Abstract: A method for identifying, classifying, and sending notification of an electric arc furnace's (EAF) anomalies to improve the EAF efficiency. The method includes the steps of establishing baseline state measurements of the EAF, receiving new state measurements of the EAF and statistically testing the new state measurements against the baseline state measurements. The method further includes the steps of identifying as an anomaly a failed statistical test, classifying the identified anomaly and sending notification of the classified anomaly to a configurable list of recipients.

Abstract: A system measures parameters of the electricity drawn by an arc furnace and, based on an analysis of the parameters, provides indicators of whether arc coverage has been optimized. Factors related to optimization of arc coverage include electrode position, charge level, slag level and slag behaviour. More specifically, such indicators of whether arc coverage has been optimized may be used when determining a position for the electrode such that, to an extent possible, a stable arc cavity is maintained and an open arc condition is avoided. Conveniently, by avoiding open arc conditions, the internal linings of the furnace walls and roof may be protected from excessive wear and tear.

Abstract: An electric arc furnace (EAF) including a set of mast hydraulics, a current transformer, a voltage transformer, a legacy control system and a set-point modifier. The legacy control system is in control of the set of mast hydraulics of the EAF, and receives information from the current transformer relative to current being supplied to the EAF and from the voltage transformer relative to voltage being applied to the EAF. The legacy control system using a set of set-points for the control of the set of mast hydraulics, the voltage and the current of the EAF. The set-point modifier communicates with the legacy control system, and executes the steps of: evaluating a cost function of key performance indicators of a previous heat of the EAF, the key performance indicators including electrical energy use and/or electrode consumption; and altering the set of set-points dependent upon the cost function.

Abstract: A power supply arrangement for supplying a square-wave current (I2) to a load connected to an output of the power supply arrangement, in particular a power supply arrangement in an arc furnace for generating an arc, including a transformer (TU) with at least two primary-site taps (1U1, 1U2) which form an input of the power supply arrangement, and with several secondary-side taps (2U1, 2U2, 2U3, 2UN), a bridge circuit (BU) with several first half bridges (11, 12, 13) which include converter valves (V11, V12, V13, V14, V15, V16) and which each have a first terminal (A11, A12, A13) of the bridge circuit, with a bridge section with a choke (L1), and with a second half bridge (20) which has converter valves (V17, V18) and a second terminal (A20) of the bridge circuit (BU), wherein each first terminal (A11, A12, A13) is connected to one of the secondary-side taps (2U1, 2U2, 2U3) of the transformer (TU), wherein the second terminal (A20) is connected to the output.

Abstract: A method and system automatically determines when an electrode add event occurs in an electric arc furnace having a plurality of electrode columns, each carried by an electrode positioning system. Data is received correlating to the harmonic distortion of the electrical current output to the plurality of electrode columns. Data is also received correlating to control pressures in the electrode positioning systems. Steady state control pressure data is captured when the harmonic distortion data indicates a steady state condition. An electrode add event is thereafter determined when a pressure spike is identified in the steady state control pressure data.

Abstract: A power supply system for an arc furnace includes a three phase transformer assembly, back to back SCRs coupled between a power source and the three phase transformer assembly primary windings, and three saturable-reactors, coupled between the three phase transformer assembly secondary windings and a load. A controlled DC current source is coupled between a system controller and each of said three saturable-reactors. The system controller is configured for monitoring the power source and an output current at the load, and for controlling the back-to-back SCRs and the current source.

Abstract: An apparatus for and method of controlling a remelting furnace comprising adjusting current supplied to an electrode based upon a predetermined pool power reference value and adjusting the electrode drive speed based upon the predetermined pool power reference value.

Abstract: A grating pulse compressor configuration is introduced for increasing the optical dispersion for a given footprint and to make practical the application for chirped pulse amplification (CPA) to quasi-narrow bandwidth materials, such as Nd:YAG. The grating configurations often use cascaded pairs of gratings to increase angular dispersion an order of magnitude or more. Increased angular dispersion allows for decreased grating separation and a smaller compressor footprint.

Abstract: A reactance ballast device (V), in particular for an arc furnace, has an induction coil (1) and a free-standing load stepping switch (2), with the load stepping switch (2) being designed to adjust the reactance of the induction coil (1) while on load. A transformer (T), in particular for an arc furnace (O), has an associated reactance ballast device (V) of the type mentioned initially. An arc furnace (O), in particular for steel smelting, is preceded by a transformer (T) such as this.

