Furnace power supply device, system for power supply of an electric arc furnace or a submerged arc resistance furnace, electric arc furnace or submerged arc resistance furnace, and method of operation

Abstract

The invention discloses a furnace power supply for supplying electric energy to an electric arc furnace or a submerged arc resistance furnace, the furnace power supply being connectable to a three-phase power network, the furnace power supply being connectable to at least one electrode of the electric arc furnace or the submerged arc resistance furnace, the furnace power supply comprising a three-phase transformer having a primary circuit per phase and a secondary circuit per phase, in particular exactly one secondary circuit per phase, a rectifier circuit and - preferably - a smoothing circuit connected to the rectifier circuit, the three-phase transformer being a phase-shifting transformer.

Description

[Technical field]

[0001] The present invention relates to a furnace power supply, a system for the power supply of an electric arc furnace or a submerged arc resistance furnace, an electric arc furnace or a submerged arc resistance furnace, and a method of operation. [Background technology]

[0002] Metals, especially steels, are regularly melted and heated by electric arcs in melting units. These electrically operated melting units, especially electric arc furnaces or submerged arc resistance furnaces, operate with direct current, alternating current (AC) or three-phase AC current. Usually, for this purpose, at least one electrode is used which projects through the furnace roof into the furnace vessel, while other electrodes are provided corresponding to the first electrode or are arranged at the bottom of the melting vessel.

[0003] Electric arc furnaces or submerged arc resistance furnaces represent a highly non-linear load, which means that operation of an electric arc furnace or submerged arc resistance furnace can result in undesirable electrical network distortions on the electrical supply network, in particular flicker, harmonic currents, etc. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention is based on the task of providing an improvement or alternative to the state of the art. [Means for solving the problem]

[0005] According to a first aspect of the invention, the task is solved by a furnace power supply device for supplying electric energy to an electric arc furnace or a submerged arc resistance furnace, comprising: - the furnace power supply is connectable to a three-phase power network; the furnace power supply is connectable to at least one electrode of an electric arc furnace or a submerged arc furnace, -The furnace power supply is a three-phase transformer having a primary circuit per phase and a secondary circuit per phase, in particular exactly one secondary circuit per phase; a rectifier circuit; Preferably, the inverter comprises a smoothing circuit connected to the rectifier circuit, -Three-phase transformers are phase-shifting transformers.

[0006] The following terms are explained in more detail. Firstly, it should be clearly pointed out that in the context of this patent application, indefinite articles and numbers such as "1", "2", etc. should normally be understood as "at least" information, i.e. "at least one...", "at least two...", etc., unless it is clearly evident from the respective context or it is obvious to a person skilled in the art that they can only mean "exactly one...", "exactly two...", etc., or it is technically necessary.

[0007] In the context of this patent application, the term "particularly" should always be understood as meaning that this term introduces an optional preferential feature. This expression should not be understood as "that is to say".

[0008] An "electric arc furnace" is a furnace that uses electrical energy provided and / or processed by a "furnace power supply" to generate an electric arc to melt ingot metal, in particular scrap metal and / or scrap metal mixture and / or direct reduced iron (DRI) and / or hot briquetted iron (HBI) and / or hot metal and / or flux materials in the electric arc furnace. The electric arc furnace may be a ladle furnace.

[0009] An electric arc is formed between the charged material and the electrode. The charge in an electric arc furnace is heated both by the electric current passing through the charge and by the radiant energy emitted by the arc. Electric arc temperatures can reach approximately 3,000 °C or higher.

[0010] A "submerged arc resistance furnace" is a furnace that uses electrical energy provided and / or processed by a furnace power supply to generate an arc between an electrode and the charge material, or to heat the charge material by resistance heating (Joule effect). Charge materials are typically non-ferrous metals, ferrous alloys, waste recycle, slag and slag washing.

[0011] The electric arc furnace or submerged arc resistance furnace can have a charge capacity of 1 ton or more, preferably 20 ton or more, particularly preferably 50 ton or more. More preferably, the electric arc furnace or submerged arc resistance furnace can have a charge capacity of 100 ton or more, preferably 200 ton or more, particularly preferably 400 ton or more.

[0012] The furnace power supply can be connected to the electric arc furnace or submerged arc resistance furnace, in particular to the electrodes and / or furnace transformer of the electric arc furnace or submerged arc resistance furnace, by busbars which can be cooled with air, gas, water or another suitable cooling medium different from water or gas, by cables or other suitable power transmission media, e.g. graphite.

[0013] An "electrode" is an electrical conductor used to contact a part of a circuit, particularly an electric arc furnace or submerged arc resistance furnace circuit, particularly a non-metallic part of the circuit, which in the case of an electric arc furnace or submerged arc resistance furnace may correspond to the atmosphere within the electric arc furnace or submerged arc resistance furnace.

[0014] The electrodes may be made from high density graphite and / or Wolfram. The electrodes may be designed to transfer electrical energy that forms an arc between the tip and the charge material.

[0015] The electrodes may be pre-fired or self-fired electrodes (Soederberg electrodes), and / or extruded / composite electrodes, which are a combination of a pre-fired electrode with a Soederberg electrode as the core, and / or hollow electrode systems allowing for filling of fines through the central hole (pre-fired, self-fired), whereby the choice of electrode type may depend on the size of the electrode, the material / metallurgy to be manufactured, and economic aspects such as operating costs.

[0016] The electrodes of the electric arc furnace or submerged arc resistance furnace may be located at the top of the electric arc furnace or submerged arc resistance furnace. Preferably, the electrodes located at the top are connected to a height adjustment means, whereby the distance of the electrodes to a designated scrap and / or a designated molten metal in the electric arc furnace or submerged arc resistance furnace can be varied. Such variation can be controlled and / or adjusted by an electrode regulator.

[0017] In addition, the second electrode may be disposed within the furnace vessel of the electric arc furnace or submerged arc resistance furnace or may be a component of the interior wall of the furnace vessel.

[0018] Optionally, the second electrode may also be located at the top of the electric arc furnace or submerged arc resistance furnace, preferably connected to a height adjustment means.

