Furnace power supply apparatus with a cooling system

Abstract

The invention relates to a furnace power supply apparatus (20) for the supply of an electric furnace with electric energy, wherein the furnace power supply apparatus (20) is connectable to a three-phase power network (10) and at least one electrode (30) of the electric furnace, wherein the furnace power supply apparatus (20) comprises at least one power module (100), wherein the power module (100) comprises a rectifier stage (110), connectable to a three-phase power network (10), and a converter stage (120), connectable to at least one electrode (30) of the electric furnace, wherein the furnace power supply apparatus (20) comprises at least one DC bus (130), wherein the DC bus (130) connects the rectifier stage (110) to the converter stage (120) of the at least one power module (100), wherein the furnace power supply apparatus (20) comprises a cooling system (140).

Description

[0001] Furnace power supply apparatus with a cooling system

[0002] The present invention relates to a furnace power supply apparatus with a cooling system, a furnace and a production line .

[0003] Metals , especially steel , and metal ores , are regularly melted and heated by an electric arc in an electric furnace . These electric furnaces , in particular an electric arc furnace , an electric reduction furnace , a submerged arc-resistance furnace , a ladle furnace or an open bath furnace , are operated with direct current ( DC ) , alternating current (AC ) or multiphase alternating current . Usually, at least one electrode is used for this purpose , which proj ects through the furnace roof into the furnace vessel , while the other electrodes are provided corresponding to the first electrode or are arranged in the bottom of the melting vessel .

[0004] Electric furnaces are typically operated with dedicated power supply systems in order to both supply the required amount of electrical energy as well as to mitigate the highly nonlinear loads during operation of an electric arc furnace on the electrical power network . These power supply systems therefore produce a high amount of heat losses during operation of the electric furnace which results in increased cooling requirements .

[0005] The invention is based on the problem to provide a furnace power supply apparatus with an improved cooling capability .

[0006] The problem underlying the invention is solved by an apparatus according to claim 1 . Advantageous embodiments are described in the dependent tasks . In particular, the problem underlying the invention is solved by a furnace power supply apparatus for the supply of an electric furnace with electric energy, wherein the furnace power supply apparatus is connectable to a three-phase power network and at least one electrode of the electric furnace , wherein the furnace power supply apparatus comprises at least one power module , wherein the power module comprises a recti fier stage , connectable to a three-phase power network, and a converter stage , connectable to at least one electrode of the electric furnace , wherein the furnace power supply apparatus comprises at least one DC-bus , wherein the DC-bus connects the recti fier stage to the converter stage of the at least one power module , wherein the furnace power supply apparatus comprises a cooling system .

[0007] In the following the term " intended use of the furnace power supply apparatus" is used to describe the furnace power supply apparatus being used to supply electric energy to an electric furnace during operation of the electric furnace .

[0008] A furnace power supply apparatus designed in such a way has the advantage of an improved cooling capability . In the intended use of the furnace power supply apparatus , the furnace power supply apparatus produces a high amount of heat losses . The cooling system of the furnace power supply apparatus is able to dissipate the heat losses with an increased ef ficiency .

[0009] A three-phase power network is a polyphase system used for electricity generation, transmission and distribution . A three-phase power network provides alternating current (AC ) , particularly three alternating currents , wherein each alternating current has a + 120 degree phase di f ference to one of the two other alternating currents and a - 120 degree phase di f ference to the respective other alternating current . The three-phase power network may be a high-voltage three-phase power network or a medium- voltage three-phase power network or a low-voltage three-phase power network .

[0010] High-voltage can be greater than or equal to 36 kV, pre ferably greater than or equal to 60 kV, and particularly preferably greater than or equal to 100 kV . Further advantageously, high-voltage can be greater than or equal to 150 kV, preferably greater than or equal to 200 kV, and particularly preferably greater than or equal to 300 kV . Further advantageously, high-voltage can be greater than or equal to 400 kV, preferably greater than or equal to 700 kV, and particularly preferably greater than or equal to 1100 kV .

[0011] Medium- voltage can be less than or equal to 36 kV . Further advantageously, medium- voltage can be less than or equal to 30 kV, preferably less than or equal to 20 kV, and particularly preferably less than or equal to 15 kV .

[0012] Medium- voltage can be greater than or equal to 1 kV, preferably greater than or equal to 2 kV, and particularly preferably greater than or equal to 10 kV . Further advantageously, medium-voltage can be greater than or equal to 15 kV, preferably greater than or equal to 20 kV, and particularly preferably greater than or equal to 30 kV .

[0013] Low-voltage can be greater than or equal to 50 V, preferably greater than or equal to 60 V, and particularly preferably greater than or equal to 100 V . Further advantageously, low voltage can be greater than or equal to 120 V, preferably greater than or equal to 220 V, and particularly preferably greater than or equal to 240 V . Low-voltage can be less than or equal to 1 . 000 V, and particularly preferably less than or equal to 900 V . Further advantageously, low-voltage can be less than or equal to 600 V, preferably less than or equal to 240 V, and particularly preferably less than or equal to 220 V .

[0014] Preferably, voltage levels can be defined according to IEC 60038 . Particularly preferably, voltage levels can be defined according to Table 1 , Table 3 and Table 4 of TEC 60038 .

[0015] An electric furnace can be an electric arc furnace , an electric reduction furnace , a submerged arc-resistance furnace and / or any other electric furnace suitable to melt metal or non-metal materials .

[0016] An electrode is an electrical conductor used to make contact with a part of a circuit , particularly an electric furnace , in particular a nonmetallic part of a circuit . The nonmetallic part of the circuit can correspond to the atmosphere in the electric furnace .

[0017] An electrode can be produced from high density graphite and / or Wol fram . An electrode may be designed to trans fer electrical energy forming arcs between tip and charge material . An electrode can be a prebaked electrode or a sel f-baking electrode ( Soeder- berg electrode ) and / or an extrusion / composite electrode , which is a combination of a Soederberg electrode with a prebaked electrode as a core and / or a hollow electrode system, which allows charging of fines via the center hole (prebaked, sel f-baking) , whereby the selection of the type of electrode can depend on : si ze of the electrode , produced material / metallurgy, and economic aspects such as operational costs .

[0018] An electrode of an electric furnace may be located at the top o f an electric furnace . Preferably, an electrode located at the top is connected to a height adj ustment means , whereby the distance of the electrode to the designated metal material and / or designated molten metal material in the electric furnace can be varied . Such variation can be controlled and / or regulated by an electrode regulator .

[0019] A second electrode may be disposed in a furnace vessel of an electric furnace or may be a component of the inner wall , particularly a bottom wall , of the furnace vessel .

[0020] The second electrode may also be arranged at the top of the electric furnace and preferably also be connected to a height adj ustment means .

[0021] An electric furnace may also have three , four or more electrodes . Each electrode may be connected to a height adj ustment means .

[0022] An electric furnace can be operated by means of direct current ( DC ) or by means of alternating current (AC ) .

[0023] In an electric furnace operated by means of direct current , the electrodes may be referred to as anode and cathode . A cathode may be arranged at the top of the furnace . An anode can be divided into several segments . An anode , preferably a bottom electrode , comprises metallic and / or conductive material in the bottom of a furnace and arcs are formed between the charge material and the cathode from the top, preferably a cathode made of graphite or carbon, or wol fram .

[0024] A power module is suitable or configured to supply an electric furnace with electric energy, particularly with electric energy from a three-phase power network . Preferably, a power module is suitable or configured to supply an electric furnace with electric current of appropriate current intensity and / or current strength, an electric voltage of appropriate voltage level and / or an appropriate frequency .

[0025] A power module may comprise a power module housing that limits a power module housing volume at least partially . The power module housing may comprise or be one or more cabinets , particularly switching cabinets .

[0026] A housing in the context of this invention is designed to protect components arranged inside the housing volume from external influences , in particular from mechanical and / or electrical influences and to provide a defined air condition in the housing volume , particularly a defined temperature and humidity in the housing volume . A housing may comprise a bottom part , a top part and at least one side part , preferably four side parts . The bottom part , the top part and at least one side part limit the housing volume at least partially . The bottom part , the top part and at least one side part may be connected to each other forming an integral component . Furthermore , a housing can be provided with an electrical ground connection so that the housing can increase the safety for personnel in the vicinity of the electrical components enclosed by the hous ing in a designated manner .

[0027] Two parts forming an integral component in the context of this invention are interconnected with each other by means of at least one mechanical connection . In other words , two parts forming an integral component change their relative spatial position to each other within the limits of their mechanical connection when the integral component is moved from one spatial position to another spatial position .