Abstract: A system and method for monitoring the operating parameters of an electric arc furnace having a primary electrical circuit comprising a primary current transformer. The method includes monitoring the furnace's primary current transformer; collecting data therefrom; transmitting the collected data to a server having an operatively connected monitor; and displaying the collected data on the monitor in substantially real-time. The server also collects information about the performance of the furnace from a programmable logic computer and information entered manually by an operator at a furnace monitoring viewer system, which may also be displayed in substantially real-time on the monitor.

Abstract: Aspects of the invention relate to methods and systems for predictive electrode lowering in an electric furnace. According to one aspect, there is provided a method comprising: monitoring an operating parameter of a variable reactance circuit; comparing the operating parameter with a threshold value; and lowering an electrode coupled to the variable reactance circuit if the operating parameter meets or passes the threshold value. The operating parameter may be a current threshold. The current threshold may be determined based on at least one of: a predetermined proportion of an expected total current through the variable reactance circuit; a primary supply voltage; a rated reactance value of the parallel inductor; and a target power factor. The current threshold may be in the range between about 10% and 60% of the expected total current through the variable reactance circuit and may vary proportionally with the primary supply voltage.

Abstract: A furnace's operating efficiency is improved by simultaneously monitoring various furnace operating parameters such that the monitored values may be collectively examined and correlated to determine if the furnace is sub optimally operating. In particular, the electrode current, hydraulic valve spool position, hydraulic fluid pressure, and electrode mast position of an electrical arc furnace are simultaneously monitored and correlated to determine if any unidentified sub optimal operating conditions are present. By improving the chances of detecting and correcting sub optimal operating conditions, the present invention improves the electrode consumption and overall efficiency of a furnace's operation.

Abstract: The described methods and systems may be applied to electric arc furnace installations. In this context, the method and system provide an electrode position controller coupled to the feed rate controller so as to predictively anticipate the introduction of new source material and lower the electrodes so as to prevent arc extinguishment while variable reactors are controlled to maintain predetermined power set-points. The electrode position controller may be used in place of, or in addition to, the variable reactance control system to take corrective action to address power and/or current changes or unbalances.

Abstract: A method and system for stabilizing energy consumption in multiple loads, or in single multi-phase loads. The method and system also compensates for unbalance in multi-phase loads. A central controller monitors variable reactances in the loads and identifies situations of power and/or current fluctuation and/or unbalance. It determines appropriate corrective action by the other loads/phases to compensate for the power and/or current change or unbalance due to the problematic load, and it issues control signals instructing variable reactor controllers associated with the other loads to adjust accordingly. The method and system may by applied to electric arc furnace installations. The system and method may be employed to maintain a predetermined level of unbalance in the system.

Abstract: A method and system for stabilizing energy consumption in multiple loads, or in single multi-phase loads. A central controller monitors variable reactances in the loads and identifies situations of power and/or current fluctuation and/or unbalance. The central controller determines appropriate corrective action by the other loads/phases to compensate for the power and/or current change or unbalance due to the problematic load, and it issues control signals instructing electrode position controllers associated with the other loads to adjust accordingly. The method and system may by applied to electric arc furnace installations. The electrode position controllers may be used in conjunction with variable reactance control systems to take corrective action to address power and/or current changes or unbalances. The variable reactors respond orders of magnitude faster than the electrode positioning system.

Abstract: A method and system for stabilizing energy consumption in multiple loads, or in single multi-phase loads. The method and system also compensates for unbalance in multi-phase loads. A central controller monitors variable reactances in the loads and identifies situations of power and/or current fluctuation and/or unbalance. It determines appropriate corrective action by the other loads/phases to compensate for the power and/or current change or unbalance due to the problematic load, and it issues control signals instructing variable reactor controllers associated with the other loads to adjust accordingly. The method and system may by applied to electric arc furnace installations. In this context, the method and system provide an electrode position controller coupled to the feed rate controller so as to predictively anticipate the introduction of new source material and lower the electrodes so as to prevent arc extinguishment while the variable reactors maintain predetermined power set-points.

