Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B7/00—Heating by electric discharge
  • H05B7/02—Details
  • H05B7/144—Power supplies specially adapted for heating by electric discharge; Automatic control of power, e.g. by positioning of electrodes
  • H05B7/148—Automatic control of power
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
  • G05F1/00—Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems
  • G05F1/10—Regulating voltage or current
  • G05F1/46—Regulating voltage or current wherein the variable actually regulated by the final control device is dc
  • G05F1/56—Regulating voltage or current wherein the variable actually regulated by the final control device is dc using semiconductor devices in series with the load as final control devices
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B7/00—Heating by electric discharge
  • H05B7/02—Details
  • H05B7/144—Power supplies specially adapted for heating by electric discharge; Automatic control of power, e.g. by positioning of electrodes
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/25—Process efficiency

Definitions

• the invention relates to a control device for alternating current reduction furnaces with electrodes, comprising a transformer and a control system for the controlled introduction of energy into the alternating current reduction furnaces which controls an adjustment device for the electrodes.
• Such electric reduction ovens which can be provided with six electrodes in pairwise single-phase connection or with three electrodes in Knappsack circuit or star connection, serve the production of non-ferrous metals, iron alloys and process slags.
• the control of the electrical energy input into the reduction furnace was previously by the hydraulic adjustment of the electrodes.
• the bath resistance is influenced by changing the penetration depth of the electrode into the Möller and / or arc operation - by the resistance ratios below the electrodes.
• the measured variables used here are the measured electrode currents, the impedances determined from the respective electrode currents and electrode voltages or the calculated resistances, based on the primary-side measurements of the electrical quantities.
• the adjustment of the electrode voltage is carried out in stages by changing the transmission ratio of the transformer windings by means of load tap changer.
• the furnace performance is subject to strong fluctuations in this electrode control, which is caused by continuous process-related changes in the bath resistances in immersed electrodes and / or changes in the resistance ratios in an arc operation with non-immersed electrodes become. Due to these permanent fluctuations of currents, voltages and power results in an uneven introduction of electrical energy into the furnace.
• DE 43 09 640 A1 is a DC arc furnace with a the
• Described current control loop subordinate voltage control loop wherein the actual value for the voltage regulator from the voltage applied to the converter and the reference value from the output voltage of the current regulator is formed and the voltage regulator is tuned to the flicker frequency tuned filter.
• the DC arc furnace should enable flicker-free operation even with weak supply networks - ie those with small short-circuit powers.
• DE 41 35 059 A1 relates to a device for continuous electrical voltage control, which is intended to reduce the harmonic content in the controlled voltage.
• the load voltage can be fine tuned and quickly adapted to a variable impedance.
• An AC controller used for voltage control need not be sized for the full power of the load; no current pauses arise in the load current, which are e.g. In an electric reduction furnace, a restless and unstable
• Arc operation and - because of load fluctuations - can generate a variable reactive power.
• the device is particularly suitable for the operation of electric arc furnaces, in which the load voltage must be changed quickly at a constant arc current. It varies from 100V at the beginning of the Melt, over 500 to 700 V with sufficient melt up to 1, 2 kV voltage for strong arcing.
• DE 35 08 323 C2 describes a device for feeding one or more electrodes of a single- or multi-phase electrothermal furnace via main and auxiliary transformers, which has a low network feedback, better current maintenance and - in Mehrelektrodenöfen - also an individual control of the active power under the electrodes allows.
• the current of the secondary winding is measured, rectified and supplied as a current actual value to a summer, in which the difference between the current nominal value and actual value is formed; the control deviation is supplied to a controller whose output signal is fed to a control pulse generator which generates corresponding ignition pulses for a single-phase thyristor controller, wherein the controller is connected in series with a DC link winding of the main transformer and the associated primary winding.
• Such a device is applicable to arc and reduction furnaces.
• a thyristor device provides a current control as a function of the difference between the current setpoint and the actual value of the electrode current and for a voltage regulation as a function of the voltage setpoint and the actual value of the electrode voltage, wherein the voltage regulation is slower than the current regulation and performs the adjustment of the electrodes.
• This control arrangement has been specially developed for the requirements of DC arc for steel making, in which all the electrical power is introduced in the form of an arc in the furnace for the melting process.
• the ground electrodes required in DC furnaces are exposed to extreme stress due to the problematic arrangement in the bottom of the furnace vessel.