[0019] It is noted specifically that the electric arc furnace or submerged arc resistance furnace may also have three, four or more electrodes.

[0020] Electric arc furnaces or submerged arc resistance furnaces can be operated with direct current or with alternating current.

[0021] In electric arc furnaces or submerged arc resistance furnaces operating with direct current, the electrodes are sometimes called anodes and cathodes. The anode can also be divided into several segments.

[0022] The anode, preferably the bottom electrode, is a metal and / or conductive material at the bottom of the furnace, and an arc is formed between the charge and a cathode from the top, preferably made of graphite or carbon.

[0023] An AC electric arc furnace or a submerged arc resistance furnace can be powered by a one-phase or a multi-phase power supply, in particular a three-phase power supply.

[0024] A "transformer" is a component that transfers electrical energy from one electrical circuit to another without a conductive connection between the two circuits. A transformer converts alternating current (AC) at the transformer's primary to AC at the transformer's secondary.

[0025] In the context of this description, the term transformer is synonymous with three-phase transformer. In other words, we always mean here a three-phase transformer. However, a three-phase transformer can also be understood as a combination of three one-phase transformers.

[0026] The transformer may have one or at least one primary circuit per phase and one or at least one secondary circuit per phase. In particular, the transformer may comprise exactly one secondary circuit per phase. The transformer may be a dry-type power transformer or an oil-cooled transformer. In particular, the transformer may also be cooled with other suitable cooling fluids or gases.

[0027] In particular, the voltage of the secondary may be 1,000V, or less than 1,000V, or more than 1,000V.

[0028] The transformer may be a high voltage to medium voltage transformer that converts a high voltage at a transformer primary to a medium voltage at a transformer secondary.

[0029] The transformer can be a high voltage to low voltage transformer that converts a high voltage at a transformer primary to a low voltage at a transformer secondary.

[0030] The transformer may be a medium voltage to medium voltage transformer that converts a medium voltage at a transformer primary to a medium voltage at a transformer secondary.

[0031] The transformer may be a medium voltage to low voltage transformer that converts a medium voltage at a transformer primary to a low voltage at a transformer secondary. The transformer may be connected to a power supply network at the transformer primary.

[0032] The high voltage can be 36 kV or more, preferably 60 kV or more, particularly preferably 100 kV or more. More advantageously, the medium voltage can be 150 kV or more, preferably 200 kV or more, particularly preferably 300 kV or more. The medium voltage can be 400 kV or less. More advantageously, the medium voltage can be 300 kV or less, preferably 200 kV or less, particularly preferably 150 kV or less.

[0033] The medium voltage can be 1 kV AC or more or 1.5 kV DC or more, preferably 2 kV or more, particularly preferably 10 kV or more. More advantageously, the medium voltage can be 15 kV or more, preferably 20 kV or more, particularly preferably 30 kV or more. The medium voltage can be 36 kV or less. More advantageously, the medium voltage can be 30 kV or less, preferably 20 kV or less, particularly preferably 15 kV or less.

[0034] The low voltage can be 50V or more, preferably 60V or more, particularly preferably 100V or more. More advantageously, the low voltage can be 120V or more, preferably 220V or more, particularly preferably 240V or more. The low voltage can be 1.000V or less, particularly preferably 900V or less. More advantageously, the low voltage can be 600V or less, preferably 240V or less, particularly preferably 220V or less. Preferably, the voltage level of the electric arc furnace or submerged arc resistance furnace can be defined according to IEC 60519-4.

[0035] A "phase-shifting transformer" is a special type of transformer that can be configured to adjust the phase relationship between its primary circuit and its secondary circuit, making it possible to control power flow on a three-phase transmission network.

[0036] The phase angles of a three-phase transformer are a function of the vector family of the three-phase transformer.

[0037] Vector groups, defined elsewhere by connection symbols, are an International Electrotechnical Commission (IEC) method of classifying the configurations of the primary, preferably the high voltage (HV) winding, and the secondary, preferably the low voltage (LV) winding of a three-phase transformer. The vector group designation indicates the winding configurations and the phase angle difference between them.

[0038] The vector family provides a simple scheme of how the transformer connections are configured. Different configurations are possible with regard to how the primary winding, preferably the MV winding, and the secondary winding, preferably the LV winding, are connected to each other. In particular, they can be connected to each other in a delta circuit, a star circuit or a zigzag circuit, whereby the primary winding, preferably the MV winding, and the secondary winding, preferably the LV winding, can each be connected differently, resulting in a phase shift between the primary and secondary of the phase-shifting transformer.

[0039] For example, a star MV winding and a delta LV winding may be combined to form a vector group, resulting in a 30 degree phase shift between the primary and secondary.

[0040] By advantageous selection of the vector group, the total harmonic distortion injected into the network can be minimized.

[0041] Total harmonic distortion (THD) can be defined as the ratio of the root mean square (RMS) amplitude of a set of harmonic frequencies to the RMS amplitude of the first harmonic or fundamental frequency. It can be calculated by the following formula:

[0042]

number

[0043] During the ceremony, THD Y = total harmonic distortion of signal Y Y h =h 次 Harmonic Amplitude Y 1,RMS = RMS value of the fundamental frequency amplitude

[0044] The electrical load on a three-phase power network during operation of an electric arc furnace or a submerged arc resistance furnace may be asymmetric, causing harmonic distortion of the three-phase power network. The total harmonic distortion of the three-phase power network can be influenced by selecting the vector group of the three-phase transformer. In particular, the total harmonic distortion caused in the three-phase power network can be minimized by using a phase-shifting transformer. A three-phase transformer can have one or more sets of secondary windings. If the transformer has several sets of secondary windings, the power can be divided between the existing sets of secondary windings. Different vector groups can be advantageously selected so that the power can be transferred with different phase offsets between the primary winding, preferably the MV winding, and each set of secondary windings, preferably the LV winding. Depending on the number of sets of secondary windings, the individual phase shifts can be advantageously selected in such a way that the harmonic course of the phases results in a simultaneous increase in the number of pulses provided. The use of more than one set of secondary windings can also improve the total harmonics of the power network.

