Условия и состояние электропитания дуговой печи

Electricity Environment and Conditions of Electric Arc Furnace

Electric arc furnaces used for smelting generally have three characteristic working stages:

1) The smelting cycle of an ordinary AC electric arc furnace is about 3~8 hours, depending on the power supply circuit parameters, electric furnace capacity and smelting process.

2) The melting period is about 0.5~2h, it is a three-phase asymmetric impact load, the current is extremely unstable, and the power consumption is large, accounting for about 60%~70% of the total power consumption.

3) The voltage fluctuation and power consumption during the refining period of oxidation and reduction are significantly reduced.

The working characteristics of electric arc furnaces during scrap steel smelting are:

The power factor range of the operating point of the ordinary electric arc furnace circuit is between 0.8 and 0.85; for high-power electric arc furnace, it is between 0.7 and 0.8. Lower power factor will inevitably lead to low electrical energy efficiency.

Impact of electrical energy efficiency

The waste of electric energy in electric arc furnaces is mainly reflected in two aspects. First, the power factor is low, and second, a large amount of flicker and harmonics are generated during the melting period.

Flicker is the main cause of various side effects such as harmonic distortion, voltage and current dephasing, etc. "Flicker" (Transients) is a transient distortion of current and voltage on an AC sine wave circuit.

Its main manifestations are surges, peaks, harmonics, etc. Dr. Hirschfield, a famous American energy theorist, believes that the main characteristics of this distortion are ultra-high pressure, ultra-high speed, and ultra-high frequency.

Ultra-high voltage: refers to the flicker peak being 2-50 times higher than the normal voltage amplitude, up to 500-10,000 volts.

Ultra-high speed: means that the flicker spike occurs in a very short time, and it can complete the process from bursting to disappearing in trillions (the power of two million) of a second.

Ultra-high frequency: refers to the activity of flicker spikes that are very frequent. It can be said that flicker is everywhere and every time. A light switch, the start of a household appliance, or even the click of a computer keyboard or mouse can cause dozens of flicker spikes. A flicker occurs, with a voltage as high as 500-1200 volts.

Even now, the fact that these high-voltage and high-frequency flickers are one of the causes of damage to sensitive electrical equipment has been ignored.

And on the other hand, we know that electrical power is equal to the product of current and voltage, and an instantaneous increase in voltage or current will lead to greater instantaneous power consumption.

Since the heating end of the electric arc furnace is a resistive load, these instantaneous voltages or currents cannot participate in the arc starting and heating of the electric arc furnace, and can only be distributed in the form of iron loss and line loss in the form of reactive power through feedback to the inductive load.

The inductive load in the electric arc furnace system is the transformer, and the consumption of these instantaneous reactive powers in the transformer does not make any contribution to the smelting process, which has not been considered for a long time when the electric arc furnace is working.

Ignoring for the time being the waste of electric energy caused by the low power factor of the electric arc furnace, and only considering the large number of flickers produced during the smelting and melting period, we can know that the electric energy efficiency of the electric arc furnace is relatively low compared to smooth operation (the number of flickers generated is very small) It is also lower for equipment with the same rated power.

Suppressing or reducing the number of flickers and flicker peak values generated by the electric arc furnace during the smelting and melting period, and converting this ineffective power into effective power, can not only improve the electric energy efficiency of the electric arc furnace, save electric energy, but also eliminate its impact on the power grid. impact and pollution, while protecting sensitive electrical equipment.