Converter Device and Electric Power Supply Apparatus

Abstract

Converter device configured to convert direct voltage and current into alternating voltage and current to be supplied to a load (L). The converter device comprises a bank (11) of capacitors (12), a plurality of power semiconductors (13), a heat sink (14) and a casing (15).

Claims

1. Converter device configured to convert direct voltage and current into alternating voltage and current to be supplied to a load (L), wherein the converter device comprises a bank (11) of capacitors (12), connectable, during use, to a direct current power supply circuit, a plurality of power semiconductors (13) connected to the bank of capacitors (12) and configured to be selectively turned on and off in order to allow the generation of a sinusoidal current wave toward an output (15b), a heat sink (14) on which said power semiconductors (13) are installed and which is configured to dissipate the heat generated by them, and a casing (15) which encloses inside it at least the bank (11) of capacitors (12), the heat sink (14) and the power semiconductors (13), characterized in that at least one of either the heat sink (14) or the capacitors (12) are floating with respect to the casing (15) and to an earth connection (G) of said casing (15).

2. Converter device as in claim 1, characterized in that both said heat sink (14) and said capacitors (12) are floating with respect to said casing (15).

3. Converter device as in claim 1 or 2, characterized in that said heat sink (14) and/or said capacitors (12) are electrically isolated with respect to said casing (15).

4. Converter device as in claim 1 or 2, characterized in that it comprises at least a first high-impedance component (16) connected between said heat sink (14) and said casing (15).

5. Converter device as in claim 1 or 4, characterized in that said capacitors (12) are film-type capacitors and comprise a containing body (17) of metal material, and said converter device comprises a plurality of second high-impedance components (18) each connected between the containing body (17) of a respective capacitor (12) and the earth connection (G) connected to said casing (15).

6. Converter device as in claim 4 or 5, characterized in that said at least one first component (16) and/or said second high-impedance components (18) have an impedance comprised between 5000 and 15000.

7. Converter device as in any claim from 4 to 6, characterized in that said at least one first component (16) and/or said second components (18) have an impedance comprised between 8000 and 12000.

8. Converter device as in any claim hereinbefore, characterized in that it comprises at least one low-pass electrical filter (19), connected between an output connector (15b) suitable to be connected, during use, to the load (L) to be powered, and the earth (G).

9. Apparatus to supply electric power to a high-power ohmic-inductive load (21), comprising: a transformer (25) connected to power grid (26) that supplies an alternating mains voltage (Ur) and an alternating mains current (Ir), the transformer (25) being configured to transform the alternating mains voltage (Ur) and the alternating mains current (Ir) into an alternating base voltage (Ub) and an alternating base current (Ib); a plurality of rectifiers (29) connected to the transformer (25) and configured to transform the alternating base voltage (Ub) and alternating base current (Ib) into direct voltage and electric current, characterized in that it also comprises: a plurality of converter devices (10) as in any previous claim from 1 to 8, connected on one side to the rectifiers (29), and on the other to the load (21), and configured to convert direct voltage and current into a voltage (Ua) and an alternating supply current (la), to be supplied to the load (21); a control and command unit (31) configured to control and command the functioning of the converter devices (32) and regulate the voltage (Ua) and the supply current (la) over time.

10. Electric power supply apparatus as in claim 9, characterized in that it comprises a low-pass electrical filter (30) connected between an output of the converter devices (10) and the earth (G), and configured to attenuate, or eliminate, possible current fluctuations directed toward the earth.

11. Electric power supply apparatus as in claim 10, characterized in that said electrical filter (30) is an RC filter of the three-phase type, and is inserted on the output phases (L1, L2, L3) which are connected, during use, to the load (21).

12. Electric power supply apparatus as in claim 10 or 11, characterized in that said electrical filter (30) is an RC filter provided with a resistive component (R) and a capacitive component (C) and comprises dissipation means (36) configured to dissipate the thermal energy generated by one or by both the resistive (R) and capacitive (C) components and reduce their temperature.