• the bottom electrode is a weak point of the furnace and requires a complex and secure cooling. Changing the bottom electrodes is very time-consuming and cost-intensive in reduction furnaces.
• DE 28 27 875 relates to a multi-phase electric arc furnace and method for its regulation.
• the required values for the control of the secondary side of the transformer are measured and calculated from certain primary and / or secondary side measurements excluding the secondary phase voltages measured with respect to the furnace bath, the calculation of the desired control values being based on the assumption that the inductance behavior of the Secondary windings during other variations of the arc furnace is predictable, and that the control values thus calculated are subjected to certain boundary conditions in response to operational furnace variables.
• Such a device can be used in all Mehrelektrodenöfen.
• the primary-side phase voltages are measured and star currents; the secondary-side values are derived in such a way that - at least in many cases - these values can be used for better control.
• DE 20 34 874 A1 discloses an arrangement for feeding an electric arc furnace from the medium or high-voltage alternating current network in that the electrodes of the electric arc furnace are connected to the alternating current network via the furnace transformer and contactless, controllable electronic switches which regulate the furnace current and - in case of overcurrent - interrupt.
• the control should help to avoid an unbalanced load on the supply network.
• the non-contact, controllable electronic switches also replace both the step and intermediate stage switches of the furnace transformer.
• EP 0 589 544 B1 relates to a three-phase electric arc furnace with a choke connected in series and a three-phase thyristor bridge connected in parallel as a controllable bypass switch, the control in conjunction with an electronic data processing system in addition to electrical data, such as current voltage, harmonic content and flicker Process data processed and acted on target-actual data comparison.
• EP 0 498 239 B1 discloses a method for controlling the electrode of a direct-current arc furnace and electrode control device and a device in which the calculation of the setpoint value for the electrode reaction is known. bypassed in which, instead of the DC voltage, a control angle proportional signal is taken from the current controller. This signal is passed through an attenuator, which monitors not only the signal matching but also the limits and filters out unwanted frequencies.
• the setpoint corresponds to the average output of the rectifier. Irrespective of a change in voltage, the arc length adjusts itself so that the required current is achieved at a predetermined level at the rectifier; to keep the current constant, there is always sufficient control range available. Constant modulation on the rectifier also achieves a constant average power factor in the supply network.
• EP 0 429 774 A1 discloses a device and method for feeding a controlled current multiphase arc furnace consisting of a three-phase network, a controlled series reactor, a three-phase furnace transformer and an arc furnace with a hydraulically operating electrode regulation system.
• a current transformer measures the phase current and supplies it to a thyristor-controlled inductor with a control device, which in turn influences the series reactance in the main circuit. Further influencing measured signal variables are the electrode position and the transformer voltage.
• WO 02/28146 A1 describes an automatic electrode regulator based on the direct power factor regulation and a method for an electric arc furnace which has a furnace transformer, each comprising a transformer for measuring the operating current and the
• the electrical parameters of the electric reduction ovens are kept as constant as possible by the hydraulic lifting or lowering of the electrodes. However, these parameters vary permanently due to the change in the bath resistance in immersed electrodes and / or by the change in the resistance ratios in a furnace operation with non-immersed electrodes, the arc operation. This results in an uneven introduction of the electrical energy into the furnace. Furthermore, the construction of reaction spaces in the oven is made difficult by partially very strong electrode movements.
• the invention is based on the object, a control device of the type mentioned in such a way that the power input stabilized in the electric reduction furnace and thereby the energy input and production is increased. Furthermore, the electrode movements should be reduced to a minimum, so that reaction chambers can build up undisturbed.
• control device further comprises controllable power electronic AC switches, which are connected on the secondary side in the high-current conductors and connected via an ignition with the control system for supplying control ignition pulses, wherein the control device is designed such that short fluctuations of the electrical parameters can only be compensated by the AC switch.
• controllable power electronic AC switches which are connected on the secondary side in the high-current conductors and connected via an ignition with the control system for supplying control ignition pulses
• the control device is designed such that short fluctuations of the electrical parameters can only be compensated by the AC switch.
• the task of the mechanical adjustment of the electrodes is limited to the balancing of the voltage conditions of the bath voltages with coarse nominal value deviations and the compensation of electrode burn-off.
• control system has a phase control of the power semiconductor, which controls the RMS values of the secondary currents steplessly.
• control system can be designed such that it controls the RMS values of the secondary currents in reduction ovens in Knappsack- circuit.
