Patent ID: 12244150

To facilitate comprehension, the same reference numbers have been used, where possible, to identify identical common elements in the drawings. It is understood that elements and characteristics of one embodiment can conveniently be incorporated into other embodiments without further clarifications.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

We will now refer in detail to the possible embodiments of the invention, of which one or more examples are shown in the attached drawings. Each example is supplied by way of illustration of the invention and shall not be understood as a limitation thereof. For example, one or more characteristics shown or described insomuch as they are part of one embodiment can be varied or adopted on, or in association with, other embodiments to produce another embodiment. It is understood that the present invention shall include all such modifications and variants.

With reference to the attached drawings, see for exampleFIG.1, an electric power supply apparatus10a, for a user device12, for example an electric arc furnace for steel industry applications, or for the glass or metal processing sector, according to the present invention comprises means for connection to an electricity grid11and at least one electric line13for the connection of the electricity grid11to the electric arc furnace12, wherein the electric line13comprises one or more electric apparatuses located between the electricity grid11and the electric arc furnace12.

The electric line13can be provided with means for connection to the electricity grid11and to the user device12.

According to some embodiments, the user device12can be an electric arc furnace of the type powered with alternating current12AC.

The electricity grid11can be, for example, an electricity grid which supplies high voltage electrical energy, in particular in alternating current, having predefined mains voltage, current and frequency values.

The user device12could also be, instead of an electric arc furnace12powered with alternating current, a different type of melting or heating furnace, such as an induction furnace, a ladle furnace or other.

The apparatus10acan comprise a first transformer14, located downstream of the electricity grid11, for example a high voltage/medium voltage (HV/MV) transformer configured to transform high voltage energy into medium voltage energy, which can be connected to the electricity grid11by means of a conductor17of the traditional type.

The electric apparatus10aalso comprises a power supply system19in alternating current that powers the electric arc furnace12, which can be connected to the first transformer14by means of a segment of line27, on which there are an alternating mains voltage and mains current.

According to some variants, the power supply system19can be connected directly to the electricity grid11by the connection means.

The power supply system19can comprise a first part15configured to transform the mains current and voltage from alternating current into direct current, and a second part16configured to transform the current and voltage from direct current into alternating current to be supplied to the electric furnace12, the two parts being connected to each other by means of an intermediate circuit38which works in direct current and which can be manufactured at least in part with one or more superconductor cables.

This allows the electrical energy to be transferred from the first part15to the second part16of the power supply system19substantially without losses, and it is therefore possible to separate the first part15and the second part16from each other as a function of the construction or logistical needs of the plant, distancing them even by hundreds of meters or a few kilometers.

The power supply system19can comprise at least one transformer33connected to the segment of line27for supplying mains voltage and alternating current, and configured to transform the supply mains voltage and alternating current into a base voltage and alternating current

According to some embodiments, the electricity grid11can be three-phase. The mains voltage and the mains current have a predefined mains frequency. The mains frequency is a value chosen between 50 Hz and 60 Hz, that is, based on the frequency of the electricity grid of the country where the electric furnace12is installed.

The transformer33can comprise a transformer primary34magnetically coupled to at least one transformer secondary35.

The transformer33can comprise a plurality of transformer secondaries35magnetically coupled to the transformer primary34.

The solution of providing various transformer secondaries35allows to reduce the impact of disturbances grid-side, or to reduce the harmonic content and reactive power exchanged on the grid by the combination of the transformer33and the rectifier36.

According to some embodiments, a transformer secondary35is provided for each phase of the electricity grid11.

The base voltage and current supplied by the transformer33have a base voltage, a base current, and a base frequency, which are predefined and set by the design characteristics of the transformer33itself.

In particular, the base frequency is substantially equal to the mains frequency identified above.

The base voltage and the base current, on the other hand, are correlated respectively to the mains voltage and to the mains current by the transformation ratio of the transformer33itself.

The transformer33, which for example can be of the multi-tap type, can be provided with adjustment devices, not shown, provided to selectively adjust the electrical transformation ratio of the transformer33in relation to specific requirements.

The power supply system19also comprises at least one rectifier36disposed downstream of the transformer33along the electric line13a, in particular connected to the transformer secondary35.

