Steel smelting

Load characteristics

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Iron and steel industry has the capacity of large capacity, load impact, starting from frequent, fast, continuity of work and high degree of automation characteristics. The operation of metallurgical equipment such as rolling mills, welding equipment, steel-making electric arc furnaces and intermediate frequency furnaces will cause the fluctuation of reactive power, low power factor, unbalanced three phases, increased loss and excessive harmonic content. Application of high-power variable current, variable frequency drives, large capacity up to 10,000 kilowatts, is the main power load. The harmonic interference generated by these devices during the operation of speed regulation will directly affect the power quality of the distribution system, especially during the acceleration and deceleration phases of these transmission devices. The harmonic interference is particularly serious, while the ACV system Harmonic wave not only contains the integer harmonics in the general converter device, but also contains the fundamental frequency and subharmonic sub-harmonic components, the frequency distribution of a wide range of high content, not only will cause grid voltage distortion, but also may cause the power grid in a Resonance at these frequencies must be governed.

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Harm on the steel industry hazards

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Electricity equipment in the steel industry has the characteristics of large capacity, mostly inductive load, large load impact, frequent braking, rapidity, high degree of automation and continuity of work. And the converter drive, AC motor speed control drive, transformers, reactors, power electronics and other non-linear load. Metallurgical equipment such as rolling mills, electric arc furnaces and intermediate frequency furnaces make power grid voltage fluctuate and flicker, unbalanced three phases, low power factor of power grid, increased line loss and excessive harmonic content have caused harmonic pollution and seriously endangering the safe operation of power system And electrical equipment safe and economical operation.

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Harmonic suppression and governance solutions

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1, improve electricity equipment, so that it does not produce or less produce harmonics

By the equipment structure, efficiency, cost, reliability and other factors, only part of the problem can be solved.

In 2, the series detuning reactor to suppress harmonic resonance amplification mainly suppresses the harmonic resonance amplification, the filtering effect is smaller.

3, passive filter

The traditional method of suppressing higher harmonics is to use LC passive power filters, which generally work according to the principle of resonance. It has a simple structure, a one-time low investment, low operating costs, it appears in a wide range of low-impedance impedance, can suppress multiple frequency harmonics. In absorbing high harmonics at the same time compensate for reactive power, but also has the function to improve the load power factor. However, due to the structural principle reasons, there are some shortcomings that can not be overcome in the application.

①. Due to the tuning offset and the residual resistance, the ideal condition that the impedance of the tuned filter is equal to zero is impossible. The change of the impedance greatly hinders the filtering effect and the possibility of filter overloading.

②. Can only suppress the harmonic components required by the design requirements. Sometimes due to higher harmonic components, you must also add multiple filters. This will increase the cost and size of the entire filter.

③. As the power source side of the harmonic source increases, excessive harmonic current, the filter may cause overload.

④ LC filter circuit will be due to system impedance parameters and system parallel resonance occurs, so that the device can not run.

⑤. For a special harmonic, when the system impedance and frequency changes, there may be due to parallel with the power supply impedance resonance "harmonic amplification phenomenon," the circuit does not work.

4, active filter

Huaxi Technology Active Filter (APF) basic principle is detected from the object to be compensated harmonic current, and then by the compensation device to produce a harmonic current with the same magnitude but the opposite polarity of the compensation current to eliminate harmonics in the power network Wave current, so that the grid current contains only the fundamental component.

Compared with the traditional LC filter, the advantages of the active filter are as follows:

①. To achieve a dynamic compensation, can change the frequency and amplitude of the harmonic and reactive power changes rapidly dynamic tracking compensation.

② filter characteristics from the system impedance, eliminating the danger of resonance with the system impedance.

③. Active filter output filter LCL structure access network, so that its own high-frequency carrier will not be fed back to the grid, the other systems and equipment without interference.

④. Harmonic and reactive power can be compensated at the same time, and the size of reactive power compensation can be adjusted continuously, either for a single harmonic compensation alone, but also on a number of reactive and harmonic sources of centralized compensation, cost-effective.

○ 5. When the harmonic load of the system is greater than the compensation capability of the filter, the filter can output the rated current according to the capacity of the main body and continue the effective filtering without overloading.