[0028] In a preferred embodiment of the invention, the mechanical connection of an integral component is fixed . In other words , the relative position of two parts forming an integral component , wherein the mechanical connection between the two parts is fixed, is constant during change of a spatial position of the integral component .

[0029] A recti fier stage comprises at least one recti fier circuit , preferably two or more , three or more , four or more , five or more or six or more recti fier circuits . The recti fier stage and / or the recti fier circuit is / are configured to convert an alternating current and an alternating voltage into a direct current and a direct voltage . Preferably, the recti fier stage and / or the recti fier circuit is configured to convert all phases of a multi-phase alternating current into a direct current .

[0030] The recti fier circuit may be a three-phase recti fier circuit . The three-phase recti fier circuit is configured to convert all three phases of a three-phase alternating current into a direct current .

[0031] In a preferred embodiment the rectifier circuits are connected in parallel to each other .

[0032] A recti fier circuit may comprise an uncontrolled diode bridge . A recti fier stage comprising recti fier circuits designed in such a way can also be named as Diode Front End ( DEE ) . A DEE is a unidirectional converter .

[0033] A unidirectional converter allows electric energy to flow essentially in one direction and blocks electric energy in the opposite direction . That means , electric energy can flow from a three-phase power network to a load, preferably an electric furnace , and not flow from a load to a three-phase power network . Alternatively, electric energy can flow from a load, preferably an electric furnace , to a three-phase power network and not flow from a three-phase power network to a load . A converter stage may comprise at least one inverter circuit , preferably four or more , six or more or eight or more inverter circuits . Such a converter stage is configured to convert a direct current and a direct voltage into an alternating current and an alternating voltage , preferably into a multi-phase alternating current and a multi-phase alternating voltage . The inverter circuit may be configured to convert a direct current and a direct voltage into an one-phase alternating current and into an one-phase alternating voltage .

[0034] In a preferred embodiment , the inverter circuit is a three-phase inverter circuit . The three-phase inverter circuit is configured to convert a direct current and a direct voltage into a three-phase alternating current and a three-phase alternating voltage . Each alternating current of the three-phase alternating current may have a + 120 degree phase di f ference to one of the two other alternating currents and a - 120 degree phase di f ference to the respective other alternating current .

[0035] In a preferred embodiment the inverter circuits of a converter stage are connected in parallel to each other .

[0036] A recti fier circuit and / or an inverter circuit may comprise a plurality of switching devices connected in parallel and / or series to each other, wherein the switching devices may comprise semi-conductors , diodes , thyristors such as Silicon Controlled Recti fiers ( SCR) , Gate Turn-Of f thyristors ( GTO) , Integrated Gate-Commutated Thyristors ( IGCT ) , Metal-Oxide Semiconductor Controlled Thyristors (MCT ) , transistors such as Bipolar Junction Transistors (BJT ) , Metal-Oxide Semiconductor Field-Ef fect Transistors (MOSFET ) and / or Insulated-Gate Bipolar Transistor ( IGBT ) .

[0037] A recti fier stage and / or a converter stage may be a bidirectional converter . A bidirectional converter allows electric energy to flow essentially in both directions , that means , electric energy can flow from a three-phase power network to a load, preferably an electric furnace , and from a load, preferably an electric furnace , to a three-phase power network .

[0038] A bidirectional recti fier stage may also be named as Active Front End (AFE ) .

[0039] A switching device may be an integral component , particularly an integral component comprising a switching device housing . The switching device housing may be fluid tight . The switching device housing may comprise a cylindrical shape and / or a cuboid shape . The switching device housing may comprise metal material and / or plastic material and / or ceramic material . Particularly, the switching device housing may comprise a first surface and a second surface opposite to the first surface . The first surface and / or the second surface may comprise or consist of metal material and / or plastic material . The remaining surfaces may comprise or consist of plastic material and / or ceramic material . In case of a cylindrical shaped switching device housing, the first surface and the second surface correspond to the circular surfaces of the cylinder and the remaining surface corresponds to the outer surface of a cylinder .

[0040] The first surface and the second surface of a switching device housing may be configured to conduct electrical energy, particularly electrical current , particularly electrical energy from a three-phase power network to an electric furnace and / or electrical energy from an electric furnace to a three-phase power network . In the intended use of the furnace power supply apparatus , the first surface and the second surface of a switching device housing may be under electrical voltage . A switching device may comprise one or more press-packed IGBTs or may be a press-packed IGBT . In an alternative intended use of the furnace power supply apparatus , the switching device housing is electrically isolated . Particularly, a switching device , preferably a switching device housing, may be electrically isolated with respect to the power module housing . In other words , the switching device and / or the switching device housing may comprise a floating potential with respect to the power module housing . A floating potential in the context of this invention means , that the switching devices and / or the switching device housings are at least partially isolated with respect to the power module housing . That is , they are electrically isolated with regard to the power module housing and therefore to the electrical ground, thereby preventing or at least considerably limiting the generation of parasitic current to the electrical ground connection .

[0041] The switching device housing may comprise at least one cooling surface , particularly two cooling surfaces . In a preferred embodiment , the first surface and / or the second surface are configured as cooling surface .

[0042] A recti fier circuit and / or an inverter circuit may each be an integral component , particularly an integral component formed by a plurality of switching devices connected electrically in parallel and / or series to each other, wherein the switching devices are mechanically connected at least indirectly to each other .

[0043] In a preferred embodiment , the switching devices of one recti fier circuit are stacked vertically and / or hori zontally to each other .

[0044] Preferably, the switching devices of one recti fier circuit are stacked vertically and / or hori zontally to each other and spaced apart from each other . In other words , there is a clearance between the vertically and / or hori zontally stacked switching devices of one recti fier circuit . Alternatively, the switching devices of one recti fier circuit are in direct contact with each other, further preferred in direct surface contact with each other .

[0045] Further preferred, the stacked switching devices of one rectifier circuit are arranged in a frame structure .

[0046] The frame structure may comprise a first frame end plate and a second frame end plate and at least one connection element , preferably four connection elements , mechanically connecting the first frame end plate and the second frame end plate to each other . The switching devices , preferably the vertically and / or hori zontally stacked switching devices , may be arranged between the first frame end plate and the second frame endplate . In thi s way, the switching devices and the frame structure form an integral component . In other words , the recti fier circuit forms an integral component .

[0047] In a preferred embodiment the switching devices of one inverter circuit are stacked vertically and / or hori zontally to each other .

[0048] Preferably, the switching devices of one inverter circuit are stacked vertically and / or hori zontally to each other and spaced apart from each other . In other words , there is a clearance between the vertically and / or hori zontally stacked switching devices of one inverter circuit . Alternatively, the switching devices of one inverter circuit are in direct contact with each other, further preferred in direct surface contact with each other .

[0049] Further preferred, the stacked switching devices of one inverter circuit are arranged in a frame structure . The frame structure may comprise a first frame end plate and a second frame end plate and at least one connection element , preferably four connection elements , mechanically connecting the first frame end plate and the second frame end plate to each other . The switching devices , preferably the vertically or hori zontally stacked switching devices , may be arranged between the first frame end plate and the second frame endplate . In this way, the switching devices and the frame structure form an integral component . In other words , the inverter circuit forms an integral component .

[0050] The connection elements may mechanically connect the first frame end plate and the second frame end plate and apply a compressive force on the first frame end plate , on the second frame end plate and on the stacked switching devices , particularly on the stacked switching device housings , arranged in between them . The connection elements may be connection rods , bolts , screws or the like .

[0051] The recti fier stage and / or the converter stage may be arranged in the power module housing .

[0052] The recti fier stage may comprise a plurality of frame structures of switching devices . The plurality of frame structures of switching devices may be stacked vertically and / or hori zontally to each other .

[0053] The converter stage may comprise a plurality of frame structures of switching devices . The plurality of frame structures of switching devices may be stacked vertically and / or hori zontally to each other .

[0054] Alternatively, a converter stage may comprise at least one DC-chopper circuit , preferably two or more , three or more , four or more , five or more or six or more DC-chopper circuits . A DC-chopper circuit is configured to convert a direct current with a fixed voltage level to a direct current with a variable voltage level directly . Such a converter stage is configured to convert a direct current with a fixed voltage level to a direct current with a variable current and voltage level directly .

[0055] In a preferred embodiment the DC-chopper circuits are connected in parallel and / or series to each other .