[0045] The portion of instantaneous power that results in a net transfer of energy in one direction is known as instantaneous "real power." The portion of instantaneous power that does not result in a net transfer of energy, but instead oscillates between source and load with each cycle due to stored energy, is known as instantaneous "reactive power."

[0046] The phase angle can be influenced by the phase shift transformer within a range of primary to secondary phase shift of ±5° or less, preferably within a range of ±10° or less, particularly preferably within a range of ±15° or less. Furthermore, the phase angle can be influenced by the phase shift transformer within a range of primary to secondary phase shift of ±20° or less, preferably within a range of ±25° or less, particularly preferably within a range of ±30° or less. Furthermore, the phase angle can be influenced by the phase shift transformer within a range of primary to secondary phase shift of ±35° or less, preferably within a range of ±40° or less, particularly preferably within a range of primary to secondary phase shift of ±45° or less. The above phase shift values ​​should be understood as being read between the nearest adjacent upper or lower reversal points of the primary and phase-shifted secondary AC waveforms.

[0047] Phase shifting transformers are a simple, robust and reliable technology.

[0048] A "rectifier" is an electrical device that converts alternating current, which periodically reverses direction, into direct current, which flows in only one direction.

[0049] The rectifier circuit may be a three-phase rectifier circuit.

[0050] The rectifier circuit may have a topology including and / or consisting of diodes. The three-phase rectifier circuit may be an uncontrolled n×6 pulse diode rectifier circuit, in particular a 6 pulse diode rectifier circuit, a 12 pulse diode rectifier circuit, an 18 pulse diode rectifier circuit, etc.

[0051] The rectifier circuit can be controlled or regulated by using transistors and / or thyristors.

[0052] The rectifier can be high current fuse protected.

[0053] Drawing DC voltage from an AC source in a power supply, particularly in a furnace power supply, typically results in ripple voltage, which is a residual periodic variation.

[0054] To smooth out the ripple voltage, the rectifier circuit is connected to a "smoothing circuit" that is configured to straighten out the ripple voltage.

[0055] The smoothing circuit may include a capacitor bank connected in parallel with the rectifier circuit.

[0056] The smoothing circuit may include an inductance bank connected in series with the rectifier circuit.

[0057] Electric arc furnaces or submerged arc resistance furnaces represent highly non-linear loads that can cause flicker and / or harmonic distortion in the power network connected to the electric arc furnaces or submerged arc resistance furnaces.

[0058] It is proposed here to control, and in particular to reduce, the amount of total harmonic distortion (THD) using phase shifting transformers, which can significantly reduce grid disturbances, since THD can be minimized or prevented, and at the same time improve the efficiency of the use of the energy provided by the power network.

[0059] It is furthermore preferably proposed that a phase-shifting transformer is located between the three-phase power network and the rectifier circuit. Advantageously, this allows the furnace power supply to have a handover point between the power network and the DC bus. This allows the multipurpose usability of the furnace power supply proposed here to be achieved. In particular, the furnace power supply can be applied in combination with a chopper circuit for powering a DC-powered electric arc furnace or a DC-powered submerged arc resistance furnace according to a first variant, or in combination with an inverter circuit for powering an AC-powered electric arc furnace or an AC-powered submerged arc resistance furnace according to a second variant. Existing systems therefore do not have the modularity and multipurpose usability that can be achieved here.

[0060] In this way, a particularly advantageous modular design of the furnace power supply can be achieved which does not require separate modifications for the reduction of the total harmonic distortion.

[0061] To increase the power that can be supplied to the phases of an electric arc furnace or a submerged arc resistance furnace, the above variants of furnace power supplies can be connected together by a parallel circuit. In the case of a DC-powered electric arc furnace or a DC-powered submerged arc resistance furnace, the furnace power supplies can be connected in parallel with each other by a cathode busbar and an anode busbar.

[0062] In the parallel connection of multiple power supplies, multiple groups each including a phase shift transformer and a rectifier can be connected in parallel, which are connected to a common smoothing circuit. Furthermore, in the parallel connection of multiple power supplies, multiple groups each including a phase shift transformer, a rectifier, and a smoothing circuit can be connected in parallel.

[0063] When several furnace power supplies are connected in parallel, they are completely independent of each other, but can be interconnected by a common electronic coordination and regulation unit for individual control or regulation. Moreover, each furnace power supply of a parallel connection of several furnace power supplies can feature a different phase shift.

[0064] Depending on the number of furnace power supply devices connected in parallel, the individual phase shifts of each device can be advantageously selected in such a way that the harmonic courses of the phases result in a simultaneous increase in the number of pulses provided, which can significantly reduce the degree of total harmonic distortion caused in the power network by the operation of an electric arc furnace or a submerged arc resistance furnace.

[0065] For the operation of a multiphase electric arc furnace or a multiphase submerged arc resistance furnace, in particular a three-phase AC-fed electric arc furnace or a three-phase AC-fed submerged arc resistance furnace, a parallel connection of one of the above variants can be used, which provides a third variant of the furnace power supply, where different sub-variations are possible, whereby each subset of a single furnace power supply or a parallel arrangement of furnace power supplies can provide a phase of a multiphase system. The phase shift, expressed in radians, between each phase of a multiphase system, which is characterized by the advantageous harmonic course of the phase, can be calculated by the following formula: PS=2 * PI / N During the ceremony, PS = phase shift (radians) PI=3.141592... N = number of phases

[0066] In an arrangement for operating a multi-phase AC powered electric arc furnace or a multi-phase AC powered submerged arc resistance furnace, each phase may include an equal number of furnace power supplies connected in parallel with each other.

[0067] The modularity and versatility achieved herein can further significantly reduce maintenance and overall spare parts inventory costs.

[0068] In an advantageous embodiment, the primary of the transformer is connectable to a three-phase power network and the secondary of the transformer is directly connected to the rectifier circuit.

