Submerged Arc Furnace

[hensa1983]

I would like to understand the electrical characteristics and operation of a ferrochrome submerged arc furnace. My particular case is that of a 37MVA furnace supplied by 3 X 12.33MVA single phase transformers pushing current into 3 electrodes. The controller uses resistance control in regulating the electrodes.

 

[7anoter4]

I am not sure if that is what you really are interested to know, but it may be useful:
"Electric submerged arc furnace" means any furnace wherein electrical energy is converted to heat energy by transmission of current between electrodes partially submerged in the furnace charge.
Ferro Chrome is produced by reducing Chrome Ore lumps and agglomerated fines known as briquettes in a submerged electric arc furnace by using carbonaceous reductants such as coke. The burden also comprises of fluxing material such as bauxite and quartz.
The electric arc furnace conducts large currents via a graphite cathode and the materials to be processed that act as an anode. The material and reagents resist the flow of current, causing it to heat up, in what is known as ohmic heating. During operation, the more dense metal separates from a variety of impurities that settle into a less dense slag on top of the metal in the furnace bath.
The plasma arc plays an important part in the drawing of electrical current and hence the delivery of thermal energy to the electric arc furnace and its contents.
Plasma is sometimes referred to as the fourth state of matter after solids, liquids and gases. Plasma is essentially partially ionized gas containing electrically neutral particles, like photons and molecules and electrically charged particles, like ions and electrons. In the presence of an electric field, the charged particles are accelerated in the direction of the field, which constitutes an electric current and hence electrical conductivity is achieved.
Like fluids, plasmas exhibit a surface tension and when in motion this surface tension acts as a membrane that generates pressure waves in the air surrounding it.
If the pressure waves fall within the audible frequency range (20 Hz - 20 kHz) our ears recognize them as sound.
Steady state melting conditions are realized by keeping the arc length (D) and arc current (Iarc) constant at a desired working point.
Currently the arc length is controlled using impedance control, where the voltage to current ratio (Varc/Iarc) is held constant at a desired working point.
A typical and detailed arc furnace structure is shown in Figure 1 .It includes a system equivalent at substation bus S, substation transformer Ts, cable run to furnace D1, power factor correction equipment C, arc
furnace transformer Ta, flexible cables D2, bus conductors B, graphite electrodes G and the melting vessel M.
In Figure 2, R1 and L1 represent the resistance and the reactance of power system at substation level, the
substation transformer winding and the cable run to the furnace transformer and the furnace transformer, and R2 and L2 represents the resistance and the reactance of the flexible cables, the bus conductors and the graphite electrodes. The dynamic variation of arc resistance and inductance is represented by Rf and Lf , and both nonlinear variables
are time varying and bounded. All the circuit parameters except the Rf and Lf can be obtained from the given conditions.

In the Lorenz model, the arc resistance is expressed as below
Rf=C1*x
C1 is a constant and x is one of the state variables[Varc for example.]
The value of arc reactance is proportional to the arc resistance with coefficient ?. i.e.
Lf=?*Rf/2?f1 where, f1 is the network frequency.
Arc current may be 1000-2000A. Arc voltage may be from 0 to 30 kV[maximum value].
The kWh/ton material for Ferro Chrome may be from 5000 up to 16000 [depending upon % chrome-less chrome more kWh/ton]
Regards