13. Electric power supply apparatus as in claim 12, characterized in that said electrical filter (30) comprises temperature measurement sensors (37) associated with one or more of the resistive (R) and/or capacitive (C) components and configured to measure their temperature.

14. Electric power supply apparatus as in any claim from 9 to 13, characterized in that said control and command unit (31) is provided with regulation devices (32) configured to regulate an electric supply frequency (fa) of said supply voltage (Ua) and supply current (la), in a manner independent of a mains frequency (fr) of said power grid (26), and obtain a regulation of the reactance of said power supply apparatus (10).

15. Electric power supply apparatus as in claim 14, characterized in that said regulation devices (32) comprise a hysteresis modulator, or a PWM (Pulse-Width-Modulation) modulator.

16. Electric power supply apparatus as in any claim from 9 to 15, characterized in that it comprises a plurality of power supply modules (34), each comprising a transformer (25), a rectifier (29), and a converter devices (10) connected in parallel to each other, to the power grid (26) and to the load (21).

17. Electric arc furnace comprising a container (22) or shell into which metal material (M) is introduced to be subsequently melted and a plurality of electrodes (23) configured to strike an electric arc through the metal material (M) and melt it, characterized in that it comprises an electric power apparatus (20) as in any claim from 9 to 16 connected between a power grid (26) and said electrodes (23).

Description

ILLUSTRATION OF THE DRAWINGS

[0068] These and other aspects, characteristics and advantages of the present invention will become apparent from the following description of some embodiments, given as a non-restrictive example with reference to the attached drawings wherein:

[0069] FIG. 1 is a schematic view of a converter device according to some embodiments described here;

[0070] FIG. 1a is a schematic view of a component of the converter device of FIG. 1 according to a first embodiment;

[0071] FIG. 1b is a schematic view of a component of the converter device of FIG. 1 according to a variant embodiment;

[0072] FIG. 1c is a schematic view of another component of the converter device of FIG. 1 according to a first embodiment;

[0073] FIG. 1d is a schematic view of another component of the converter device of FIG. 1 according to a variant embodiment;

[0074] FIG. 2 is a schematic view of an apparatus to supply electric power to a high-power load applied to an electric arc furnace.

[0075] 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.

DESCRIPTION OF EMBODIMENTS

[0076] 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.

[0077] Some embodiments described here with reference to FIG. 1 concern a converter device, indicated with reference number 10, suitable to convert direct voltage and current into alternating voltage and current.

[0078] The converter device 10 can be used, for example, for medium voltage applications that require high power.

[0079] The converter devices 10 according to the invention can advantageously be used both individually and also in combination with a plurality of other converter devices 10.

[0080] Some embodiments described here also concern an electric power supply apparatus, indicated as a whole with reference number 20 (FIG. 2), configured to supply a current and a voltage in alternating current suitable to power a load 21 that requires high power, in particular of the ohmic-inductive type.

[0081] FIG. 2 shows, by way of example, the application of the power supply apparatus 20 to a load corresponding to an electric arc furnace 21, but this power supply apparatus 20 can also be used to power loads of different types, for example a ladle furnace, or a submerged arc furnace.

[0082] According to some embodiments, the converter device 10 comprises a capacitor bank 11 which includes a plurality of capacitors 12 connected together in series and/or parallel, configured to accumulate electrical energy in direct current.

[0083] The converter device 10 also comprises a plurality of power semiconductors 13 connected to the capacitor bank 11 and configured to be selectively turned on and off to allow the generation of a sinusoidal current wave toward an output.

[0084] The converter device 10 also comprises a dissipator device 14, on which the power semiconductors 13 are attached and installed, which is configured to dissipate the heat generated by the latter during functioning.

[0085] According to some embodiments, the heat sink 14 is of the water cooled type, although it is not excluded that for certain applications a heat sink 14 cooled with forced air may be used.