[0069] According to a preferred embodiment, the furnace power supply comprises an electronic control unit connectable to the electronic coordination and regulation unit, whereby the electronic control unit is operably connected to the rectifier circuit and adapted to regulate the active power flow of the furnace power supply.

[0070] The following terms are explained in more detail. An "electronic control unit" is any electronic system adapted to receive signals, and / or store signals, and / or process signals, and / or control or regulate a furnace power supply in response to at least one signal.

[0071] The furnace power supply may include one or more sensors for providing information regarding harmonic distortion and / or flicker and / or the ratio of active and reactive power flows in the power network. The electronic control unit may be operatively connected to one or more such sensors and may receive the sensor signals, process them and use them to control or regulate the furnace power supply.

[0072] The electronic control unit may be configured to control or regulate the rectifier circuit, in particular to reduce or prevent harmonic distortion and / or flicker in the power network, in particular to mitigate flicker.

[0073] The electronic control unit may be configured to control or regulate the rectifier circuit, in particular to optimise the ratio of real to reactive power flow in the power network.

[0074] The electronic control unit may be configured to control or regulate chopper or inverter circuits in the power network, in particular to reduce or prevent harmonic distortion and / or flicker, in particular to mitigate flicker, in particular by applying a pulse width modulation strategy algorithm.

[0075] A pulse-width modulation strategy algorithm (PWM) is a method of reducing the average power delivered by an electrical signal by effectively chopping the signal into discrete parts. The average value of the voltage and / or current delivered to a load can be controlled by rapidly turning on and off a switch between the power source and the load. The longer the period the switch is on compared to the off period, the greater the total power delivered to the load. This results in a discrete signal to the load. It is advantageous if the PWM switching frequency is high, especially if it is high enough so as not to affect the load. In other words, the smoother the resulting waveform perceived by the load, the better it is for the load. The speed or frequency at which the PWM switching frequency operates depends on the load.

[0076] An "electronic coordination and conditioning unit" is any electronic system adapted to communicate with one or more electronic control units. Preferably, the electronic coordination and conditioning unit is adapted to communicate with one or more electrode regulators, in particular for the purposes of reducing harmonic distortion and / or reducing flicker, in particular mitigating flicker and / or improving power factor.

[0077] The electronic coordination and regulation unit may be configured to take over higher level control or regulation of some of the connected regulators in the system of the furnace power supply, in particular one or more connected electronic control units and / or one or more electrode regulators.

[0078] The electronic coordination and regulation unit can control or regulate the voltage set points of one or several furnace power supplies.

[0079] The electronic coordination and regulation unit can control or regulate the current set points of one or several furnace power supplies.

[0080] The electronic coordination and regulation unit can control or regulate the active power setpoint of one or several furnace power supplies.

[0081] The electronic coordination and regulation unit can control or regulate the reactive power set points of one or several furnace power supplies.

[0082] The electronic coordination and regulation unit can control or regulate the frequency setpoint of one or several furnace power supplies.

[0083] The electronic coordination and regulation unit can control or regulate the impedance or resistance set points of one or several furnace power supplies.

[0084] The electronic coordination and regulation unit is capable of controlling or regulating the power factor of one or several furnace power supplies, in particular improving the power factor.

[0085] The electronic coordination and regulation unit can coordinate single electrode regulators or multi-electrode regulators of one or several AC furnace power supplies.

[0086] By controlling and / or regulating the rectifier circuit, harmonic distortion and / or flicker can be reduced.

[0087] In an optional embodiment, the furnace power supply includes a chopper circuit connected to the smoothing circuit.

[0088] The following terms are explained in more detail. A "chopper circuit" is an electronic switching circuit used to cut off one signal under the control of another signal. Chopper circuits can be used to directly convert a fixed DC input to a variable DC output voltage.

[0089] The switching elements of this chopper circuit are either fully on or fully off, so there are few losses and the chopper circuit can provide high efficiency. High switching rates of 100 Hz or more, preferably 600 Hz or more, and particularly preferably 1.000 Hz or more, can be advantageously used to stabilize the electric arc and protect the furnace power supply from possible drifts.

[0090] An "H-bridge" and / or "half H-bridge" is a well-known electronic circuit that switches the polarity of a voltage applied to a load.

[0091] The chopper circuit may comprise a half H-bridge, in particular eight half H-bridges.

[0092] The chopper circuit can be used to reduce or prevent flicker in a power network, in particular to mitigate flicker, by controlling control signals for the switches of the chopper circuit, in particular in conjunction with an electronic control unit.

[0093] Optionally, the furnace power supply comprises an inverter circuit connected to the smoothing circuit.

[0094] The following terms are explained in more detail. An "inverter circuit" is a power electronic device or circuit that changes direct current (DC) to alternating current (AC). The resulting AC frequency depends on a switching algorithm.

[0095] The inverter circuit can be controlled by applying a pulse width modulation strategy algorithm.

[0096] The inverter circuit may comprise an H-bridge, in particular four H-bridges.

[0097] The inverter circuit may be used to reduce or prevent flicker in a power network, in particular to mitigate flicker, by controlling control signals for the switches of the inverter circuit, in particular in conjunction with an electronic control unit.

[0098] According to a preferred embodiment, the rectifier circuit and / or the chopper circuit and / or the inverter circuit comprise at least one semiconductor element comprising silicon carbide.

[0099] The following terms are explained in more detail. "Semiconductor devices" include conductivity values ​​that fall between conductors, such as metallic copper, and insulators, such as glass. Semiconductor devices can be used for amplification, switching, and energy conversion.

[0100] A first embodiment of the semiconductor element is a diode.

[0101] A second embodiment of the semiconductor device is a transistor, preferably an insulated gate bipolar transistor (IGBT).

[0102] A third embodiment of the semiconductor element is a thyristor.

[0103] Advantageously, the semiconductor switches, in particular transistors or thyristors, have a switching speed of 100 Hz or more, preferably a switching speed of 600 Hz or more, particularly preferably a switching speed of 1.000 Hz or more.

[0104] The use of silicon carbide can enable a variety of advantages.