Abstract: The electrode arrangement uses vertically oriented electrodes with side wall contacts for an electrothermic smelting furnace for aluminum production. The side wall contacts are radially moveable into the furnace to compensate for wear on the contacts. The side wall contacts can be hollow to allow a slag forming charge to be fed to the furnace.

Abstract: A furnace for growing a high volume of crystals includes a plurality of individual growth stations and first and second heater matrixes. Each individual growth station has a crucible and an insulating container generally surrounding the crucible and thermally isolating the crucible from the other individual growth stations. The first and second heater matrices each include at least two legs electrically connected in parallel and each of the legs have at least two resistance heaters electrically connected in series. Each of the individual growth stations have at least one of the resistance heaters within the first heater matrix and at least one of the resistance heaters within the second heater matrix associated therewith. The resistance heaters of the first heater matrix are located above the crucibles and are preferably adapted to provide a homogeneous temperature across tops of the crucibles.

Abstract: To re-ignite efficiently an arc-furnace arc extending between an electrode and a material to be melt, a second energy supply is provided to maintain a plasma link between the electrode and the melting material when the arc-furnace arc is interrupted The electrode is supplied by a large current power supply including a large current conductor having a self inductance and being connected to the electrode. The second energy supply is an electrical power supply wherein a high frequency bypass impedance is provided in a supply path to the large current conductor at a distance from a capacitive circuit to allow a high frequency resonant circuit to be formed by the conductor section between the capacitive circuit and the bypass impedance without adversely affecting the large current power supply of the arc furnace.

Abstract: A new control method is used to regulate the reactive power consumption of an electric arc furnace. Active and reactive power values are used space vector variables and serve as control parameter of the power source, which consists of a furnace transformer with current controllers and a booster transformer. This method helps maintain constant reactive power consumption, reduce flicker at the point of common coupling and minimize the disturbances in the power system.

Abstract: A power control system for an AC electric arc furnace. The control system includes variable reactors located intermediate a furnace power supply and arc electrodes that are height adjustable. The control system monitors operating characteristics of the furnace that are indicative of the active power consumption of the furnace and adjusts the variable reactors and the electrode height so as to minimize variations in the active power consumption. Loss of electrode arc can be predicted and countered by lowering the electrodes and decreasing the reactance of the variable reactors.

Abstract: A power control system for an AC electric arc furnace. The control system includes variable reactors located intermediate a furnace power supply and arc electrodes that are height adjustable. The control system monitors operating characteristics of the furnace that are indicative of the active power consumption of the furnace and adjusts the variable reactors and the electrode height so as to minimize variations in the active power consumption. Loss of electrode arc can be predicted and countered by lowering the electrodes and decreasing the reactance of the variable reactors.

Abstract: The invention pertains to a process and to a device for supplying current to an electric-arc melting unit for melting and heating metal, especially steel, with a three-phase a.c. source, which sends the current via devices for producing direct current or alternating current to at least one electrode projecting into the vessel of the melting unit. The three-phase a.c. source (91) is followed by at least two power supply modules (41, 4n), connected in parallel, where each power supply module (41; 4n) has an uncontrolled three-phase bridge (51, 5n), a direct-current intermediate circuit (61, 6n), and a transistor unit (71, 7n) connected in series, and where, downline from the power supply modules (41, 4n) in the current flow direction, a common current-carrying line (31) leads to at least one electrode (21) of the melting unit (11) and away from at least one other electrode (22, 24).

Abstract: An electronic-controlled furnace transformer, which enables the reactive power, consumed by the furnace to be kept constant, thus reducing flicker. This is achieved by associating with a conventional power system of the electric arc furnace with current controllers and a booster transformer. By regulating the (reactive) power input with the help of the new control method, any disturbances in the power system can be reduced to a minimum.

Abstract: A power source for an arc furnace having an intermediate circuit transformer including a magnetic decoupled booster transformer and an AC main-driven converter. Such a power source comprises a current controller and a zero voltage switch. The current controller and the zero voltage switch are integrated in the intermediate circuit transformer. The zero voltage switch short-circuits the main reactance of the booster transformer whenever the current controller faces a current cut off and is blocked.