According to some embodiments, for example described with reference toFIGS.3and4, the power supply system19can comprise a plurality of rectifiers36connected to the transformer33and configured to transform the base voltage and base alternating current into direct voltage and current.

A rectifier36is preferably provided connected downstream of each transformer secondary35.

Specifically, the rectifiers36allow to rectify the base voltage and the base alternating current, into respective direct voltages and currents.

The rectifiers36can be selected from a group comprising a diode bridge and a thyristor bridge.

In accordance with a possible solution, the rectifiers36comprise devices, for example chosen from a group comprising Diodes, SCR (Silicon Controlled Rectifier), GTO (Gate Turn-Off thyristor), IGCT (Integrated Gate-Commutated Thyristor), MCT (Metal-Oxide Semiconductor Controlled Thyristor), BJT (Bipolar Junction Transistor), MOSFET (Metal-Oxide Semiconductor Field-Effect Transistor), IGBT (Insulated-Gate Bipolar Transistor) and SiC (Silicon Carbide Device).

The one or more transformer secondaries35can be connected to the corresponding rectifier36by means of a segment of line28made with at least one superconductor cable.

The power supply system19can comprise a plurality of converters37connected to the rectifiers36and configured to convert the direct voltage and current into a voltage and alternating current for powering the electrodes of the electric arc furnace12.

Preferably, a converter36is provided connected downstream of each rectifier35.

The converters37can comprise devices, for example chosen from a group comprising SCR (Silicon Controlled Rectifier), GTO (Gate Turn-Off thyristor), IGCT (Integrated Gate-Commutated Thyristor), MCT (Metal-Oxide Semiconductor Controlled Thyristor), BJT (Bipolar Junction Transistor), MOSFET (Metal-Oxide Semiconductor Field-Effect Transistor), IGBT (Insulated-Gate Bipolar Transistor) and SiC (Silicon Carbide Device).

In accordance with possible solutions, the one or each rectifier36is connected to a converter37by means of at least one intermediate circuit38which works in direct current.

The one or more transformers33and the one or more rectifiers36are comprised in the first part15of the power supply system19, while the one or more rectifiers36are comprised in the second part16of the power supply system19.

The intermediate circuit38is configured to store direct electrical energy and to generate a separation between the second part16and the first part15of the power supply system19, and in particular, in the example case, between the electrodes of the electric arc furnace12and the rectifiers36, and therefore with the electricity grid11.

In particular, the rapid power fluctuations resulting from the metal melting process are partly filtered through the intermediate circuit38, reducing the impact on the electricity grid11side.

This intermediate circuit38comprises one or more segments of line31which are made with at least one superconductor cable.

Thanks to the use of one or more of such segments of line31made with at least one or more superconductor cables, it is possible to increase the distances between the means for connection to the electricity grid11and the electric arc furnace12, which are generally comprised between a few meters and about 20-40 m in traditional plants, according to different needs of the plant, for example expansion, addition or separation of components or parts, or other.

These superconductor cables are characterized by having much smaller section sizes, as well as practically zero losses in direct current DC and extremely low losses in alternating current AC, compared to conductor cables normally used in the sector.

For example, such superconductor cables can be at least partly made of Magnesium Diboride, or other alloys developed to achieve the super conduction. The cross-sections of superconductor cables are very small compared to the sections of copper conductor cables used in the sector; therefore, for the same section, a superconductor cable transfers much more current than a traditional cable.

For example, in the sizing of power cables, these go from a capacity of about 1.5 A/mm2for copper to about 1000 A/mm2for direct current DC superconductor cables.

Preferably, the segments of line31made with one or more superconductor cables are forcibly cooled down to temperatures of 20-30 k (−240° C.). This in fact takes the resistance of the segment of line31to negligible values, even to practically zero in direct current DC, allowing a favored passage of enormous quantities of electrons and therefore the transfer of high quantities of current.

This cooling can be carried out, for example, by means of a coaxial coating of the segments of line31which refrigerant fluids travel through, such as for example liquid gases such as nitrogen or helium, which can be made with another simple or corrugated pipe made of steel.

The superconductor cables which these segments of line31are made of can also be more or less rigid, so as to allow straight or curved underground installations.

If there is a rectifier36and a converter37for each phase of the grid, all the rectifiers36and the converters37can share the same intermediate circuit38made with superconductor cables.