[0105] Silicon carbide can have a wide band gap of 3 eV or more, can be stably used up to a high operating temperature of 150°C, and has a particularly high thermal conductivity, in particular three times higher than that of silicon, allowing semiconductor devices made of silicon carbide to be cooled better and faster in comparison.

[0106] Furthermore, by using silicon carbide, ten times higher electric field strengths can be achieved compared to silicon, resulting in higher maximum currents and better efficiency of semiconductor devices.

[0107] Overall, a rectifier circuit and / or chopper circuit and / or inverter circuit can be achieved which has lower losses, can operate at higher ambient temperatures, thus reducing cooling requirements, and can operate at higher operating voltages and higher switching frequencies.

[0108] Furthermore, since silicon carbide is particularly insensitive to radiation, particularly the electromagnetic radiation of an electric arc furnace or a submerged arc resistance furnace, compared to other semiconductor materials, particularly silicon, higher reliability and availability of the rectifier circuit and / or chopper circuit and / or inverter circuit can be achieved when using silicon carbide.

[0109] By using silicon carbide semiconductor switches, a particularly compact and / or efficient design can be achieved.

[0110] Advantageously, the furnace power supply comprises a three-phase disconnect switch for alternating current.

[0111] The following terms are explained in more detail. A "disconnector" is a switching element that ensures that an electrical circuit is completely de-energized for service or maintenance. A three-phase disconnector has three phases.

[0112] Optionally, the furnace power supply comprises a single phase disconnect switch.

[0113] Preferably, the disconnect switch is located between a designated connection of the electrode and the inverter circuit or chopper circuit.

[0114] By means of the disconnector proposed here it can be ensured that the furnace power supply can be switched off voltage-free, so that maintenance work can be carried out safely.

[0115] Preferably, the disconnector connects the furnace power supply to ground potential in the open position, which increases the safety of maintenance operations.

[0116] Furthermore, in systems with multiple furnace power supplies, it is possible to completely isolate each furnace power supply from the rest of the system essentially without affecting the functionality of the overall system.

[0117] According to a preferred embodiment, the electric furnace power supply comprises an electronic control unit connectable to the electronic coordination and regulation unit, whereby the electronic control unit is adapted to control the active power with a current loop and / or a voltage loop and / or an impedance loop and / or an active power loop and / or a hysteresis loop of the furnace power supply.

[0118] For this purpose, the electronic control unit may be operatively connected to the rectifier circuit and / or the chopper circuit and / or the inverter circuit and may be configured to be able to influence the respective controlled variables.

[0119] Preferably, the electronic control unit uses an algorithm for a pulse width modulation strategy, preferably a synchronous, asynchronous or interleaved pulse width modulation strategy.

[0120] According to a second aspect of the invention, the task is solved by a system for supplying electrical energy to two electrodes of an electric arc furnace or a submerged arc resistance furnace, comprising: - The system can be connected to a three-phase power network; the system is connectable to electrodes of an electric arc furnace or a submerged arc resistance furnace, - a system comprising a plurality of furnace power supplies according to the first aspect of the invention, The furnace power supplies are connected in parallel with one another.

[0121] It will be appreciated that the advantages of the furnace power supply according to the first aspect of the invention, as described above, transfer directly to a system comprising a furnace power supply according to the first aspect of the invention.

[0122] In particular, to provide a higher connected load, it is advantageous to connect multiple furnace power supplies in parallel.

[0123] This approach automatically results in a greater number of phase shifting transformers and therefore advantageously also a greater number of control options for reducing harmonic distortion.

[0124] In particular, it should be borne in mind that the phase shifting transformers of the furnace power supplies may have different vector groups, and in particular each may have a different vector group.

[0125] In this way, different phase shifts can be provided by each furnace power supply, and the number of pulses provided by the system can be increased. In short, harmonic distortion can be reduced in this way.

[0126] The system can preferably have two furnace power supplies, each with a different vector group, so that the number of pulses can be doubled compared to a single furnace power supply of the same design.

[0127] The system can preferably have three furnace power supplies, each with a different vector group, so that the number of pulses can be tripled compared to a single furnace power supply of the same design.

[0128] The system can preferably have four furnace power supplies, each with a different vector group, so that the number of pulses can be quadrupled compared to a single furnace power supply of the same design.

[0129] The system can preferably have five furnace power supplies, each with a different vector group, thereby allowing the number of pulses to be five times greater compared to a single furnace power supply of the same design.

[0130] The system can preferably have six furnace power supplies, each with a different vector group, thereby allowing the number of pulses to be increased by a factor of six compared to a single furnace power supply of the same design.

[0131] For example, a system having six power supplies may be preferably configured such that a first power supply provides a phase shift such that the pulse lags the phase of the power network by 25°. Further, a second power supply may provide a phase shift such that the pulse lags the phase position of the power network by 15°. A third power supply may provide a phase shift such that the pulse lags the phase of the power network by 5°. A fourth power supply may provide a phase shift such that the pulse leads the phase of the power network by 5°. A fifth power supply may provide a phase shift such that the pulse leads the phase of the power network by 15°. A sixth power supply may provide a phase shift such that the pulse leads the phase of the power network by 25°.

[0132] In total, a harmonic distribution of 36 different pulses can be achieved, in particular 36 different pulses that can be detected after the rectifier, which is particularly advantageous for reducing harmonic distortion.

[0133] It should be expressly noted that the teachings may also be similarly adapted to different numbers of power supplies.

[0134] It should be noted that the subject matter of the second aspect may be advantageously combined with the subject matter of the preceding aspects of the invention, either individually or cumulatively in any combination.

[0135] According to a third aspect of the invention, the present task is solved by a system for supplying electrical energy to a plurality of electrodes of an electric arc furnace or a submerged arc resistance furnace, comprising: - The system can be connected to a three-phase power network; The system is connectable to a number of electrodes of an electric arc furnace or a submerged arc resistance furnace, the system comprises a plurality of systems for the supply of one electrode according to the second aspect of the invention, Each system for the supply of one electrode is connectable to one of the electrodes.