Abstract: A temperature control system for a thermal reactor is disclosed that addresses many of the problems in the art. In accordance with one aspect of the disclosed control system, a plurality of temperature controllers are employed. Each temperature controller employs one or more dynamic models that are optimized for a given temperature range. The temperature range over which a particular controller is optimized is preferably generally exclusive of the temperature ranges over which other controllers of the plurality of temperature controllers are optimized. In accordance with another aspect of the control system, the control system employs enhanced ramp trajectory logic. In accordance with another aspect of the control system, the control system employs a virtual temperature sensor in the event of a hardware failure of the corresponding non-virtual temperature sensor.

Abstract: Controlled current feed device for electric arc furnace employed to melt metals, wherein the feed line comprises at least a medium tension bar (13), a feed control device and a transformer (17) serving the furnace, the feed control device (16) being arranged between the medium tension bar (13) and the transformer of the furnace (17) and comprising a mutual inductor (19) consisting of a primary coil (19a) and a secondary (19b) coil, the primary coil (19a) being arranged in serial connection on the feed line (10) and the secondary coil (19b) being connected to at least a re-phasing filter (20) comprising at least a condenser (22).

Abstract: An apparatus and method of controlling a remelting process by providing measured process variable values to a process controller; estimating process variable values using a process model of a remelting process; and outputting estimated process variable values from the process controller. Feedback and feedforward control devices receive the estimated process variable values and adjust inputs to the remelting process. Electrode weight, electrode mass, electrode gap, process current, process voltage, electrode position, electrode temperature, electrode thermal boundary layer thickness, electrode velocity, electrode acceleration, slag temperature, melting efficiency, cooling water temperature, cooling water flow rate, crucible temperature profile, slag skin temperature, and/or drip short events are employed, as are parameters representing physical constraints of electroslag remelting or vacuum arc remelting, as applicable.

Abstract: A method for regulation or control of the melting process in a three-phase arc furnace having at least three electrodes whose height is adjustable individually and independently of one another. Each phase of the three-phase current which feeds the three-phase arc furnace is assigned at least one electrode. The temperature of the three-phase arc furnace is monitored, particularly at points which are at risk of overheating, such as the walls of the three-phase arc furnace in the vicinity of the electrodes. When the three-phase arc furnace reaches a critical temperature in the vicinity of an electrode, the power emission from this electrode is reduced in such a manner that overheating of the three-phase arc furnace is prevented, and in that the power emission from the other electrodes or from some of the other electrodes is increased in such a manner that the total power emission from the electrodes is a maximum at a predetermined voltage.

Abstract: The present invention is a multi-faceted mobile furnace apparatus. The apparatus has a furnace system, an electrical system, a positioning system and a control unit. The furnace system has a set of movable electrodes, and at least two pour configurations, to transform a solid material into a molten state. The electrical system provides the electrode with a predetermined, yet changeable type of regulation, current, voltage, impedance, power, and/or imbalance of current. While the electrode positioning system moves the electrode, this movement determines if the electrode is properly positioned for the furnace to be an open arc system, a submerged resistance system, or submerged arc system. The above systems are monitored by the control unit. There by the furnace system, the electrical system and the positioning system can all be altered to achieve the most efficient and cost saving method to transform the solid material into the molten state.

Abstract: Method to control the power supply for electric arc furnaces, whether they be fed with AC or DC, the furnaces including a melting cycle which includes the loading of the scrap carried out at time T.sub.0, an initial step of pre-melting the scrap with low and average power with a duration of (T.sub.1 -T.sub.0), a step of melting at maximum power with a duration of (T.sub.2 -T.sub.1) and a refining step with a duration of (T.sub.3 -T.sub.2), the method including the dynamic identification of the approximate moment when situations of risk inside the furnace cease, with a consequent permission to start delivery of maximum power, the dynamic identification being governed by the control and analysis of the electrical quantities, tension and current, fed to the furnace.

Abstract: During a heating process in a three-phase, electric furnace, power can be controlled by dividing the heating process into intervals and then controlling the average power generated during each of these intervals, and by individually controlling the power generated by each phase. The latter is accomplished without requiring access to a neutral wire.

Abstract: The electrode gap of a VAR is monitored by determining the skewness of a distribution of gap voltage measurements. A decrease in skewness indicates an increase in gap and may be used to control the gap.

Abstract: A power converter device for supplying direct current to an electric arc furnace comprises at least one transformer with its primary fed with a three-phase alternating current and delivering to at least one secondary a three-phase current applied to a rectifier system outputting to the load a rectified voltage and current. The rectifier system comprises controlled semiconductors for each secondary and a freewheel circuit. The controlled semiconductors are triggered with essentially variable firing angles, modified to increase the duration of conduction in the freewheel circuit whilst reducing the duration of conduction in the triggered semiconductors, and vice versa, so as to deliver to the load a substantially constant active power or reactive power despite variations in the impedance of the load.