[0056] Since a switching device in a DC-chopper circuit is either fully on or fully of f , its losses are low and a DC-chopper circuit can provide high ef ficiency, with a switching rate of higher than or equal to 1 kHz , preferably higher than or equal to 2 kHz and particularly preferably higher than or equal to 5 kHz . Advantageously, a DC-chopper circuit may have a switching rate higher than or equal to 10 kHz , preferably higher than or equal to 15 kHz and particularly preferably higher than or equal to 20 kHz . In this way, an electric arc can advantageously be stabili zed while the furnace power supply apparatus can at the same time be protected from a possible dri ft .

[0057] A DC-chopper circuit may comprise a plurality of switching devices connected in parallel and / or series to each other wherein the switching devices comprises semi-conductors , diodes , thyristors such as Silicon Controlled Recti fiers ( SCR) , Gate Turn- Of f thyristors ( GTO) , Integrated Gate-Commutated Thyristors ( IGCT ) , Metal-Oxide Semiconductor Controlled Thyristors (MCT ) , transistors such as Bipolar Junction Transistors (BJT ) , Metal- Oxide Semiconductor Field-Ef fect Transistors (MOSFET ) and / or Insulated-Gate Bipolar Transistor ( IGBT ) .

[0058] A DC-chopper circuit may be galvanically isolated . Particularly, a DC-chopper circuit may comprise at least one power conducting element , wherein the power conducting element provides a galvanic isolation . The power conducting element may be an inductive element , particularly magnetic coil . Further particularly, the DC-chopper circuit may comprise two magnetic coils . The power conducting element may be a trans former .

[0059] A DC-chopper circuit may be a bidirectional DC-chopper circuit . Alternatively, a DC-chopper circuit may be a unidirectional DC-chopper circuit .

[0060] A DC-chopper circuit may be configured as a Fly-Back-Converter, as a Forward Converter or as a Push-Pull Converter .

[0061] A DC-chopper circuit may be an integral component . In a preferred embodiment , the DC-chopper circuit comprises a plurality of switching devices , wherein each switching device is mounted on a j oint heat sink .

[0062] The DC bus may comprise one or more capacitors and / or coils connected in series and / or parallel to each other to store energy and create an electrical separation between the recti fier stage and the converter stage . An electrical separation may be achieved through electrical energy stored in the DC bus and / or its capacitors and / or coils . The electrical separation stored can absorb fluctuations , particularly instantaneous fluctuations , in electrical energy supply and / or demand .

[0063] The DC bus may comprise or cons ist of power cables and / or bus bars . The DC bus may be part of the power module . The DC bus may be arranged in the power module housing .

[0064] Preferably, the power module may comprise a plurality of DC busses connected in parallel to each other . Particularly, one DC bus connects exactly one recti fier circuit with one inverter circuit or DC-chopper circuit . In other words , there is a one to one connection between a recti fier circuit , a DC bus and an inverter circuit or a DC-chopper circuit . Further expressed in other words , one DC bus is connected to only one recti fier circuit and to only one inverter circuit or DC-chopper circuit .

[0065] The power module may comprise a DC / DC converter circuit connected to the recti fier stage . Particularly the DC / DC converter circuit may be connected to the recti fier stage via the DC bus . In a preferred embodiment , the furnace power supply apparatus may comprise two DC busses , wherein a first DC bus connects the recti fier stage to the DC / DC converter circuit and a second DC bus connects the DC / DC converter circuit to the converter stage of the power module . In other words , the two DC busses are connected in series to each other .

[0066] A DC / DC converter circuit is an electrical device that converts a direct current with a first voltage level into a direct current with a second voltage level .

[0067] A first voltage level in the context of this invention is the voltage level of a current entering a DC / DC converter circuit in the direction of electrical energy transport of that current . The current entering the DC / DC converter circuit may transport electrical energy from a three phase power network and / or another DC power source to a load or from a load to a three phase power network and / or another DC power source .

[0068] A second voltage level in the context of this invention is the voltage level of a current exiting a DC / DC converter circuit in the direction of electrical energy transport of that current . The current exiting the DC / DC converter circuit may transport electrical energy from a three phase power network and / or another DC power source to a load or from a load to a three phase power network and / or another DC power source . A first voltage level may be higher or lower than a second voltage level . Alternatively, a first voltage level may be equal to a second voltage level .

[0069] A DC / DC converter circuit can be configured to provide a constant second voltage level . The constant second voltage level can vary from a nominal second voltage level by a degree of less than or equal to 80 % or less than or equal to 60 % or less than or equal to 50 % or les s than or equal to 40 % or les s than or equal to 30 % or less than or equal to 20 % or less than or equal to 15 % or less than or equal to 10 % or less than or equal to 5 % . The voltage variations can be measured as a given number of mean voltage values of a predetermined time interval , that must l ie within a speci fied range around the nominal voltage level . For instance , for a 20 % deviation of the second voltage level from a speci fied nominal voltage level , 95 % of the 1-minute mean values of measured voltage values of an hourly interval must be within the limits of a 20 % deviation from the nominal voltage level . The time interval can be varied . The required given number of mean voltage values can be varied . Alternatively, or additionally the voltage variations can be measured according to one of the measuring principles form DIN EN 50160 , DIN EN 61000-2-2 or DIN EN 61000-2-4 or any other Norm, that suits the field of application .

[0070] A DC / DC converter circuit may comprise a plurality of switching devices connected in parallel and / or series to each other wherein the switching devices may be of the same type as the switching devices of a DC-chopper circuit .

[0071] A DC / DC converter circuit may be an integral component . In a preferred embodiment , the DC / DC converter circuit comprises a plurality of switching devices , wherein each switching device is mounted on a j oint heat sink . The DC / DC converter circuit may be configured to handle a voltage level higher than or equal to 500 VDC, particularly higher than or equal to 1000 VDC and further particularly higher than or equal to 2000 VDC .

[0072] The DC / DC converter circuit may be galvanically isolated . Particularly, the DC / DC converter circuit may comprise at least one power conducting element , wherein the power conducting element provides a galvanic isolation . The power conducting element may be an inductive element , particularly magnetic coil . Further particularly, the DC / DC converter circuit may comprise two magnetic coils . The power conducting element may be a trans former .

[0073] A DC / DC converter circuit may be a bidirectional DC / DC converter circuit . Alternatively, a DC / DC converter circuit may be a unidirectional DC / DC converter circuit .

[0074] Preferably, the power module may comprise a plurality of DC busses connected in parallel to each other, wherein one DC bus connects exactly one recti fier circuit with one DC / DC converter circuit and one inverter circuit or DC-chopper circuit . In other words , there is a one to one connection between a recti fier circuit , a DC bus , a DC / DC converter circuit and an inverter circuit or a DC-chopper circuit . Further expressed in other words , one DC bus is connected to only one recti fier circuit , only one DC / DC converter circuit and to only one inverter circuit or DC-chopper circuit .

[0075] The furnace power supply apparatus may comprise an additional power source independent of the three-phase power network . The additional power source may comprise a renewable power source like a wind turbine and / or a wind turbine power plant and / or a solar power plant and / or a geothermal power plant and / or a wave power plant and / or a battery . The additional power source may comprise a non-renewable power source like a nuclear power plant , a coal power plant , a gas-powered power plant and / or an oil- powered power plant . The additional power source may provide direct current and / or alternating current .

[0076] According to a preferred embodiment , at least one additional power source is at least indirectly, preferably directly, connectable , preferably connected, to one or more DC busses of one or more power modules of the furnace power supply apparatus . In this way, a stable energy supply for the furnace power supply apparatus can be provided even in the case of disturbances and / or failures in the three-phase power network .

[0077] The additional power source can provide , directly or indirectly, a voltage level of essentially the same voltage level as a DC bus . In this way, electrical energy can be supplied with less disturbances to the DC bus .

[0078] An additional power source may be indirectly connected to one or more DC busses o f one or more power modules via one or more DC connector circuits configured to provide a first voltage level and / or a second voltage level matching the voltage level of the additional power source and / or of the DC bus depending on the direction of electrical energy transport . In other words , in case of electrical energy flowing from the additional power source to a DC bus , the DC connector circuit can process a first voltage level of essentially the same voltage level provided by the additional power source and provide a second voltage level of essentially the voltage level of the DC bus . In case of electrical energy flowing from the DC bus to an additional power source , the DC connector circuit can process a first voltage level of essentially the same voltage level provided by the DC bus and provide a second voltage level of essentially the voltage level of the additional power source . A DC connector circuit may comprise at least one DC / DC converter circuit . An additional power source can be at least indirectly, preferably directly, connectable between the three-phase power network and a recti fier stage of the furnace power supply apparatus . In a preferred embodiment , an additional power source is connected between the three-phase power network and a recti fier stage . Particularly, an additional power source is connected between the at least one trans former and the recti fier stage . The additional power source may be connected via an AC connector circuit between the at least one trans former and the rectifier stage . The AC connector stage may be configured to provide a first voltage level and / or a second voltage level matching the voltage level provided by the one or more secondary circuits of the three-phase trans former and / or of the additional power source depending on the direction of electrical energy transport . In other words , in case of electrical energy flowing from the additional power source to a connection between the three-phase trans former and the recti fier stage , the AC connector circuit can process a first voltage level of essentially the same voltage level provided by the additional power source and provide a second voltage level of essentially the voltage level of the one or more secondary circuits of the three-phase trans former . In case of electrical energy flowing from the connection between the three-phase trans former and the recti fier stage to the additional power source , the AC connector circuit can process a first voltage level of essentially the same voltage level provided by the one or more secondary circuits of the three-phase trans former and provide a second voltage level of essentially the voltage level of the additional power source . An AC connector circuit may comprise at least one inverter circuit and / or at least one recti fier circuit .