In the power supply system19shown inFIGS.1-3, each of the units comprising the transformer33with one or more rectifiers36and one or more converters37as a whole defines a power supply module39.

The power supply system19can provide between 1 and “n” power supply modules, as a function of usage requirements, or it can be provided with a plurality of power supply modules39, connected in parallel to each other, to the electricity grid11and to the electric arc furnace12.

In the embodiment shown by way of example inFIG.3, a single power supply module39is shown, while inFIGS.1and2, 3 modules are shown indicated with numbers 1, 2, n, where n can be equal to 3 or greater, for example 10, 12, 24, 40, 48, 60 or intermediate values, or greater than 60.

The combination of several power supply modules39allows to obtain a power supply system19which can be scaled in size in relation to the specific size of the electric arc furnace12to be powered.

Downstream of each of the converters37, there can also be provided an inductor40, which contributes to the overall reactance of the power supply system19.

The segments of line30located downstream of the converters37and upstream of the electric arc furnace12can be at least partly made with at least one superconductor cable.

According to some embodiments, the segment of line27that connects the high voltage/medium voltage transformers14and the medium voltage/medium voltage transformers33to each other can also be made with at least one superconductor cable.

Thanks to the use of superconductor cables, the segment of line27can be made according to any length whatsoever, from a few and up to one or more kilometers. Currently, in the electric apparatuses for powering electric arc furnaces, this segment of line27is of the order of a few tens or a hundred meters.

The segment of line30that connects each converter37to the electric furnace12, the length of which is currently equal to about 30 m, can also be made with a considerably greater length, thanks to the use of one or more superconductor cables, even of one or more kilometers.

In the example of an electric apparatus10b,10cofFIGS.2and3, the power supply system19is substantially divided into two separate buildings41and42, for example the building41can be an electric substation while the building42can be the steel plant.

In particular, a first part15of the power supply system19configured to transform the mains current and voltage from alternating current into direct current can be disposed in the first building41, while a second part16of the power supply system19configured to transform the current and voltage from direct current into alternating current to be supplied to the electric furnace12can be disposed in the second building42, possibly together with the electric furnace12.

The first part15and the second part16are connected to each other by the segments of line31in direct current made with one or more superconductor cables.

We have therefore assumed that the one, or each, power supply module39of the power supply system19is divided into two separate parts, a first part39acontained in the first building41and a second part39bcontained in the second building42. These parts39aand39bare connected by the segments of line31made with at least one superconductor cable.

An electric line13ddevelops starting from the electricity grid11, the electrical continuity of which is guaranteed between the rectifiers36of the building41and the converters of the building42, by means of the segments of line31. These segments of line31which go from one building to the others are in particular segments of line31in direct current that define the intermediate circuit38, with losses practically equal to zero. These segments of line31are made with one or more superconductor cables, therefore the distance between the two buildings41and42can be chosen at will and can even be of the order of one or more kilometers.

By way of example, we have assumed that the first part39apositioned in the first building41comprises the transformers33and the rectifiers36, while the second part39bpositioned in the second building42comprises the converters37, the inductors40and the segments of line30which carry the current to the electric arc furnace12.

These segments of line30, as seen for the example ofFIG.1, can also be made with one or more superconductor cables.

As previously mentioned, in order to function properly, the superconductor cables of the various segments of line27,28,30,31have to be cooled in a very forceful manner.

This can be done using, for example, cryogenic cooling units suitably positioned in the electric apparatus10a-10c. The cooling mean, for example in the case of superconductors made of Magnesium Diboride, is normally helium.

However, other gases such as oxygen, nitrogen, hydrogen and/or combinations thereof are conceivable as a function of the type of material which the superconductor cables consist of.

Adopting superconductor cables can also be done for applications that require high currents, such as for example induction melting or heating furnaces, or other.

It is clear that modifications and/or additions of parts may be made to the electric apparatus as described heretofore, without departing from the field and scope of the present invention.

It is also clear that, although the present invention has been described with reference to some specific examples, a person of skill in the art shall certainly be able to achieve many other equivalent forms of electric apparatus, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.

In the following claims, the sole purpose of the references in brackets is to facilitate reading: they must not be considered as restrictive factors with regard to the field of protection claimed in the specific claims.