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        Characteristics of power quality in metallurgical industry


        The development of modern industry has become more and more demanding for metals, which has enabled the metallurgical industry to develop rapidly. The electrical equipment of metallurgical enterprises has the characteristics of large capacity, mostly inductive load, rapid load shock, high degree of automation, high degree of automation, and continuity of work;
        The electric equipment uses a large number of DC motors and converters to drive non-linear loads such as AC motor variable frequency speed control drive transformers and reactor power electronic devices.
        Metallurgical equipment such as rolling mills and electric arc furnaces cause fluctuations and flicker in the grid voltage. Three-phase unbalance, low power factor of the grid, increased line loss, and excessive harmonic content have caused harmonic hazards, which seriously endanger the safe operation and electrical system of the power system. The safe and economic operation of the equipment.
        Therefore, solving the problem of reactive power compensation and harmonic control of metallurgical power distribution system is of great significance for ensuring power quality and safe operation of power system, reducing loss and improving the efficiency of power equipment.
        Typical load
        Electric arc furnace: the nonlinearity and transient of the arc resistance will produce higher harmonics; when the AC furnace is running, due to the asymmetry of the three-phase arc, a negative sequence current will be generated;
        Refining furnace: Compared with the electric arc furnace, the furnace condition of the refining furnace is relatively stable, there is no melting period, and the active and reactive power changes are relatively stable. Although no electric arc furnace has a great influence on the power grid, there are also very good power supply quality and power equipment. Great influence
        Medium frequency furnace: The intermediate frequency furnace is a power supply device that converts the power frequency 50HZ alternating current into an intermediate frequency (300HZ to 20HZ). The three-phase power frequency alternating current is rectified into a direct current, and then the direct current is converted into an adjustable intermediate frequency current. Due to small load fluctuations, high efficiency, less reactive fluctuations; higher power factor, but a large number of harmonics.
        The harm of harmonics and reactive power to the power supply system of the metallurgical industry
        The electrical equipment of metallurgical enterprises has large capacity, most of which are inductive load, large load shock, frequent braking, rapidity, high degree of automation, and continuous work. It is a large consumer of electricity. Motor and converter drive, AC motor frequency conversion drive, transformer, reactor, power electronics and other non-linear loads. Metallurgical equipment such as rolling mills, electric arc furnaces make the grid voltage fluctuate and flicker, three-phase unbalance, grid power The factor is low, the line loss increases, and the harmonic content exceeds the standard, which has caused harmonic pollution, which seriously endangers the safe operation of the power system and the safe and economic operation of electrical equipment. Therefore, solving the problem of reactive power compensation and harmonic control of the power system is guaranteed. Power system power quality and safe operation, reduce losses, improve the output of power equipment, etc. is of great significance.

        Metallurgical industry power quality management solutions

        1, using SVG to achieve reactive power compensation
        The traditional practice of improving the reliability and power quality of the metallurgical industry is to add reactive compensation devices such as thyristor switching capacitors, thyristor control reactors and magnetron reactors, and to use LC filters to reduce the effects of harmonic distortion. Compared with the reactive power compensation device, SVG can dynamically compensate in real time, without over-compensation and under-compensation, which can stabilize the system voltage.
        2, the use of APF harmonics and three-phase imbalance management
        In the metallurgical industry, the inverter and the rectifier are included in the load. The inverter and the rectifier are typical harmonic sources, which will seriously affect the stability of the power system. For the current state of harmonics in the metallurgical industry, the best solution for harmonics and three-phase unbalance is to use active filtering. In general, the active filter (controlled current source) is connected in parallel with a harmonic-generating load. Connected, the controlled current source generates a compensating current with the same phase and opposite magnitude of the harmonic current of the load, thereby eliminating the influence of the harmonic generated by the load on the distribution network, and the principle of controlling the three-phase unbalance is similar to the harmonic control .

        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 bottom Centralized governance, local governance Improve power factor, stabilize system voltage, and reduce line loss.
        Active filter Load line breaker bottom Centralized governance, local governance Filter harmonic currents and improve the reliability of the power supply system.

        Summary: After the device is put into use, not only can the harmonic current drop of the metallurgical industry be very obvious, but also the power factor of the field can be improved. When the capacity is sufficient, the current distortion rate will be reduced from 23% to 5%.

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