[0079] The cooling system is configured to provide cooling power for the furnace power supply apparatus to dissipate heat losses , particularly for the one or more power modules of the furnace power supply apparatus .

[0080] The cooling system may be arranged in the power module housing . Alternatively, the cooling system may be arranged in a separate cooling system housing .

[0081] The cooling system may comprise at least one heat sink, preferably a plurality of heat sinks . A heat sink may be a pass ive heat sink or an active heat sink .

[0082] A heat sink may comprise a first cooling surface and a second cooling surface opposite to the first cooling surface . A heat sink may be a an essentially flat component . In an essentially flat component one direction of extension is signi ficantly smaller than the other two directions of extension . The first cooling surface and the second cooling surface are spaced apart to each other along the short direction of extension of the heat sink .

[0083] A passive heat sink cannot be directly temperature controlled itsel f . A passive heat sink may comprise a cooling body comprising metal and a large surface area to dissipate heat from a heat source to the environment . A passive heat sink may be a ribbed metal cooling body . A passive heat sink may also be called an air cooled heat sink .

[0084] An active heat sink can be directly temperature controlled . An active heat sink may comprise a cooling body comprising metal and one or more fluid channels , configured to transport a cooling fluid . In this way, heat from a heat source can be trans ferred via the cooling body of the active heat sink to the cooling fluid and away from the heat source with the cooling fluid . In this way, a greater amount of heat can be dissipated with an active heat sink compared to a passive heat sink . An active heat sink may also be called a fluid cooled heat sink .

[0085] An active heat sink may comprise a fluid inlet and a fluid outlet fluidly connected to the fluid inlet via the one or more fluid channels inside the cooling body .

[0086] One heat sink may be in electrical contact with at least one switching device . One heat sink may be isolated from the ground potential . In this way, the generation of parasitic current to the electrical ground connection can be prevented or at least considerably limited .

[0087] One heat sink may be arranged in direct surface contact with a switching device of a recti fier circuit and / or of an inverter circuit . Particularly, a first cooling surface of the heat sink may be in direct surface contact with the cooling surface of a switching device .

[0088] One heat sink may be arranged between two switching devices of a recti fier circuit and / or of an inverter circuit . The first surface of a first switching device housing of a first switching device may be in direct surface contact with the second cooling surface of the heat sink . The second surface of a second switching device housing of a second switching device may be in direct surface contact with the first cooling surface of the heat sink . In other words , one heat sink is sandwiched between two switching devices .

[0089] A furnace power supply apparatus designed in such a way has the advantage of a further improved cool ing capability . In the intended use of the furnace power supply apparatus , it is now possible to provide cooling power to electrical components , particularly to the switching devices , individually . In this way a locali zed cooling of the switching devices is achieved, so that heat losses can be removed with a further increased ef ficiency .

[0090] A switching device of a recti fier circuit and / or of an inverter circuit may be arranged between two heat sinks . The first surface of a first switching device housing of a first switching device may be in direct surface contact with a second cooling surface of a first heat sink . The second surface of the first switching device housing of the first switching device may be in direct surface contact with a first cooling surface of a second heat sink . In other words , one switching device is sandwiched between two heat sinks .

[0091] A furnace power supply apparatus designed in such a way has the advantage of an even further improved cooling capability . The switching devices can be cooled from two surfaces opposite to each other increasing the possible heat losses removal . Thus , the heat losses can be removed even more ef ficiently .

[0092] An integral component comprising a frame structure and stacked switching devices of a recti fier circuit and heat sinks may also be referred to as a recti fier stack .

[0093] By way of non-limiting example , a recti fier stack compri sing hori zontally stacked switching devices and heat sinks is described in the following . The rectifier stack comprises the following components in the following order : a first frame end plate , a first heat sink, a switching device , a second heat sink and a second frame end plate . The first frame end plate is in direct surface contact with the first cooling surface of the first heat sink . The second cooling surface of the first heat sink is in direct surface contact with the first surface of the switching device housing of the switching device . The second surface of the switching device housing of the switching device is in direct surface contact with the first cooling surface of the second heat sink . The second cooling surface of the second heat sink is in direct surface contact with the second frame end plate . The first frame end plate and the second frame end plate are mechanically connected via four connection elements , preferably connection rods , to each other and apply a compressive force on the stacked heat sinks and the switching device housing .

[0094] An integral component comprising a frame structure and stacked switching devices of an inverter circuit and heat sinks may also be referred to as an inverter stack .

[0095] By way of non-limiting example , an inverter stack compri sing vertically stacked switching devices and heat sinks is described in the following . The inverter stack comprises the following components in the following order : a first frame end plate , a first heat sink, a first switching device , a second heat sink, a second switching device , a third heat sink and a second frame end plate . The first frame end plate is in direct surface contact with the first cool ing surface of the first heat sink . The second cooling surface of the first heat sink is in direct surface contact with the first surface of the switching device housing of the first switching device . The second surface of the switching device housing of the first switching device is in direct surface contact with the first cooling surface of the second heat sink . The second cooling surface of the second heat sink i s in direct surface contact with the first surface of the switching device housing of the second switching device . The second surface of the switching device housing of the second switching device is in direct surface contact with the first cooling surface of the third heat sink . The second cooling surface of the third heat sink is in direct surface contact with the second frame end plate . The first frame end plate and the second frame end plate are mechanically connected via four connection elements , preferably connection rods , to each other and apply a compressive force on the stacked heat sinks and the switching device housings .

[0096] By way of non-limiting example , an embodiment of a DC-Chopper circuit comprising a plurality of switching devices , wherein the switching devices are mounted on a j oint heat sink is described in the following . The DC-Chopper circuit comprises a heat sink and a plurality of switching devices , wherein each switching device comprises a separate switching device housing . The switching device housings of the switching devices are mounted on the same surface of the heat sink . The switching device housings are arranged in a matrix structure , that is they are arranged in rows and columns on the heat sink . The cool ing surfaces of the switching device housings are in direct surface contact with the cooling surface of the heat sink . The switching devices are electrically isolated from the heat sink .

[0097] The furnace power supply apparatus may comprise an electronic control unit . An electronic control unit is any electronic system, which is adapted to receive signals and / or to store signals and / or to process signals and / or to control or regulate a furnace power supply apparatus in dependence on at least one signal .

[0098] The furnace power supply apparatus can include one or more sensors to provide information about harmonic distortions and / or flicker and / or a ratio of active power flow and reactive power flow in the power network . The electronic control unit can be operatively connected to one or more such sensors and can receive sensor signals , process them, and use them to control and / or regulate the furnace power supply apparatus . An electronic control unit can be adapted to control and / or regulate a recti fier stage , particular a recti fier circuit , in particular to reduce or prevent harmonic distortions and / or flicker, in particular to mitigate flicker, in the power network . An electronic control unit can be adapted to control and / or regulate a converter stage , particularly an inverter circuit or a DC-chopper circuit , in particular to reduce or prevent harmonic distortions and / or flicker, in particular to mitigate flicker, in the power network and / or to optimi ze the ratio of active power flow and reactive power flow in the power network .

[0099] An electronic control unit can be adapted to control and / or regulate a DC-chopper circuit or an inverter circuit , in particular to reduce or prevent harmonic distortions and / or flicker, in particular to mitigate flicker, in the power network, in particular preferably by applying a pulse-width modulation strategy algorithm .

[0100] Preferably, the cooling system comprises a first cooling circuit configured to guide a cooling fluid to and away from the power module .