[0136] It is now proposed that a multiphase electric arc furnace or a multiphase submerged arc resistance furnace combines a plurality of systems according to the second aspect of the invention, each system according to the second aspect of the invention being connectable to exactly one electrode of the multiphase electric arc furnace or the multiphase submerged arc resistance furnace.

[0137] In particular, the system proposed herein may be advantageously used to provide power to a multi-phase AC powered electric arc furnace or a multi-phase AC powered submerged arc resistance furnace.

[0138] It will be appreciated that the advantages of the system for supplying electrical energy to one electrode of an electric arc furnace or a submerged arc resistance furnace according to the second aspect of the invention, as described above, transfer directly to a system comprising such a system according to the second aspect of the invention.

[0139] It should be noted that the subject matter of the third aspect may be advantageously combined with the subject matter of the preceding aspects of the invention, either individually or cumulatively in any combination.

[0140] According to a fourth aspect of the invention, the present task is solved by a system for supplying electrical energy to a plurality of electrodes of an electric arc furnace or a submerged arc resistance furnace, comprising: - The system can be connected to a three-phase power network; The system is connectable to a number of electrodes of an electric arc furnace or a submerged arc resistance furnace, - a system comprising a plurality of furnace power supplies according to the first aspect of the invention, a first number of at least two furnace power supplies connected in parallel with each other and connectable to the first electrode; At least one furnace power supply is connectable to the second electrode.

[0141] In particular, the system proposed herein may be advantageously used to provide power to a multi-phase AC powered electric arc furnace or a multi-phase AC powered submerged arc resistance furnace.

[0142] It will be appreciated that the advantages of the furnace power supply according to the first aspect of the invention, as described above, transfer directly to a system comprising a furnace power supply according to the first aspect of the invention.

[0143] In an advantageous embodiment, the system can be connected in star or delta configuration to the three electrodes of an electric arc furnace or a submerged arc resistance furnace.

[0144] In a preferred embodiment, the system includes electrode regulators, preferably one electrode regulator for each electrode.

[0145] The following terms are explained in more detail. The electrode may be raised and lowered automatically by a positioning system and / or by a handling system, which may use an electric winch hoist or a hydraulic cylinder or the like. The position of the electrode may be controlled and / or adjusted by an "electrode regulator". The electrode regulator may pursue different objectives individually or in combination, in particular maintaining an approximately constant voltage and / or constant current and / or power input during melting of the charge, even though the scrap may move under the electrode as it melts. The length of the arc may increase with increasing voltage supplied to the electric arc furnace or submerged arc resistance furnace.

[0146] In this way, the electrode regulator assists the system in reducing or preventing flicker in the power network, and in particular in mitigating flicker.

[0147] Conveniently, the system comprises an electronic co-ordination and regulation unit operably connected to the electronic control unit and / or the electrode regulator, preferably operably connected to each electronic control unit and / or each electrode regulator.

[0148] The electronic coordination and coordination unit advantageously allows a number of individual control and / or coordination possibilities to be used collectively to achieve the overall objective of reducing or avoiding, in particular mitigating flicker, in the power network and preferably maximizing the energy transfer to scrap the smelt.

[0149] It should be noted that the subject matter of the fourth aspect may be advantageously combined with the subject matter of the preceding aspects of the invention, either individually or cumulatively in any combination.

[0150] According to a fifth aspect of the present invention, the present task is solved by an electric arc furnace or a submerged arc resistance furnace comprising a furnace power supply device according to the first aspect of the present invention and / or a system according to the second aspect of the present invention and / or the third aspect of the present invention and / or the fourth aspect of the present invention.

[0151] It will be appreciated that the advantages of the furnace power supply arrangement according to the first aspect of the invention and / or the system according to the second aspect of the invention and / or the third aspect of the invention and / or the fourth aspect of the invention, as described above, transfer directly to an electric arc furnace or a submerged arc resistance furnace comprising a furnace power supply arrangement according to the first aspect of the invention and / or a system according to the second aspect of the invention and / or the third aspect of the invention and / or the fourth aspect of the invention.

[0152] It should be noted that the subject matter of the fifth aspect may be advantageously combined with the subject matter of the preceding aspects of the invention, either individually or cumulatively in any combination.

[0153] According to a sixth aspect of the invention the present task is solved by a method for operating an electric arc furnace or a submerged arc resistance furnace, in particular an electric arc furnace or a submerged arc resistance furnace according to the fifth aspect of the invention, in which the ratio of active and reactive power flow is controlled and / or regulated by influencing a controlled variable of a rectifier circuit, in particular the reactive power flow is minimized by influencing a controlled variable of the rectifier circuit.

[0154] It will be appreciated that the advantages of the electric arc furnace or submerged arc resistance furnace according to the fifth aspect of the invention, as described above, transfer directly to the method for operating an electric arc furnace or submerged arc resistance furnace according to the fifth aspect of the invention.

[0155] It should be noted that the subject matter of the sixth aspect may be advantageously combined with the subject matter of the preceding aspects of the invention, either individually or cumulatively in any combination.

[0156] The remaining harmonics can be further reduced or filtered by a reactor-capacitor bank connected in parallel with the furnace power supply on the same supply network.

[0157] The flicker value can be further reduced by a static reactive power compensator (SVC) or a static synchronous compensator (STATCOM) system connected in parallel with the furnace power supply on the same supply network. In an optional embodiment, the furnace power supply cooperates with an SVC or STATCOM control system. [Brief description of the drawings]

[0158] Further advantages, details and features of the invention are explained in the following description of embodiments. [Figure 1] 1 shows a schematic diagram of a first embodiment of a furnace power supply; [Diagram 2] 1 shows a schematic diagram of a second embodiment of a furnace power supply. [Diagram 3] 1 shows a schematic diagram of a third embodiment of a furnace power supply. [Figure 4] FIG. 1 shows a schematic diagram of one embodiment of a system for supplying electrical energy to one electrode of a DC-powered electric arc furnace or a DC-powered submerged arc resistance furnace. [Diagram 5] FIG. 1 shows a schematic diagram of a first embodiment of a system for supplying electrical energy to a single-phase AC powered electric arc furnace or a single-phase AC powered submerged arc resistance furnace. [Figure 6] FIG. 2 shows a schematic diagram of a second embodiment of a system for supplying electrical energy to a single-phase AC powered electric arc furnace or a single-phase AC powered submerged arc resistance furnace. [Figure 7] FIG. 1 shows a schematic diagram of one embodiment of a system for supplying electrical energy to a three-phase AC powered electric arc furnace or a three-phase AC powered submerged arc resistance furnace. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0159] In the following description, the same reference numbers respectively describe the same elements and the same features, so that a description of one element made with reference to one figure is valid for the other figures, so that repetition of the respective features is omitted.

