Electric arc furnace have the influence on electric energy efficiency

Electricity environment and status of electric arc furnace.

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

At the beginning of the melting phase, the solid charge is melted, and the energy demand is greatest.

Initial refining and heating stage

During the refining stage, the energy input at this stage only needs to balance the heat damage.

The smelting cycle of an ordinary AC electric arc furnace is about 3~8h, depending on the parameters of the power supply circuit, the capacity of the electric furnace, and the smelting process. The melting period is about 0.5~2h, which is a three-phase asymmetrical impact load, the current is extremely unstable, and the power consumption is large, accounting for about 60% to 70% of the total power consumption. During the refining period of oxidation and reduction, voltage fluctuations and power consumption are significantly reduced.

The working characteristics of electric arc furnace during scrap smelting are:

The arc frequently cuts off and re-ignites when melting begins

Arc fluctuations occur during the full melting period, and lead to rapid changes in current, collapse and short circuits.

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

The impact of power efficiency

The waste of electric energy in the electric arc furnace is mainly manifested in two aspects. One is the low power factor, and the other is a large amount of flicker and harmonics during melting.

Flicker is the main cause of many side effects such as harmonic distortion, voltage and current phase loss, etc. "Flicker" (Transients) is a transient distortion of current and voltage on AC sine wave circuits. Its main manifestations are surges, spikes, harmonics, etc. Dr. Hesfield, 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 is 2-50 times higher than the normal voltage amplitude, up to 500-10000 volts.

Ultra-high speed: refers to the flicker spike occurring in a very short period of time, it can complete the process from burst to disappear within a few trillions (the second power of a million) within a fraction of a second.

Ultra-high frequency: refers to the frequent activities of flicker spikes. It can be said that flicker is everywhere and everywhere. There are dozens of them when a light is switched on, a household appliance is started, or even a computer keyboard or mouse is clicked. A flicker occurs, and the voltage is as high as 500-1200 volts.

Even so far, the fact that thesehigh-voltage and high-frequency flickers are one of the reasons for the destruction of sensitive electrical equipment is still ignored. And on the other hand, we know that electrical work is equal to the product of current and voltage, and the instantaneous increase in voltage or current will result in greater instantaneous power consumption.

Since the heating end of the electric arc furnaceis 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 furnace system is the transformer, and the instantaneous reactive power consumption in the transformer does not contribute to the smelting process, which has not been considered for a long time when the electric arc furnace is working.

For the time being, regardless of the electric energy waste caused by the low power factor of the electric arc furnace, and only considering the large amount of flicker generated during the smelting and melting period, we can know that the electric energy efficiency of the electric arc furnace is relative to the smooth operation (the number of flickers generated is small). It is also lower for devices with the same rated power.

Suppressing or reducing the number of flickers and flicker peaks generated by the electric arc furnace during the smelting and melting period, and transforming this part of the 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 power equipment.