• the power semiconductors can have antiparallel-connected thyristor sets, so that phase-angle control of the three-phase alternating current takes place.
• phase-angle control of the power semiconductors can react quickly to changes in the electrical parameters of the furnace process and stabilize the furnace performance.
• the adjusting device for the electrodes can be designed such that the voltage ratios of the bath voltages are compensated for coarse nominal value deviations and the electrode erosion. An optimal control is obtained when the current and voltage control is largely decoupled.
• the electrodes of the high-current system of the reduction furnace are connected in pairs in the star.
• the electrodes of the high-current system of the reduction furnace can be interconnected with a three-phase transformer or three single-phase transformers in Knappsack- circuit.
• control system can be designed such that the individual electrode currents for baking the Söderberg electrodes can be limited.
• control system can be embodied such that the transformer currents can be limited to avoid damage by overcurrents, in particular in the voltage range below the power break point, or the transformer power to avoid overheating and thus increase the life of the transformers, in particular in the voltage range above the current bending point is.
• the life of circuit breakers and on-load tap-changers is increased when the control system is designed such that the circuit breaker and on-load tap-changer are switchable in near de-energized state.
• the disturbances for the metallurgical reaction spaces are reduced to a minimum when the control system is designed such that additionally realized dead times and / or hystereses are provided in the adjustment of the electrodes, which promote the construction of reaction spaces below the electrodes. Frequent mechanical electrode movements to control the electrical parameters disturb these reaction spaces and hinder the metallurgical melting and reduction process.
• Fig. a six-electrode furnace with paired electrodes
• FIG. 3 shows a three-electrode furnace with a three-phase transformer in Knappsack circuit
• Fig. 5 is a set of curves for explaining the advantages of the invention.
• FIG. 1 shows a control system 1 according to the invention which has a monitor 2, a current controller 3, a phase control 4 and a voltage regulator 5. To control, for example, a personal computer 6 (PC) is connected.
• PC personal computer
• the power semiconductor 13 may include two power electronic switches connected in antiparallel, with thyristors, but also controllable power transistors, being preferably used as semiconductor components due to the large power of several MVAs. Via an ignition line 16, the power semiconductor 13 is supplied for switching through with ignition pulses by the control system 1.
• a hydraulic system 17 causes a slow electrode regulation, so that the voltage ratios of the bath voltages can be compensated for coarse setpoint deviations and the electrode consumption.
• a measuring device 18 supplies a signal corresponding to the position of the electrode 14 to the control system 1.
• measuring and monitoring devices 19 are connected to the electrical variables to which the primary voltage U PR
• the measuring and monitoring devices 19 calculate therefrom the values required for the control system 1.
• a ground fault monitoring 20 connected to the supply voltage 10, which also delivers its measured values to the control system 1.
• the control system 1 on which the invention is based can be implemented in a programmable logic controller (PLC), a process control system (PCS), a personal computer (PC) 6 or another computer-aided system.
• PLC programmable logic controller
• PCS process control system
• PC personal computer
• the input and output variables for the control system 1 are primary and secondary measuring and monitoring devices 19 for the electrical variables as well as the position of the load tap changer or the star-delta switch, if present.
• the measurement of the electrode position can be integrated into the control and regulation system 1.
• Output variables of the control system 1 are control values for the hydraulic valves for raising and lowering the electrodes 14 and the manipulated variables for the control electronics of the phase control 4 of the power semiconductors 13.
• the control system 1 can be extended by the automatic adjustment of the load tap changer of the furnace transformers 11 in order to keep the necessary control angle ⁇ and to avoid gaps in the current during arc operation and partial load.
• FIG. 2 shows a furnace 15 with six paired electrodes 14, which are connected via the power semiconductors 13 to the phases U, V, W of the secondary side of the furnace transformer 11.
• FIG. 3 shows a furnace 15 with three electrodes 14, which is connected to a three-phase transformer in a knapsack circuit.
• the structure of the high current system shown in Figure 4 shows three offset by 120 ° single-phase transformers and AC converters and an angle-symmetrical routing of the high current lines and arrangement of the electrode strands.
• the Knappsackscrien is used in electric reduction furnaces with three electrodes. With her, the connections of the secondary windings of the furnace transformers are led out and interconnected only at the three electrodes to the triangle. The three electrodes now form a star-shaped load with the furnace bath, wherein the furnace bath forms the star point. Due to the magnetic field compensating arrangement of the high-current conductor, the furnace reactance is reduced. As a result, a greater active power in relation to the transformer power can be introduced into the furnace, so that a better power factor cos ⁇ results.