[0160] The furnace power supply device 100 of FIG. 1 essentially comprises a transformer 200 which is a three-phase phase shifting transformer 200, a rectifier circuit 210, a smoothing circuit 220 connected to the rectifier circuit 210, and an electronic control unit 230 connected to the rectifier circuit 210.

[0161] The furnace power supply 100 is connectable to a three-phase power network 110. Furthermore, the furnace power supply 100 is connectable to two electrodes 120.

[0162] According to one embodiment, the first electrode 120 may be located at the top of a designated electric arc furnace or a designated submerged arc resistance furnace, and in particular may be connected to a height adjustment means (not shown) that is operably connected to an electrode regulator (not shown) for the first electrode 120. The second electrode 120 may be disposed within the designated electric arc furnace or the designated submerged arc resistance furnace (not shown), the second electrode being operably connected to a designated scrap (not shown) and / or a designated molten metal (not shown) within the electric arc furnace or the submerged arc resistance furnace.

[0163] The electronic control unit 230 is configured to control and / or regulate the rectifier circuit 210 .

[0164] The furnace power supply 100 of FIG. 2 further comprises an inverter circuit 240 or a chopper circuit 250, depending on whether the furnace power supply 100 is intended for use for an AC or DC powered electric arc furnace, or an AC or DC powered submerged arc resistance furnace (not shown).

[0165] The inverter circuit 240 or the chopper circuit 250 is operatively connected to an electronic control unit 230 which controls or regulates the inverter circuit 240 or the chopper circuit 250 .

[0166] The furnace power supply system 100 of FIG. 3 further includes a three-phase disconnect switch or circuit breaker 260 and / or a single-phase disconnect switch 270 .

[0167] A three-phase disconnector or circuit breaker 260 allows the furnace power supply 100 to be connected or disconnected to the three-phase power network 110. A one-phase disconnector 270 allows the furnace power supply 100 to be connected or disconnected to the electrodes 120 of an electric arc furnace or a submerged arc resistance furnace (not shown). Preferably, the disconnectors 260, 270 in the open position connect the furnace power supply to ground potential. This increases the safety of maintenance operations.

[0168] The system (not marked) for supplying electrical energy to two electrodes 120 of a DC-powered electric arc furnace or a DC-powered submerged arc resistance furnace (not shown) of FIG. 4 essentially consists of two or more furnace power supplies 100 connected in parallel with each other.

[0169] The anodes 124 of a DC powered electric arc furnace or a DC powered submerged arc resistance furnace (not shown) are connected to the multiple furnace power supplies 100 via an anode bus bar (not shown). The cathodes 122 of a DC powered electric arc furnace or a DC powered submerged arc resistance furnace (not shown) are connected to the multiple furnace power supplies 100 via a cathode bus bar (not marked).

[0170] A number of furnace power supplies 100 are connected to a three-phase power network 110 .

[0171] Furthermore, the multiple furnace power supplies 100 are connected to an electronic coordination and coordination unit 300 .

[0172] The electrode regulator 310 is connected to the electronic coordination and regulation unit 300 and is operatively connected to a height adjustment means (not shown) of the cathode 122 .

[0173] The anode 124 is located within an electric arc furnace or a submerged arc resistance furnace and is in electrical contact with a designated scrap (not shown) and / or a designated molten metal (not shown) within the electric arc furnace or the submerged arc resistance furnace (not shown).

[0174] According to an embodiment variant (not shown) of the system for supplying electrical energy to at least two electrodes of a DC-powered electric arc furnace or a DC-powered submerged arc resistance furnace according to Figure 4, the system comprises two or more cathodes, each connected to a combined or individual height adjustment means, each height adjustment means operatively connected to a separate electrode regulator. The anodes are located inside the designated electric arc furnace or the designated submerged arc resistance furnace and are in electrical contact with the designated scrap and / or the designated molten metal in the electric arc furnace or the submerged arc resistance furnace.

[0175] The system (not marked) for supplying electrical energy to two electrodes 120 of a single-phase AC powered electric arc furnace or a single-phase AC powered submerged arc resistance furnace (not shown) of FIG. 5 essentially consists of two or more furnace power supplies 100 connected in parallel with each other.

[0176] The first electrode 120 may be positioned at the top of a designated electric arc furnace or a designated submerged arc resistance furnace and may be connected to a height adjustment means (not shown) that is operably connected to an electrode regulator 310 for the first electrode 120.

[0177] The second electrode 120 is disposed within an electric arc furnace or a submerged arc resistance furnace (not shown) and is operatively connected to a designated scrap metal and / or a designated molten metal within the electric arc furnace or the submerged arc resistance furnace.

[0178] The electrode regulator 310 is connected to the electronic coordination and regulation unit 300 and is operably connected to a height adjustment means (not shown) of the first electrode 120 of a single-phase electric arc furnace or a single-phase submerged arc resistance furnace (not shown).

[0179] The system for supplying electrical energy to two electrodes 120 of a one-phase AC powered electric arc furnace or a one-phase AC powered submerged arc resistance furnace (not shown) in FIG. 6 (not marked) presents two electrodes 120, each of which is connected to a separate height adjustment means (not shown).

[0180] In this embodiment, height adjustment means allow both electrodes 120 to approach the designated scrap and / or molten metal from above in a single phase AC powered electric arc furnace or a single phase AC powered submerged arc resistance furnace. Each height adjustment means is operably connected to a respective electrode regulator 310.

