Power control system for AC electric arc furnace

A power control system for an AC electric arc furnace having an AC power source for applying active AC power to an arc electrode, comprising: a variable reactance intermediate the AC power source and the electrode; and a variable reactor controller for monitoring an impedance of the electrode and causing the variable reactance to vary in response to changes in the monitored electrode impedance so as to reduce variations in the active AC power provided to the electrode; the variable reactor controller is configured to calculate the electrode impedance, calculate a required reactance based on the calculated electrode impedance, and adjust the variable reactance to the calculated reactance.

A method for controlling an arc furnace having a three phase AC power source for applying three phase power to three respective arcing electrodes and having variable reactances connected intermediate respective phases of the power source and the three electrodes, comprising the steps of: a) monitoring, for each of the three power phases, a respective electrode impedance; b) calculating, for each of the three power phases, a required reactance based on the monitored electrode impedance; and c) adjusting the inductance of the variable reactances to the required reactance to compensate for variations in the respective electrode impedances so as to reduce fluctuations in an active power drawn from the power source.

An AC electric arc furnace comprising: a) a three phase power source; b) three variable reactances connected to respective phases of the three phase power source; c) a furnace transformer having primary windings and secondary windings and taps for adjusting the transformer ratio, the primary windings being connected to the three variable reactances; d) three arc electrodes connected to the secondary windings; e) a furnace vessel for receiving work material, the electrodes having arcing ends disposed within and spaced apart from the vessel, whereby application of power from the power source to the electrodes causes generation of respective electrical arcs from each of the electrodes for processing the work material; f) an electrode movement device for adjusting the height of the electrodes relative to the furnace vessel; and g) a power control system for: i) setting the transformer taps so as to match an anticipated power consumption of the furnace to a predetermined power consumption; and ii) monitoring operating characteristics of the furnace that are indicative of an active power consumption during operation of the furnace and adjusting the variable reactances and the electrode height so as to minimize variations in the active power consumption relative to the predetermined power consumption.

A power control system for an AC electric arc furnace having an AC power source for applying power to an arc electrode, comprising: an arc electrode movement device for adjusting the height of the electrode to control the arc length thereof; and an electrode position controller for controlling the operation of the electrode movement device, the position controller being configured to monitor operating characteristics of the arc furnace to predict the onset of a plurality of upset conditions and cause the electrode height to be adjusted in response to a specific predicted upset condition.

A method for controlling an AC arc furnace having an AC power source for applying power to an arcing electrode, a variable reactance connected intermediate the power source and the electrode, and an electrode movement system for adjusting the height of the electrode relative to a furnace vessel, comprising the steps of: a) monitoring a current fed to the electrode; and b) causing the electrode to be lowered and the variable reactance to be reduced when the magnitude of the monitored current decreases at a rate that exceeds a predetermined rate threshold and the magnitude of the monitored current is less than a predetermined value.

A power control system for an AC electric arc furnace having an AC power source for applying active AC power to an arc electrode, comprising: a variable reactance intermediate the AC power source and the electrode; and a variable reactor controller for monitoring an impedance of the electrode and causing the variable reactance to vary in response to changes in the monitored electrode impedance so as to reduce variations in the active AC power provided to the electrode; an electrode movement device for raising and lowering the electrode to control the length of the arc produced thereby; and an automated electrode position controller for controlling the operation of the electrode movement device, the electrode position controller being configured to monitor operating characteristics of the furnace and select from a plurality of different operating modes for controlling movement of the electrode based on the monitored operating characteristics.

A method for controlling an arc furnace having multiple phase AC power source for applying power to a plurality of arcing electrodes and having variable reactances connected intermediate respective phases of the power source and the three electrodes, comprising the steps of: a) monitoring, for each of the multiple power phases, a respective electrode impedance; b) adjusting the inductance of the variable reactances to compensate for variations in the respective electrode impedances so as to reduce fluctuations in an active power drawn from the power source; and c) monitoring the respective electrode currents to determine if the monitored currents exhibit characteristics predictive of loss of arc in the respective electrode and lowering the respective electrode and reducing the inductance of the respective variable reactor to prevent loss of arc.