[0101] The first cooling circuit may comprise at least one component supply line and at least one component drain line fluidly connected to the at least one component supply line forming a component cooling circuit . The component supply line may be connected to a fluid inlet of an active heat sink and the component drain line may be connected to a fluid outlet of the active heat sink, thereby fluidly connecting the component supply line with the component drain line via the fluid channel of the active heat sink .

[0102] A furnace power supply apparatus designed in such a way has the advantage of a further improved cool ing capability . In the intended use of the furnace power supply apparatus , it is now possible to provide cooling power to electrical components , particularly to switching devices , individually . In this way, heat losses can be removed with a further increased ef ficiency . The component supply line and the component drain line may be fluidly connected via a fluid pipe . The fluid pipe may comprise at least one winding . Preferably, the fluid pipe comprises a spiral form comprising a plurality of windings . The fluid pipe may limit a component accommodation volume at least partially . The component accommodation volume may be configured to accommodate a switching device , preferably a switching device comprising a cylindrical switching device housing .

[0103] A furnace power supply apparatus designed in such a way has the advantage of a further improved cool ing capability . In the intended use of the furnace power supply apparatus , it is now possible to provide cooling power to electrical components , particularly to switching devices , individually . In this way, heat losses can be removed with a further increased ef ficiency .

[0104] The first cooling circuit may comprise a stack supply line and a stack drain line fluidly connected to the stack supply line forming a stack cooling circuit .

[0105] The component supply line may be fluidly connected to the stack supply line and the component drain line may be fluidly connected to the stack drain line . In other words , the stack supply line and the stack drain line may be fluidly connected via the component cooling circuit formed by the component supply line and the component drain line .

[0106] The first cooling circuit may comprise a first main supply line and a first main drain line fluidly connected to the first main supply line .

[0107] The stack supply line may be fluidly connected to the first main supply line and the stack drain line may be fluidly connected to the first main drain line . In other words , the first main supply line and the first main drain line may be fluidly connected via the stack cooling circuit formed by the stack supply line and the stack drain line .

[0108] The first main supply line and the first main drain line may be arranged outside the power module housing, preferably under the power module housing . In this way, each stack cooling circuit can be provided with the same cooling fluid temperature at the stack supply line . In this way, heat losses can be removed with an increase accuracy .

[0109] The power module housing may comprise at least one stack cooling circuit inlet , preferably arranged in the bottom part of the power module housing and at least one stack cooling circuit outlet , preferably arranged in the bottom part of the power module housing .

[0110] The stack cooling circuit may be partially arranged in the power module housing . Particularly, the stack supply line may start outside the power module hous ing and enter the power module housing . Preferably, the stack supply line may enter the power module housing through the stack cool ing circuit inlet . The stack drain line may start inside the power module housing and exit the power module housing . Preferably, the stack drain line may exit the power module housing through the stack cooling circuit outlet . In such a stack cool ing circuit , cooling fluid flowing in the main supply line can enter the stack supply line outside the power module housing, flowing through part of the stack cooling circuit inside the power module housing and exit the power module housing through the stack drain line . From the stack drain line , the cooling fluid can enter the main drain line .

[0111] The component cooling circuit may be arranged in the power module housing . Preferably, the first main supply line and the first main drain line are arranged hori zontally . The stack supply line and the stack drain line are preferably arranged vertically . The component supply line and the component drain line are preferably arranged hori zontally .

[0112] Alternatively, the main supply line and the main drain line are arranged vertically . The stack supply line and the stack drain line are preferably arranged hori zontally . The component supply line and the component drain line are preferably arranged vertically or hori zontally .

[0113] Arranged hori zontally in this context means , that a flow direction of a cooling fluid is essentially hori zontal . Arranged vertically in this context means , that a flow direction of a cooling fluid is essentially vertically .

[0114] The main supply line and the main drain line may comprise or consist of metal material . The stack supply line , the stack drain line , the component supply line and the component drain line may comprise or consist of plastic material .

[0115] A furnace power supply apparatus designed in such a way, has the advantage of an increased protection from electrical failure due to fluid leakage in the cooling circuit . In case the cooling circuit has a leak, cooling fluid might potentially get in contact with electrical components under electrical voltage resulting in unwanted electrical currents and / or electrical voltages within the cooling circuit . By designing parts of the cooling circuit from plastic material , the electrical conductivity i s signi ficantly reduced, resulting in a higher protection against unwanted electrical currents and electrical voltages in the cooling circuit . The main supply line and the main drain line may each comprise a bigger diameter than the stack supply line , the stack drain line , the component supply line and the component drain line . The stack supply line and the stack drain line may each comprise a bigger diameter than the component supply line and the component drain line .

[0116] The cooling system may comprise a plurality of stack cooling circuits . Particularly, the cooling system may comprise one stack cooling circuit for each recti fier stack and one stack cooling circuit for each inverter stack of the power module . The plurality of stack cooling circuits may be fluidly connected to the same main drain line and main supply line .

[0117] The cooling system may comprise a plurality of component cooling circuits . Particularly, the cooling system may comprise at least one component cooling circuit for each active heat sink of the power module . The component supply lines and the component drain lines connected to active heat sinks of one recti fier stack or one inverter stack may be fluidly connected to the same stack cooling circuit of the respective recti fier stack or inverter stack .

[0118] In the intended use of the furnace power supply apparatus , it i s now possible to provide cooling power to electrical components , particularly to switching devices , individually . In thi s way, heat losses can be removed with a further increased ef ficiency .

[0119] The cooling fluid may comprise or be water, preferably de-ioni zed water, further preferred de-ionized water with an electrical conductivity within a range of h 1 pS / cm and < 50 pS / cm, preferably within a range of > 0 , 5 pS / cm and < 1 pS / cm and preferred within a range of > 0 , 1 pS / cm and < 0 , 5 pS / cm . Particularly preferred, the electrical conductivity of the de-ioni zed water may be within a range of > 0 , 055 pS / cm and < 0 , 1 pS / cm . A furnace power supply apparatus designed in this way has the advantage of an increased protection against unwanted electrical currents and / or electrical voltages in the cooling circuit .

[0120] A cooling circuit may comprise a heat exchanging element to remove heat from the cooling fluid, particularly the de-ioni zed water . In this way, the de-ioni zed water circuit can be separated from a raw water circuit .

[0121] The heat exchanging element may be a plate heat exchanger .

[0122] The furnace power supply apparatus may comprise a separate cooling system for each power module . Alternatively, the furnace power supply apparatus may comprise one cooling system for a plurality of power modules . The cooling system may comprise a plurality of cooling circuits , preferably one separate cool ing circuit for each power module . In other words , the number of cooling circuits and the number of power modules may be the same .

[0123] The first cooling circuit may comprise a plurality of valves , particularly between the first and / or second cooling fluid pump and the first main supply line and the first main drain line . Further, one or more valves may be arranged between the first main supply line and the stack supply line . Further, one or more valves may be arranged between the first main drain line and the stack drain line . Further, one or more valves may be arranged between the stack supply line and the component supply line . Further, one or more valves may be arranged between the stack drain line and the component drain line . The valve and / or the valves can be moved between an open position and a close position .

[0124] In this way, the first cooling circuit can by interrupted in order to shorten maintenance time and / or in order to exchange single parts of the power module like the recti fier stage , the converter stage , a recti fier stack and / or an inverter stack .

[0125] Preferably, the cooling system comprises a first cooling fluid pump configured to transport the cooling fluid through the first cooling circuit .

[0126] The cooling system may comprise a second cooling fluid pump . The second cooling fluid pump may be a reserve cooling fluid pump, configured to automatically turn on, in case the first cooling fluid pump has a defect and / or mal function . The first cooling fluid pump and the second cool ing fluid pump may be the same type of cooling fluid pump .

[0127] The cooling fluid pump may be arranged in the cooling system housing . The cooling fluid pump may be a flow pump, particularly an axial- flow pump, a radial- flow pump or a combination of an axial- flow pump and a radial- flow pump . The cooling fluid pump may be a positive displacement pump, particularly a piston pump, particularly a rotary piston pump or an axial piston pump, a membrane pump, a screw conveyer based pump or an impeller based pump .

[0128] The cooling fluid pump may be configured to transport a cooling fluid through the first cooling circuit and / or the second cooling circuit at a rate of > 100 1 / min, preferably > 250 1 / min, preferred > 500 1 / min and particularly preferred > 1000 1 / min .

[0129] Preferably, the cooling system comprises a filtration system preferably a de-ioni zing system, configured to regulate and / or control the electrical conductivity of the cooling fluid .