[0086] In accordance with one possible solution, the power semiconductors 13 comprise devices 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), and IGBT (Isolated-Gate Bipolar Transistor).

[0087] The converter device 10 also comprises a casing 15, that is, a metal shell, which encloses inside it the capacitor bank 11, the heat sink 14 and the power semiconductors 13.

[0088] The casing 15 is provided with input 15a and output 15b connectors respectively connectable to an upstream circuit, for example an electric power supply grid, and to a downstream circuit, for example connected to a load L or user device 21 to be powered.

[0089] According to some embodiments, the casing 15, during use, can be connected to an earth connection G for safety reasons.

[0090] The earth connection, depending on requirements, can be the real safety earth or a functional earth. By functional earth we mean an earth that guarantees the functioning of the electronic devices and that is sized as a function of the devices to be protected, but that does not guarantee the safety of operators according to regulations.

[0091] According to one aspect of the present invention, at least one of either the heat sink 14 or the capacitor bank 11 has a floating potential with respect to the casing 15 and therefore to the earth connection G connected to it.

[0092] According to further embodiments, both the heat sink 14 and also the capacitor bank 11 are “floating” with respect to the casing 15 and therefore to the earth connection G.

[0093] With the term “floating” or “floating potential” we mean that the heat sink 14 and/or the battery 11 of capacitors 12 are at least partly isolated with respect to the casing 15, that is, they are electrically isolated with respect to the casing 15 and therefore to the earth connection G connected to it, or they are connected to the casing 15 by means of high-impedance components or circuits, thus preventing or at least considerably limiting the generation of a parasitic current to earth G.

[0094] According to some embodiments, at least one of either the heat sink 14 or the bank 11 of capacitors 12 is electrically isolated with respect to the casing 15, that is, there is no circulation of direct current between them and the casing 15 (FIGS. 1a and 1c).

[0095] According to possible variants, at least one of either the heat sink 14 or the bank of capacitors 12 is connected to the casing 15 by means of a high-impedance component (FIGS. 1b and 1d).

[0096] According to some embodiments, the converter device 10 comprises at least a first high-impedance component 16 connected between the heat sink 14 and the earth connection G to which the casing 15 is connected (FIG. 1d).

[0097] According to some embodiments, the first high-impedance component 16 can have an impedance comprised between 5000 and 15000.

[0098] According to further embodiments, the first high-impedance component 16 can have an impedance comprised between 8000 and 12000.

[0099] According to some embodiments, the capacitors 12 are film type capacitors, provided with a containing body 17 made of metal material, for example aluminum.

[0100] According to some embodiments, the converter device 10 comprises a plurality of second high-impedance components 18 each connected between the containing body 17 of a capacitor 12 and the earth connection G to which the casing 15 is connected (FIG. 1b).

[0101] In this way, the capacitors 12 are substantially isolated with respect to the casing 15 of the converter device 10 and consequently the possible unwanted currents to earth G that are generated have a substantially negligible peak value.

[0102] According to some embodiments, the second high-impedance components 18 can each have an impedance comprised between 5000 and 15000.

[0103] According to further embodiments, the second high-impedance components 18 can each have an impedance comprised between 8000 and 12000.

[0104] According to some embodiments, both the heat sink 14 and also the capacitors 12 are connected to the casing 15 and therefore to earth G, by means of respective high-impedance components 16, 18.

[0105] According to further embodiments, the converter device 10 comprises at least one electrical filter 19 connected between an output connection of the converter device 10 connectable, during use, to the load L to be powered, and the earth connection G.

[0106] The electrical filter 19 comprises an RC filter provided with a resistive component R and a capacitive component C located in series with each other, and is configured to act as a low-pass filter, eliminating possible current oscillations due to distributed parasitic inductances and capacitances.

[0107] With reference to FIG. 2, the electric furnace 21 comprises a container 22, or shell, into which metal material M is introduced to be subsequently melted.