Abstract: When operating, DC arc furnaces generate undesired reactive load fluctuations which are compensated without special compensation reactance by a reactive power controller. As compensation reactance, use is made of inductors, which are always present and via which the arc furnace is fed by rectifiers. A current controller is connected to the rectifiers via a first summer. On the input side, the first summer is further operationally connected to the output of the reactive power controller and, as the case may be, to an AC--AC converter which supplies a signal proportional to the power supply voltage (U.sub.xN). In addition, it is possible to provide an inverter which is connected in parallel with the arc furnace on the DC side and which is operationally connected on the AC side to a feeding AC power supply network (N) via a stabilization transformer or via auxiliary windings of a furnace transformer, and to the output of the reactive power controller on the control side.

Abstract: In operation, DC arc furnaces produce reactive load fluctuations which lead to undesirable flickering phenomena especially in a frequency range from 2 Hz-20 Hz. In order to reduce these flickering phenomena, comparatively fast reactive power regulation is superimposed on slow current regulation of the DC arc furnace which is controlled by rectifiers. In consequence, the use of a reactive-power compensator to compensate for reactive power fluctuations in superfluous.

Abstract: A method for controlling temperature in thermal processing equipment having a processing chamber containing members to be processed. The method comprises the steps of heating a plurality of zones of the processing chamber by heaters provided in the zones, respectively, measuring periods of time which elapse until temperatures in the zones increase from a predetermined value to at least one reference value, obtaining time differences among the periods measured, and storing the time differences into a memory, and adjusting timings of heating the zones by the heater, thereby to reduce the time differences.

Abstract: An arc furnace (1) has an electrode (13) and connection members (14) for connection to a power-supply network (20) for supplying an arc (16) at the electrode with current. The furnace is provided with a voltage-pulse generating member (3) adapted, in connection with an interruption in the arc, to supply voltage pulses to the furnace for striking the arc.

Abstract: The present invention is an apparatus for controlling a water delivery system utilizing an instant flow tankless water heater. It includes a programmable microprocessor with support circuitry to achieve control of the outlet temperature of a varying flow rate and varying inlet temperature stream. The system senses a water outlet temperature and controls AC power through an on/off mechanism to regulate power to heating elements embedded in the water stream. The capabilities of the heating elements are improved through the application of using a microprocessor to perform a proportional (P), integrating (I) and derivative (D) calculation. The calculations are used to determine the operating characteristics of the heating system and to control the heating system.

Abstract: A power converter device for supplying direct current to an electric arc furnace comprises at least one transformer with its primary fed with a three-phase alternating current and delivering to at least one secondary a three-phase current applied to a rectifier system outputting to the load a rectified voltage and current. The rectifier system comprises controlled semiconductors for each secondary and a freewheel circuit. The controlled semiconductors are triggered with essentially variable firing angles, modified to increase the duration of conduction in the freewheel circuit whilst reducing the duration of conduction in the triggered semiconductors, and vice versa, so as to deliver to the load a substantially constant active power or reactive power despite variations in the impedance of the load.

Abstract: The direct current-electric arc furnace system includes a furnace vessel 8, one or more electric arc electrode 7 connected as a cathode, a bottom contact 12 connected as an anode, a furnace transformer 2 and a rectifier assembly 5 for feeding the furnace, an electrode control system E, and a current regulator I. A choke 6 is switched into the direct current main current circuit. A voltage control circuit F underlies the current control circuit I, whereby the output voltage of the current regulator 14 delivers the desired value for the voltage regulator 24. A filter 25 tuned to the flicker frequency follows the voltage regulator 24 with a frequency response, which is tuned to the frequency sensitivity of the human eye. Optionally, an additional control voltage signal U.sub.flick that is delivered by flicker meter can be provided to the voltage control circuit F.

