operating current * current distortion rate
        Note: In order to make the compensation effect better, there is generally a margin, so the calculated capacity is generally multiplied by 1.2 as the final configured capacity.

        3. Project configuration plan

        Device name

        Installation location

        Way of governance

        Solve the problem

        Static var generator SVG load line breaker lower end centralized management Improve power factor, stabilize system voltage and reduce line loss.
        Active filter The lower end of the load line breaker is centrally managed to filter out harmonic currents and improve the reliability of the power supply system.
        Summary: After the device is put into use, it can not only ensure that the harmonic current drop of the coal mining industry is very obvious and can improve the power factor of the site. When the capacity is sufficient, the current distortion rate of the site will drop from 23% to 5%. .

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