[0181] In FIG. 7 , three one-phase systems (not marked) for supplying electrical energy to one electrode 120 of an AC-powered electric arc furnace or a one-phase AC-powered submerged arc resistance furnace (not shown) are connected to one another to a system (not marked) for supplying electrical energy to a three-phase AC-powered electric arc furnace or a three-phase AC-powered submerged arc resistance furnace (not marked), whereby each one-phase system (not marked) supplies one electrode 120 of the three-phase AC-powered electric arc furnace or the three-phase AC-powered submerged arc resistance furnace (not marked).

[0182] For this purpose, all furnace power supplies 100 are connected to a three-phase power network 110 .

[0183] Furthermore, all furnace power supplies 100 are connected to a combined electronic coordination and regulation unit 300 .

[0184] The three electrodes 120 may be connected together in a star or delta connection. [Explanation of symbols]

[0185] 100 Furnace power supply device 110 Three-phase power network 120 electrodes 122 Cathode 124 Anode 200 Transformer / Phase Shifting Transformer 210 Rectifier circuit 220 Smoothing circuit 230 Electronic Control Unit 240 Inverter Circuit 250 Chopper Circuit 260 Three-phase disconnector or circuit breaker 270 Single phase disconnector 300 Electronic Coordination and Coordination Unit 310 Electrode Adjuster

Claims

1. A furnace power supply (100) for supplying electrical energy to an electric arc furnace or a submerged arc resistance furnace, comprising: - said furnace power supply (100) is connectable to a three-phase power network (110); - said furnace power supply (100) is connectable to at least one electrode (120) of said electric arc furnace or said submerged arc resistance furnace, said furnace power supply (100), a three-phase transformer (200) having a primary circuit per phase and a secondary circuit per phase, in particular exactly one secondary circuit per phase, and a rectifier circuit (210), - preferably a smoothing circuit (220) connected to said rectifier circuit (210), The furnace power supply (100) is characterized in that the three-phase transformer (200) is a phase-shifting transformer (200).

2. 2. The furnace power supply (100) of claim 1, characterized in that the primary of the transformer (200) is connectable to the three-phase power network (110) and the secondary of the transformer (200) is directly connected to the rectifier circuit (210).

3. The furnace power supply (100) according to claim 1 or 2, characterized in that the furnace power supply (100) comprises an electronic control unit (230) connectable to an electronic coordination and adjustment unit (300), whereby the electronic control unit (230) is operatively connected to the rectifier circuit (210) and adapted to adjust the active power flow of the furnace power supply (100).

4. The furnace power supply (100) according to any one of claims 1 to 3, characterized in that the furnace power supply (100) comprises a chopper circuit (250) connected to the smoothing circuit (220).

5. The furnace power supply system (100) according to any one of claims 1 to 3, characterized in that the furnace power supply system (100) comprises an inverter circuit (240) connected to the smoothing circuit (220).

6. The furnace power supply device (100) according to any one of claims 1 to 5, characterized in that the rectifier circuit (210), and / or the chopper circuit (250), and / or the inverter circuit (240) comprise at least one semiconductor element comprising silicon carbide.

7. The furnace power supply device (100) according to any one of claims 1 to 6, characterized in that the furnace power supply device (100) comprises an electronic control unit (230) connectable to an electronic coordination and adjustment unit (300), whereby the electronic control unit is adapted to control an active power having a current loop and / or a voltage loop and / or an impedance loop and / or an active power loop and / or a hysteresis loop of the furnace power supply device (100).

8. A system for supplying electrical energy to two electrodes (120) of an electric arc furnace or a submerged arc resistance furnace, comprising: - said system is connectable to a three-phase power network (110); - the system is connectable to the electrodes (120) of the electric arc furnace or the submerged arc resistance furnace, The following characteristics: - the system comprises a plurality of furnace power supplies (100) according to any one of claims 1 to 7, the plurality of furnace power supplies (100) are connected in parallel with each other.

9. 1. A system for supplying electrical energy to a plurality of electrodes (120) of an electric arc furnace or a submerged arc resistance furnace, comprising: - said system is connectable to a three-phase power network (110); - the system is connectable to the electrodes (120) of the electric arc furnace or the submerged arc resistance furnace; The system comprises a plurality of systems for the supply of one electrode (120) according to claim 8, each system for the supply of one electrode (120) being connectable to one of the plurality of electrodes (120).

10. 1. A system for supplying electrical energy to a plurality of electrodes (120) of an electric arc furnace or a submerged arc resistance furnace, comprising: - said system is connectable to a three-phase power network (110); - the system is connectable to the electrodes (120) of the electric arc furnace or the submerged arc resistance furnace; The following characteristics: - the system comprises a plurality of furnace power supplies (100) according to any one of claims 1 to 7, a first number of at least two furnace power supplies (100) connected in parallel with each other and connectable to a first electrode (120); at least one furnace power supply (100) is connectable to the second electrode (120).

11. System according to any one of claims 8 to 10, characterized in that the system comprises an electrode regulator (310), preferably one electrode regulator (310) per electrode (120).

12. A system according to any one of claims 8 to 11, characterised in that the system comprises an electronic co-ordination and co-ordination unit operatively connected to the electronic control unit and / or the electrode regulator (310), preferably operatively connected to each electronic control unit and / or each electrode regulator (310).

13. An electric arc furnace or a submerged arc resistance furnace, characterized in that the electric arc furnace or the submerged arc resistance furnace comprises a furnace power supply device (100) according to any one of claims 1 to 7 and / or a system according to any one of claims 8 to 12.

14. 14. A method for operating an electric arc furnace or a submerged arc resistance furnace, in particular an electric arc furnace or a submerged arc resistance furnace, according to claim 13, characterized in that the ratio of active and reactive power flow is controlled and / or regulated by influencing a controlled variable of a rectifier circuit (210), in particular the reactive power flow is minimized by influencing a controlled variable of the rectifier circuit (210).

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