[0130] The filtration system may be configured to regulate and / or control the electrical conductivity of the cooling fluid to an electrical conductivity within a range of h 1 pS / cm and < 50 pS / cm, preferably within a range of > 0 , 5 pS / cm and

[0131] < 1 pS / cm and preferred within a range of > 0 , 1 pS / cm and

[0132] < 0 , 5 pS / cm . Particularly preferred, the filtration system may be configured to regulate and / or control the electrical conductivity of the cooling fluid to an electrical conductivity within a range of > 0 , 055 pS / cm and < 0 , 1 pS / cm .

[0133] A furnace power supply apparatus designed in this way has the advantage of an increased protection against unwanted electrical currents and / or electrical voltages in the cooling circuit .

[0134] Preferably, the cooling system comprises at least one air conditioning system .

[0135] The air conditioning system may be configured to supply cooling power to the power module . Particularly, the air conditioning system may be configured to drain heat and humidity from air of the power module housing volume .

[0136] The air conditioning system may comprise at least one main air supply duct . The main air supply duct may be arranged outside the power module housing, preferably under the power module housing . The main air supply duct may be arranged hori zontally .

[0137] The air conditioning system may comprise at least one , pre ferably a plurality of , air supply duct / ducts . The air supply duct may be fluidly connected to the main air supply duct . The air supply duct may be arranged vertically . The air supply duct may be arranged outside the power module housing, preferably under the power module housing .

[0138] The power module housing may comprise at least one air supply inlet , preferably arranged in the bottom part of the power module housing . The air supply duct may be fluidly connected to the power module housing volume via the air supply inlet . The power module housing may comprise at least one air drain outlet , preferably a plurality of air drain outlets . The air drain outlet is preferably arranged in the top part or in a side part of the power module housing .

[0139] The air conditioning system may comprise at least one heat exchanging element , configured to remove heat and humidity from air of the power module housing to the environment .

[0140] The heat exchanging element may be arranged in the cooling system housing . Alternatively, the heat exchanging element may be arranged in the power module housing, particularly in the top part of the power module hous ing or in a side part of the power module housing .

[0141] The cooling system may be configured to provide cooling power through the first cooling circuit and the air conditioning system to the power module . The cool ing power can be provided in such a way, that one part of the cool ing power is provided by the first cooling circuit and the respective other part is provided by the air conditioning system . Particularly, the part of cooling power provided by the first cool ing circuit can be 1 70 % of the total cooling power and the part of cooling power provided by the air conditioning system can by < 30 % of the total cooling power . The part of cooling power provided by the first cooling circuit can be 1 80 % of the total cooling power and the part of cooling power provided by the air conditioning system can by < 20 % of the total cooling power . According to a preferred embodiment , the part of cooling power provided by the first cooling circuit can be 1 90 % of the total cooling power and the part of cooling power provided by the air conditioning system can by < 10 % of the total cooling power . The total cooling power is the amount of cooling power provided by the cooling system to the power module at any given time .

[0142] Preferably, the cooling system comprises a temperature and humidity control unit configured to regulate and / or control the temperature of the power module and / or the humidity of a power module housing volume .

[0143] A temperature and humidity control unit is any electronic system, which is adapted to receive signals and / or to store signal s and / or to process signals and / or to control and / or regulate the temperature of the power module and / or the humidity of the power module housing volume of the furnace power supply apparatus in dependence on at least one signal .

[0144] The furnace power supply apparatus can include one or more sensors to provide information about the temperature of the power module and / or the humidity of the power module housing volume . The temperature and humidity control unit can be operatively connected to one or more such sensors and can receive sensor signals , process them, and use them to control and / or regulate the temperature of the power module and / or the humidity of the power module housing volume . The temperature and humidity control unit may be operatively connected to the cooling system, particularly to the cooling fluid pump and the air conditioning system .

[0145] The sensors may be temperature and / or humidity sensors . The sensors may be arranged at the recti f ier stage , at the DC bus , at the converter stage and / or inside the power module housing .

[0146] The temperature and humidity control unit can be adapted to regulate and / or control the temperature of the recti fier stage , the DC bus and / or the converter stage individually . Particularly, the temperature and humidity control unit can be adapted to regulate and / or control the temperature and / or the humidity of the power module housing volume .

[0147] The temperature and humidity control unit can be adapted to regulate and / or control the temperature of the recti fier stage , the DC bus and / or the converter stage and / or the temperature and humidity of the power module housing volume in dependence of the control and / or regulation of the electronic control unit . In case a high amount of electrical energy during the intended use of the furnace power supply apparatus is required, for instance at the beginning of and during a melting process in an electric furnace , a higher amount of cooling power is required . The temperature and humidity control unit is thus configured to receive sensor signals , process them, and use them to control and / or regulate the cooling system to provide a high amount of cooling power to the power module housing volume , the recti fier stage , the DC bus and / or the converter stage , particularly by increasing the cooling fluid volume flow of the at least one first cooling circuit and / or by increasing the air volume flow of the air conditioning system .

[0148] Preferably, the furnace power supply apparatus comprises a power module housing, wherein the power module housing limits a power module housing volume at least partially and the power module is arranged in the power module housing volume .

[0149] Preferably, the power module housing limits the amount of emissions from electromagnetic fields .

[0150] Preferably, the power module housing comprises electrically conductive material , particularly metal . In this way, the housing may reduce the amount of emiss ions caused from of electromagnetic fields by high currents running through the electrical components inside the housing . Thus , the exposure of people to electromagnetic fields is reduced . Preferably, the power module hous ing comprises an electromagnetic shielding . Further preferred, the electromagnetic shielding may comprise a or consist of a metal mesh . The metal mesh may be arranged in the power module housing volume . In this way, the amount of emissions from electromagnetic fields by high currents running through the electrical component inside the housing is even further reduced .

[0151] Alternatively or in addition, the power module housing may be designed as an electromagnetic shielding .

[0152] Preferably, the housing is connected to a ground potential .

[0153] Preferably, the furnace power supply apparatus comprises at least one three-phase trans former, wherein the three-phase trans former comprises a primary circuit per phase and one or more secondary circuits per phase .

[0154] The primary circuit of the three-phase trans former may be connectable to a three-phase power network . The one or more secondary circuits may be connected to the at least one power module of the furnace power supply apparatus , preferably to the rectifier stage and further preferred to the at least one three-phase recti fier circuit of the furnace power supply apparatus .

[0155] The one or more secondary circuits per phase of the three-phase trans former may be connected to exactly one power module . In other words , the one or more secondary circuits per phase of the three-phase trans former may be connected to the same power module . Preferably, the furnace power supply apparatus comprises a plurality of three-phase trans formers , wherein each trans former is connected to exactly one power module . In other words , there is a one to one connection between a three-phase trans former and a power module . Preferably, the three-phase trans former is a phase-shi fting trans former .

[0156] A phase-shi fting trans former is a speciali zed type of transformer, which can be configured to adj ust the phase relationship between its primary circuits and its secondary circuits . A furnace power supply apparatus designed in such a way has the advantage of being able to control , preferably to minimi ze , undesirable electrical network distortions caused by the electric furnace operation, without the need for an active front end .

[0157] Preferably, the three-phase trans former is a dry-type transformer .

[0158] A dry-type trans former is a trans former, that does neither use a liquid as a cooling medium nor as an insulating medium for the its windings and core . Instead a dry-type trans former uses a gaseous fluid, preferably air, as cooling medium and a solid material , preferably an epoxy resin, polyester resin and / or aramid material , as an insulating medium . A furnace power supply apparatus designed in such a way has the advantage of facilitating initial installation as wel l as a reduction fire potential during failure due to cooling medium inflammation .

[0159] Preferably, the furnace power supply apparatus comprises a disconnector, wherein the disconnector is arranged between the converter stage and the electric furnace .

[0160] The disconnector is configured to interrupt an electrical connection between the converter stage and the electric furnace .

[0161] The furnace power supply apparatus may comprise one or more disconnectors arranged between the three-phase power network and the electric furnace , particularly between the three-phase power network and the rectifier stage , between the recti fier stage and the converter stage , between the rectifier stage and the DC bus , between the DC bus and the converter stage and / or between the converter stage and the electric furnace .

[0162] The disconnectors may be configured to connect the trans former primary with the ground potential , when the disconnectors are in an open position .

[0163] Preferably, the recti fier stage of a power module comprises at least one three-phase recti fier circuit , and at least one three-phase recti fier circuit per power module is connected to the DC bus .

[0164] Preferably, the furnace power supply apparatus comprises a plurality of power modules connected in parallel to each other .

[0165] Preferably, at least one three-phase recti fier circuit of a recti fier stage of a first power module and at least one three-phase recti fier circuit of a recti fier stage of a second power module are connected to the same DC bus .

