The steel industry widely used all kinds of AC-AC type, frequency conversion of the rolling mill, all kinds of roller load, electric arc furnace, converter, intermediate frequency furnace, submerged arc furnace, pressure welding machine, molten steel delivery vehicles and other equipment, their impact on power quality Great.
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Electric arc furnace load characteristics
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◆ Voltage Fluctuation and Flicker: In the early stage of smelting, the arc between electrode and charging material is very unstable, and it will be off at the same time. As a result, the power supply system works alternately in an open circuit and a loaded state, and the current intermittens. Smelting late, due to the melting of the bottom of the charge, resulting in the collapse of the upper charge, can easily lead to sudden short circuit between the electrodes, the current is small. According to statistics, electric furnace current range of up to 0 ~ 300% of the rated current furnace transformers, while the frequency range is between 0.1Hz ~ 30Hz.
◆ Low power factor: In order to restrain the voltage fluctuation and flicker, the short-circuit impedance of the electric furnace transformer is as high as 30% ~ 40% or can be used together with the series reactor. Therefore, the electric arc furnace load belongs to a typical high sense load, the power supply system power factor is very low, the typical value of 0.7 to 0.8, the limit even reached 0.1, for which companies not only need to face high fines from the electric sector, but also Lead to the extension of the smelting period, reduce production efficiency, increase active loss.
Three-phase imbalance: In the melting phase, arc furnace three-phase arc each have no regular changes, resulting in very asymmetrical three-phase current. According to statistics, the negative sequence current generated by the electric furnace load can reach 25% of the rated current of the electric furnace transformer under normal conditions, up to 56% when one phase breaks, and 86% when the two phases are short-circuited and the third phase breaks.
◆ High-order harmonics: The volt-ampere characteristics of the electric arc furnace load show a significant nonlinear relationship, which injects a large amount of harmonic current into the power grid, resulting in harmonic pollution.
According to statistics, the electric arc furnace harmonic current component to 2 to 7 times, 2,3 times the maximum, the average up to 5% of the fundamental component of 10%.
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solution
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Choose high-voltage active static var generator, filter channel generally configured 2 times, 3 times, 4 times and 5 times.
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Mill load characteristics
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◆ A typical time-varying load, active and reactive power fluctuations, easily lead to voltage fluctuations and flicker;
◆ The inverter of transmission has a large number of harmonics. If it is not governed, it will flow into the system, resulting in heating, vibration and reducing the service life of transformers, motors and cables; low power factor;
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solution
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Select high-voltage dynamic reactive power compensation device, filter channel generally configured 3 times, 5 times, 7 times and 11 times.
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Burning furnace load characteristics
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◆ Submerged arc furnace Mainly refers to smelting furnace, yellow phosphorus furnace, calcium carbide furnace, ferroalloy furnace and other major resistance-heating smelting furnace, is a huge power consumption of industrial furnace.
◆ The power factor is low; the natural power factor of most submerged arc furnaces is between 0.7 and 0.8. The lower power factor not only reduces the efficiency of the transformer, consumes a great deal of useless power, but also receives a high power penalty by the power sector.
◆ three-phase imbalance; due to the manual control of the electrode and the stacking process, resulting in increased power imbalance between the three phases, the maximum imbalance can reach more than 20%, smelting efficiency is low;
◆ Harmonic content is small, generally not more than 10%; load fluctuation is small;
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solution
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Using high-voltage passive filter device connected to the high-voltage side of the transformer or high voltage bus side of the transformer, in the compensation of reactive power but also has the function of filtering part of the harmonics, not only to meet the needs of reactive power compensation, after filtering, into the power grid harmonic Wave can reach the standard.