• a single-phase, controllable AC converter can be used in conjunction with single-phase furnace transformers or three-phase controllable AC converters in conjunction with three-phase furnace transformers.
• the power section of the AC converters for current control is implemented per phase via two power electronic switches connected in antiparallel.
• semiconductor devices thyristors are preferably to be used due to the large power of several MVA.
• controllable power transistors is conceivable.
• the knapsack circuit shown in FIGS. 3 and 4 has the advantage of a low-reactance interconnection of the high-current lines by compensating effects of the electric fields. As a result, the generated reactive power component of the reduction furnace can be reduced.
• the respectively optimum electrode current IE can be passed through the electrode 14 in accordance with a predetermined baking program and damage to the
• Electrode 14 can be avoided by overcurrents. To avoid a fresh break of the "green" Söderberg electrode, the mechanical adjustment of the electrode 14 can be fixed.
• the transformers 11 are protected by overcurrent relays, which trigger the O- fenschalter 8 in case of overcurrents and interrupt the production operation. According to the respective voltage level, the corresponding maximum transformer current can be limited by software according to the invention by the control system 1 and thus prevent a shutdown of the transformer by overcurrent.
• the straight curve section 20 shown in FIG. 5 shows the current limitation as a function of the secondary voltage.
• FIG. 5 shows a family of curves illustrating the dependence of the secondary voltage and the secondary current on one another.
• the control system 1 By the control system 1 according to the invention, the power semiconductor 13 can be locked before switching the oven switch 8 or tap changer, so that the circuit breaker can be operated in almost de-energized state. Only the no-load current of the transformers 11 must be switched.
• the control device enables the operation of a three-electrode or three-electrode three-phase furnace without the need for a bottom electrode.
• the thyristor sets are switched in antiparallel, whereby the three-phase alternating current is maintained in phase-cut form.
• the control device on which the present invention is based is specially matched to the process requirements for electroreduction furnaces, in which electrode movements are dispensed with as far as possible, since they have a disruptive effect on the metallurgical melting and reduction process.
• the hydraulic adjustment of the electrodes should practically only compensate for electrode wear and only react to larger voltage deviations.
• bath impedance PC Personal Computer For example, bath impedance PC Personal Computer

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Plasma & Fusion (AREA)
• Power Engineering (AREA)
• Radar, Positioning & Navigation (AREA)
• General Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Automation & Control Theory (AREA)
• Discharge Heating (AREA)
• Furnace Details (AREA)
• Control Of Electrical Variables (AREA)
• Crucibles And Fluidized-Bed Furnaces (AREA)
• Ac-Ac Conversion (AREA)
• Gasification And Melting Of Waste (AREA)
• Soil Working Implements (AREA)

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Citations (10)

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• 2005
  • 2005-10-26 DE DE102005051232A patent/DE102005051232A1/de not_active Withdrawn
• 2006
  • 2006-10-11 KR KR1020077015552A patent/KR100874844B1/ko active IP Right Grant
  • 2006-10-11 CA CA2602051A patent/CA2602051C/en active Active
  • 2006-10-11 EA EA200700872A patent/EA009868B1/ru not_active IP Right Cessation
  • 2006-10-11 BR BRPI0605910-4A patent/BRPI0605910B1/pt active IP Right Grant
  • 2006-10-11 NZ NZ554958A patent/NZ554958A/en not_active IP Right Cessation
  • 2006-10-11 JP JP2007543868A patent/JP4701250B2/ja active Active
  • 2006-10-11 WO PCT/EP2006/009807 patent/WO2007048502A1/de active Application Filing
  • 2006-10-11 UA UAA200705970A patent/UA88179C2/ru unknown
  • 2006-10-11 EP EP06792415A patent/EP1808049A1/de not_active Ceased
  • 2006-10-11 CN CN200680001076XA patent/CN101099413B/zh active Active
  • 2006-10-11 AU AU2006297088A patent/AU2006297088B2/en not_active Ceased
  • 2006-10-11 US US11/884,212 patent/US20080063024A1/en not_active Abandoned
• 2007
  • 2007-04-11 NO NO20071842A patent/NO337884B1/no unknown
  • 2007-05-04 ZA ZA200703635A patent/ZA200703635B/en unknown

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