Filtering device of intermediate frequency smelting furnace

Abstract

The invention relates to a filtering cabinet, and in particular relates to a filtering device of an intermediate frequency smelting furnace. The filtering cabinet comprises a controller, a switching execution mechanism and a plurality of passive filtering branches of principal character harmonic order, wherein the controller comprises a current sampling unit, a real-time current sampling value storage unit, a switching current threshold storage unit, a comparator and a data processing unit; and the controller controls step-by-step switching-on or switching-off of each passive filtering branchin accordance with the comparison result of the comparator and also controls the switching execution mechanism to switch on the passive filtering branches from low order to high order and switch off on the passive filtering branches from high order to low order. A switching strategy of the controller is determined by a load current, so all designed harmonic passive filtering branches can be ensured to switch on in a full load state, and the filtering effects are preferable.

Description

technical field [0001] The invention relates to a filter device, in particular to a filter device for an intermediate frequency melting furnace. Background technique [0002] The intermediate frequency melting furnace is a commonly used smelting equipment in the metallurgical industry. The basic principle of this equipment is that after three-phase controllable rectification, it is converted into intermediate frequency AC power and applied to the coil, and the material is heated and smelted by the principle of electromagnetic induction. The three-phase controllable rectification belongs to the 6-pulse controllable rectification, and the characteristic harmonic order generated on the grid side is 6K±1, mainly because the characteristic harmonic currents such as 5, 7, and 11 are injected into the grid to cause harmonic pollution of the grid, making the grid voltage The waveform is distorted, and the power quality is degraded, which affects the safe operation of other users' e...

AI Technical Summary

Problems solved by technology

The three-phase controllable rectification belongs to the 6-pulse controllable rectification, and the characteristic harmonic order generated on the grid side is 6K±1, mainly because the characteristic harmonic currents such as 5, 7, and 11 are injected into the grid to cause harmonic pollution of the grid, making the grid voltage The waveform is distorted and the power quality is degraded, which affects the safe operation of other users' electrical equipment and the power grid

However, traditional filter cabinets have always followed the control strategy of power factor limitation and reactive power switching. This control strategy often causes conflicts between reactive power compensation and harmonic filtering. Not in place, this is because the load of the intermediate frequency melting furnace is characterized by a generally high power factor (between 0.92 and 0.94), and the amount of reactive power compensation required to compensate the power factor of the power supply to meet the standard is relatively small, and passive filtering The capacitor capacity in the branch circuit is relatively small, but due to the large harmonic content, the 5th, 7th, and 11th harmonic currents all seriously exceed the standard, so the capacitor capacity in the passive filter branch circuit must reach a certain capacitance to meet the filtering requirements

In addition, if the fundamental reactive power of the capacitor must meet the power factor requirements of the power sector, and the cost of the filter must be acceptable to the user, according to the previous switching control strategy, the switching of the 5, 7, and 11 harmonic filter branches There will be an inconsistency between the compensated reactive power and the harmonic filtering rate. The reason is that it follows the power factor limit and the control strategy of reactive power switching. When the power factor drops and needs switching compensation, the controller follows the first high From the second to the lower order input, the opposite principle is cut out, but in this way, the harmonic filter branch of other orders cannot continue to be input, otherwise it will cause overcompensation, or the oscillation between input and cut, so the other orders of harmonics Wave filtering effect is not good

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