[0166] Preferably, the furnace power supply apparatus comprises a rec- ti f ier-stage-disconnector, wherein the recti f ier-stage-discon- nector is arranged between the recti fier stage and the DC bus .

[0167] Preferably, recti fier-stage-disconnector is arranged between at least one three-phase recti fier and the DC bus that the at least one three-phase recti fier is connected to .

[0168] Preferably, furnace power supply apparatus comprises an in- verter-stage-disconnector , wherein the inverter-stage-discon- nector is arranged between the inverter stage and the DC bus . Preferably, the converter stage comprises at least one multi-phase inverter circuit , preferably a three-phase inverter circuit , configured to power at least two di f ferent phases of the electric furnace .

[0169] Preferably, the furnace power supply apparatus comprises at least two power modules wherein a first converter stage of a first power module and a second converter stage of a second power module are connected to the same DC bus .

[0170] Preferably, the furnace power supply apparatus comprises at least two power modules , wherein the converter stages of each power module comprise at least two single-phase inverter circuits , wherein each single-phase inverter circuit is configured to power a di f ferent phase of the electric furnace , and wherein the single-phase inverter circuits configured to power the same phase of the electric furnace are connected to the same DC bus .

[0171] Preferably the furnace power supply apparatus comprises at least two DC busses , wherein the single phase inverter circuits configured to power a first phase of the electric furnace are connected to a first DC bus , and wherein the single phase inverter circuits configured to power a second phase of the electric furnace are connected to a second DC bus .

[0172] Preferably, the ratio of the number of inverter circuits to the number of three-phase recti fier circuits within one power module is two or more .

[0173] Preferably, the single-phase inverter circuits of an inverter stage of a power module are connected with a star connection to each other .

[0174] Preferably, star centers of the individual inverter stages o f the power modules are connected to each other to a neutral (N) . Preferably, single-phase inverter circuits or the three-phase inverter circuits of an inverter stage of a power module are connected with a delta connection to each other .

[0175] The problem underlying the invention is further solved by an electric furnace comprising at least one furnace power supply apparatus according the above description .

[0176] The problem underlying the invention is further solved by a production line for proces sing metal workpieces comprising at least one furnace power supply apparatus according to the above description and at least one metal workpiece processing apparatus .

[0177] The metal workpiece processing apparatus may be a rolling machine , a punching machine , press hardening machine or any other machine suitable to process metal workpieces .

[0178] Further advantages , details and features of the present invention are explained in the description of the following embodiments , thereby :

[0179] Figure 1 : shows a schematic view of a first embodiment of a furnace power supply apparatus ;

[0180] Figure 2 : shows a schematic view of a second embodiment of a furnace power supply apparatus , and

[0181] Figure 3 : shows a schematic view of an inverter stack of a furnace power supply apparatus according to a third embodiment . In the following description, same reference numerals describe same elements and same features , respectively, so that a description of one element conducted with reference to one figure is also valid for the other figures , so that repetition of the respective feature is omitted .

[0182] Fig . 1 shows a furnace power supply apparatus 20 for the supply of an electric furnace with electric energy according to a first embodiment . The furnace power supply apparatus 20 is connected to a three-phase power network 10 and one electrode 30 of the electric furnace . The furnace power supply apparatus 20 comprises one power module 100 , wherein the power module 100 comprises a recti fier stage 110 , connected to the three-phase power network 10 , and a converter stage 120 , connected to the electrode 30 of the electric furnace . The furnace power supply apparatus 20 comprises one DC bus 130 , wherein the DC bus 130 connects the recti fier stage 110 to the converter stage 120 of the power module 100 . The furnace power supply apparatus 20 comprises a cooling system 140 .

[0183] Fig . 2 shows furnace power supply apparatus 20 according to a second embodiment . The furnace power supply apparatus 20 comprises a power module housing 101 , wherein the power module housing 101 limits a power module housing volume 102 partial ly and the power module 100 is arranged in the power module housing volume 102 .

[0184] The power module 100 comprises a recti fier stage 110 , a converter stage 120 and a DC bus 130 , wherein the DC bus 130 connects the recti fier stage to the converter stage 120 .

[0185] The furnace power supply apparatus 20 further comprises a cooling system 140 , wherein the cooling system 140 is arranged in a separate cooling system housing 141 . The cooling system 140 comprises a first cooling circuit 150 configured to guide a cooling fluid to and away from the power module 100 .

[0186] The first cooling circuit 150 comprises a plurality of component cooling circuits 170 , wherein each component cooling circuit 170 comprises a component supply line 171 and a component drain line 172 , wherein the component supply line 171 is fluidly connected to the component drain line 172 forming the component cooling circuit 170 . The component cooling circuits 170 are arranged in the power module housing 101 .

[0187] The first cooling circuit 150 comprises two stack cooling circuits 160 , wherein each stack cooling circuit 160 comprises a stack supply line 161 and a stack drain line 162 , wherein the stack supply line 161 is fluidly connected to the stack drain line 162 forming the stack cooling circuit 160 .

[0188] A plurality of component supply lines 171 is fluidly connected to the stack supply lines 161 and a plurality of component drain lines 172 is fluidly connected to the stack drain line 162 . In other words , the stack supply line 161 and the stack drain 162 are fluidly connected via the component cooling circuits 170 formed by the component supply lines 171 and the component drain lines 172 .

[0189] The first cooling circuit 150 comprises a first main supply line 151 and a first main drain line 152 fluidly connected to the first main supply line 151 .

[0190] The stack supply lines 161 are fluidly connected to the first main supply line 151 and the stack drain lines 162 are fluidly connected to the first main drain line 152 . In other words , the first main supply line 151 and the first main drain line 152 are fluidly connected via the stack cool ing circuits 160 formed by the stack supply lines 161 and the stack drain lines 162 .

[0191] The first main supply line 151 and the first main drain line 152 are arranged outside the power module housing 101 under the power module housing 101 .

[0192] The power module housing 101 comprises two stack cooling circuit inlets 163 arranged in the bottom part 103 of the power module housing 101 and two stack cool ing circuit outlets 164 arranged in the bottom part 103 of the power module housing 101 . The stack supply lines 161 start outside the power module housing 101 and enter the power module housing 101 through the stack cooling circuit inlets 163 . The stack drain lines 162 start inside the power module housing 101 and exit the power module housing 101 through the stack cooling circuit outlets 164 .

[0193] The power module housing 101 is designed as an electromagnetic shielding 105 . The power module housing 101 is electrically connected to the electrical ground 106 .

[0194] The first main supply line 151 and the first main drain line 152 are arranged hori zontally . The stack supply lines 161 and the stack drain lines 162 are arranged vertically . The component supply lines 171 and the component drain lines 172 are arranged hori zontally .

[0195] The cooling system 140 comprises a first cooling fluid pump 153 configured to transport the cooling fluid through the first cooling circuit 150 . The first cooling fluid pump 153 is fluidly connected to the first main supply line 151 and the first main drain line 152 via a filtrations system 154 . The filtration system is configured to regulate and / or control the electrical conductivity of the cooling fluid to an electrical conductivity within a range of h 1 pS / cm and < 50 pS / cm . The cooling system 140 further comprises an air conditioning system 180 . The air conditioning system 180 is configured to supply cooling power to the power module 100 . The air conditioning system 180 is configured to drain heat from air of the power module housing volume 102 .

[0196] The air conditioning system 180 comprises one main air supply duct 181 . The main air supply duct 181 is arranged outside the power module housing 101 . The main air supply duct 181 is arranged under the power module housing 101 . The main air supply duct 181 is arranged hori zontally .

[0197] The air conditioning system 180 comprises two air supply ducts 183 . The air supply ducts 183 are fluidly connected to the main air supply duct 181 . The air supply ducts 183 are arranged vertically . The air supply ducts 183 are arranged outside and under the power module housing 101 .

[0198] The power module housing 101 comprises at least one air supply inlet 184 arranged in the bottom part 103 of the power module housing 101 . The air supply duct 183 is fluidly connected to the power module housing volume 102 via the air supply inlet 184 .

[0199] The power module housing 101 comprises one air drain outlet 185 . The air drain outlet 185 i s arranged in a s ide part 104 o f the power module housing 101 .

[0200] The air conditioning system 180 comprises one heat exchanging element 186 , configured to remove heat from air of the power module housing 101 to the environment . The heat exchanging element 186 is arranged in the cooling system housing 141 .

[0201] A main air drain duct 182 fluidly connects the heat exchanging element 186 with the power module housing volume 102 . The main air drain duct 182 i s connected to the air drain outlet 185 of the power module housing 101 .