Abstract: According to the present invention, there is provided a direct current electric furnace for melting metal capable of melting scraps rapidly and also capable of diminishing cold and hot spots formed on the furnace wall, wherein the direct current electric furnace is provided with a single top electrode, a plurality of furnace bottom electrodes, or a plurality of electrode units obtained by dividing a multitude of furnace bottom electrodes of a small diameter into plural units, and electric current controlling thyristor circuits for controlling each individually electric currents flowing through the plural furnace bottom electrodes or electrode units. The electric current controlling thyristor circuits may be substituted by thyristor circuits for controlling electric currents for each of plural groups obtained by dividing the above plural furnace bottom electrodes or the above many furnace bottom electrodes or the above plural electrode units into the plural groups.

Abstract: An improved arc furnace regulator employs neural circuits connected in a multi-layer network configuration with various weighted relationships between the successive layers which are automatically changed over time as a function of an error signal by means of the back-propagation method so that the regulator gradually improves its control algorithm as a result of accumulated experience. The network is implemented in software which can be developed and run on a PC with extra co-computing capability for greater execution speed. A second trainable neural network which emulates the arc furnace is used to develop the error signal, and is trained in mutually exclusive time periods with the training of the regular network.

Abstract: In a direct-current arc furnace having a bottom contact (3) which has a large area, electromagnetically produced bath agitations are influenced by an electromagnet (9) disposed underneath the vessel bottom (4) such that the natural flow in the melt bath, caused by the current flow in the melt, is reversed in direction. In this way the stability of the bottom electrode (3) is substantially increased. The electromagnet (9) is preferably integrated into the electric supply system of the furnace and serves as a smoothing choke.

Abstract: A device for coupling a flexible current feed (50) to a bottom electrode of a metallurgical vessel (10) having a first electrical coupling (20), including a second electrical coupling (30) for operatively engaging the first coupling (20), being connected to the current feed (50), a carrier element (60) and a compensating element (40) between the carrier element (60) and the second electrical coupling (30), the compensating element (40) balancing a force of the flexible current feed (50) on the first electrical coupling. The compensating element (40) may include a damper (42) in parallel to a spring (41), so that a movement of the second electrical coupling (30) with respect to the carrier element (60) is damped.

Abstract: In direct-current arc furnace the arc is deflected in a direction away from the current supply means (19) through the action of the high-current lines (18) extending under the furnace vessel. This leads to the thermal overloading of a part of the furnace vessel walls. If the high-current lines (18a) are for the major part laid in a plane above the furnace bottom, on or below the furnace platform (20), and are taken downwards to the connection fittings (10) on the furnace bottom only on the side of the furnace vessel (1) opposite the current supply means, the arc will again burn symmetrically.

Abstract: A feedback control system for the impedance control of an electric arc furnace having at least one electrode, a hydraulic electrode actuator for adjusting the electrode. The actuator is adapted to be supplied with hydraulic fluid through a control valve. The furnace further includes a controller, which is connected to the valve actuator for the control valve, and impedance signal generator for delivering impedance signals to one input of the controller and a setpoint signal generator for delivering a setpoint signal representing a desired impedance to another input of the controller.

Abstract: Method to feed a three-phase direct-arc electric furnace with controlled current and also a three-phase electric furnace thus fed for the smelting of metals, e.g.

Abstract: Two DC electric arc furnaces are provided side by side. The both DC electric arc furnaces are connected by a duct. Each of two power source apparatuses is mounted near and associated with each of the DC electric arc furnaces. The anodes of the both power source apparatuses are mutually connected by an anode cable and the cathodes of the apparatuses by a cathode cable. The anodes and the cathodes of the both DC elecric furnaces are connected to the anode cable and the cathode cable, respectively, via a connection circuit adapted to supply electric power alternately to either of the DC electric arc furnaces. When a raw material is molten in one of the DC electric arc furnaces, electric power is supplied by the both power source apparatuses to this DC electric arc furance. The exhaust gas at a high temperature produced in this DC electric arc furnace is sent to the other DC electric arc furnace through the duct and preheats another raw material charged there beforehand.

Abstract: An improved arc furnace regulator employs neural circuits connected in a multi-layer network configuration with various weighted relationships between the successive layers which are automatically changed over time as a function of an error signal by means of the back-propagation method so that the regulator gradually improves its control algorithm as a result of accumulated experience. The network is implemented in software which can be developed and run on a PC with extra co-computing capability for greater execution speed. A second trainable neural network which emulates the arc furnace is used to develop the error signal, and is trained in mutually exclusive time periods with the training of the regular network.