[0202] Figure 3 shows an inverter stack 200 of a furnace power supply apparatus 20 according to a third embodiment . The inverter stack 200 comprises a first frame end plate 410 , a first heat sink 250 , a first switching device 210 , a second heat sink 260 , a second switching device 230 , a third heat sink 270 and a second frame end plate 420 . The first frame end plate 410 is in direct surface contact with the first cooling surface 251 of the first heat sink 250 . The second cooling surface 252 of the first heat sink 250 is in direct surface contact with the first surface 221 of the first switching device housing 220 of the first switching device 210 . The second surface 222 of the first switching device housing 220 of the first switching device 210 is in direct surface contact with the first cooling surface 261 of the second heat sink 260 . The second cooling surface 262 of the second heat sink 260 is in direct surface contact with the first surface 241 of the second switching device housing 240 of the second switching device 230 . The second surface 242 of the second switching device housing 240 of the second switching device 230 is in direct surface contact with the first cooling surface 271 of the third heat sink 270 . The second cool ing surface 272 of the third heat sink is in direct surface contact with the second frame end plate 420 . The first frame end plate 410 and the second frame end plate 420 are mechanically connected via four connection elements 430 to each other and apply a compressive force on the stacked heat sinks 250 , 260 , 270 and the switching device housings 220 , 240 . The heat sinks 250 , 260 , 270 and the switching devices 210 , 230 are stacked vertically . The first frame end plate 410 , the second frame end plate 420 and the connection elements 430 form a frame structure 400 . The inverter stack 200 comprises three component cool ing circuits 170 . Each component cooling circuit 170 comprises one component supply line 171 and one component drain line 172 . Each o f the component supply lines 171 is connected to a fluid inlet of an active heat sink 250 , 260 , 270 and each of the component drain lines 172 is connected to a fluid outlet of the active heat sink 250 , 260 , 270 , thereby fluidly connecting the respectively one component supply line 171 with one component drain line 172 via the fluid channel of the active heat sink 250 , 260 , 270 .

[0203] The component supply lines 171 are fluidly connected to the stack supply line 161 and the component drain lines 172 are fluidly connected to the stack drain line 162 . In other words , the stack supply line 161 and the stack drain line 162 are fluidly connected via the component cool ing circuits 170 formed by the component supply lines 171 and the component drain lines 172 .

[0204] List of reference numerals

[0205] 10 Three-phase power network

[0206] 20 Furnace power supply apparatus

[0207] 30 Electrode ( of an electric furnace )

[0208] 100 Power module

[0209] 101 Power module housing

[0210] 102 Power module housing volume

[0211] 103 Bottom part ( of the power module housing)

[0212] 104 Side part ( of the power module housing)

[0213] 105 Electromagnetic shielding

[0214] 106 Electrical ground

[0215] 110 Recti fier stage

[0216] 120 Converter stage

[0217] 130 DC bus

[0218] 140 Cooling system

[0219] 141 Cooling system housing

[0220] 150 First cooling circuit

[0221] 151 First main supply line

[0222] 152 First main drain line

[0223] 153 Cooling fluid pump

[0224] 154 Filtration system

[0225] 160 Stack cooling circuit

[0226] 161 Stack supply line

[0227] 162 Stack drain line

[0228] 163 Stack cooling circuit inlet

[0229] 164 Stack cooling circuit outlet

[0230] 170 Component cooling circuit

[0231] 171 Component supply line

[0232] 172 Component drain line

[0233] 180 Air conditioning system

[0234] 181 Main air supply duct

[0235] 182 Main air drain duct

[0236] 183 Air supply duct

[0237] 184 Air supply inlet Air drain outlet

[0238] Heat exchanging element

[0239] Inverter stack

[0240] First switching device ( of an inverter circuit )

[0241] First switching device housing ( of the first switching device )

[0242] First surface ( of the first switching device housing)

[0243] Second surface ( of the first switching device housing)

[0244] Second switching device ( of an inverter circuit )

[0245] Second switching device housing ( of the second switching device )

[0246] First surface ( of the second switching device housing)

[0247] Second surface ( of the second switching device housing)

[0248] First heat sink

[0249] First cooling surface ( of the first heat sink)

[0250] Second cooling surface ( of the first heat sink)

[0251] Second heat sink

[0252] First cooling surface ( of the second heat sink)

[0253] Second cooling surface ( of the second heat sink)

[0254] Third heat sink

[0255] First cooling surface ( of the third heat sink)

[0256] Second cooling surface ( of the third heat sink)

[0257] Frame structure

[0258] First frame end plate

[0259] Second frame end plate

[0260] Connection element

Claims

Claims1. Furnace power supply apparatus (20) for the supply of an electric furnace with electric energy, wherein the furnace power supply apparatus (20) is connectable to a three-phase power network (10) and at least one electrode (30) of the electric furnace; wherein the furnace power supply apparatus (20) comprises at least one power module (100) , wherein the power module (100) comprises: a rectifier stage (110) , connectable to a three-phase power network (10) , and a converter stage (120) , connectable to at least one electrode (30) of the electric furnace; wherein the furnace power supply apparatus (20) comprises at least one DC bus (130) , wherein the DC bus (130) connects the rectifier stage (110) to the converter stage (120) of the at least one power module (100) , wherein the furnace power supply apparatus (20) is characterized in that the furnace power supply apparatus (20) comprises a cooling system (140) .

2. Furnace power supply apparatus (20) according to claim 1, characterized in that the cooling system (140) comprises a first cooling circuit (150) configured to guide a cooling fluid to and away from the power module (100) .

3. Furnace power supply apparatus (20) according to claim 2, characterized in that the cooling system (140) comprises a first cooling fluid pump (153) configured to transport the cooling fluid through the first cooling circuit (150) .

4. Furnace power supply apparatus (20) according to one of the claims 2 to 3, characterized in that cooling system (140) com-prises a filtration system (154) , preferably a de-ionizing system, configured to regulate and / or control the electrical conductivity of the cooling fluid.

5. Furnace power supply apparatus (20) according to one of the preceding claims, characterized in that the cooling system (140) comprises at least one air conditioning system (180) .

6. Furnace power supply apparatus (20) according to one of the preceding claims, characterized in that the cooling system (140) comprises a temperature and humidity control unit configured to regulate and / or control the temperature of the power module (100) and / or the humidity of a power module housing volume (102) .

7. Furnace power supply apparatus (20) according to one of the preceding claims, characterized in that the furnace power supply apparatus (20) comprises a power module housing (101) , wherein the power module housing limits a power module housing volume (102) at least partially and the power module (100) is arranged in the power module housing volume (102) .

8. Furnace power supply apparatus (20) according to claim 7, characterized in that the power module housing (101) limits the amount of emissions from electromagnetic fields.

9. Furnace power supply apparatus (20) according to one of the preceding claims, characterized in that the furnace power supply apparatus (20) comprises at least one three-phase transformer, wherein the three-phase transformer comprises a primary circuit per phase and one or more secondary circuits per phase.

10. Furnace power supply apparatus (20) according to one of the preceding claims, characterized in that the furnace power supplyapparatus (20) comprises a disconnector, wherein the disconnector is arranged between the converter stage (120) and the electric furnace.

11. Furnace power supply apparatus (20) according to one of the preceding claims, characterized in that: the rectifier stage (110) of a power module (100) comprises at least one three-phase rectifier circuit, and at least one three-phase rectifier circuit per power module (100) is connected to the DC bus (130) .

12. Furnace power supply apparatus (20) according to one of the preceding claims, characterized in that the furnace power supply apparatus (20) comprises a plurality of power modules (100) connected in parallel to each other.

13. Furnace power supply apparatus (20) according to one of the preceding claims, characterized in that the furnace power supply apparatus (20) comprises at least two power modules (100) , and wherein the converter stages (120) of each power module (100) comprise at least two single-phase inverters, wherein each single-phase inverter is configured to power a different phase of the electric furnace, and wherein the single-phase inverters configured to power the same phase of the electric furnace are connected to the same DC-bus (130) .

14. Furnace power supply apparatus (20) according to claim 13, characterized in that: the furnace power supply apparatus (20) comprises at least two DC-busses () , wherein the single-phase inverters configured to power a first phase of the electric furnace are connected to a first DC-bus (130) , andwherein the single-phase inverters configured to power a second phase of the electric furnace are connected to a second DC-bus (130) .

15. Electric furnace comprising at least one furnace power supply apparatus (20) according to one the preceding claims.

16. Production line for processing metal workpieces comprising at least one furnace power supply apparatus (20) according to one of the claims 1 to 14 and at least one metal workpiece processing apparatus.

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