[0108] The electric furnace 21 is also provided with a plurality of electrodes 23, in the case shown three electrodes 23, configured to strike an electric arc through the metal material M and melt it.

[0109] According to some embodiments of the present invention, the electrodes 23 are installed on movement devices 24 configured to selectively move the electrodes 23 toward/away from the metal material M.

[0110] The movement devices 24 can be chosen from a group comprising at least one of either a mechanical actuator, an electric actuator, a pneumatic actuator, a hydraulic actuator, an articulated mechanism, a kinematic mechanism, similar and comparable members or a possible combination of the above.

[0111] In accordance with one possible solution of the present invention, in the event that there are three electrodes 23, each of them is connected to a respective power supply phase L1, L2, L3 of the power supply apparatus 20.

[0112] In accordance with some embodiments of the present invention, the power supply apparatus 20 comprises at least one transformer 25 connected to a power grid 26 for supplying a voltage and an alternating mains current, the transformer 25 being configured to transform the voltage and alternating supply current into a voltage and alternating base current.

[0113] According to one possible solution of the invention, the power grid 26 can be three-phase.

[0114] In accordance with some embodiments of the invention, the mains voltage Ur and the mains current Ir have a predefined mains frequency fr.

[0115] In accordance with possible solutions, the mains frequency fr is a value chosen between 50 Hz and 60 Hz, that is, based on the frequency of the power grid of the country where the furnace is installed.

[0116] In accordance with possible solutions of the present invention, the transformer 25 can comprise a transformer primary 27 magnetically coupled to at least one transformer secondary 28.

[0117] In accordance with one possible solution of the invention, the transformer 25 can comprise a plurality of transformer secondaries 28 magnetically coupled to the transformer primary 27. This solution allows to reduce the impact of disturbances grid side, that is, to reduce the harmonic content and the reactive power exchanged in the grid by the combination of the transformer 25 and the rectifier 29.

[0118] Preferably there are provided three phases connected to the transformer secondaries 28, but the number of phases could also be smaller or greater. According to some embodiments, the number of phases can vary between 1 and n, where n, for example, is an integer up to twenty, or even greater than twenty.

[0119] The base electrical energy supplied by the transformer 25 has a base voltage Ub, a base current Ib, and a base frequency fb, which are predefined and set by the design characteristics of the transformer 25 itself.

[0120] In particular, the base frequency fb is substantially equal to the mains frequency fr identified above.

[0121] The base voltage Ub, the base current Ib, on the other hand, are correlated respectively to the mains voltage Ur, and to the mains current Ir by the transformation ratio of the transformer 25 itself.

[0122] The transformer 25, for example of the multi-tap type, can be provided with regulating devices, not shown, provided to selectively regulate the electrical transformation ratio of the transformer 25 in relation to specific requirements.

[0123] The apparatus 20, according to the present invention, also comprises a plurality of rectifiers 29 connected to the transformer 25 and configured to transform the voltage and alternating base current into direct voltage and current.

[0124] Specifically, the rectifiers 29 allow to rectify the voltage Ub and the alternating base current Ib, into respective direct voltages and currents.

[0125] The rectifiers 29 can be chosen from a group comprising a diode bridge and a thyristor bridge.

[0126] In accordance with one possible solution, the rectifiers 29 comprise 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) and IGBT (Isolated-Gate Bipolar Transistor).

[0127] In accordance with another aspect of the invention, the apparatus 20 comprises a plurality of converter devices 10 connected to the rectifiers 29 and configured to convert the direct voltage and current into a voltage and alternating current for powering the electrodes 23.

[0128] The converter devices can be converter devices 10 according to the invention, in which the capacitors 12 and/or the heat sink 14 are floating with respect to the earth connection G of the casing 15 of the respective converter device 10.

[0129] The converter devices 10 are connected to the electrodes 23 of the melting furnace 21 and to a control and command unit 31 configured to control and command the functioning of the converter devices 10 and to regulate the alternating power supply to the electrodes 23 over time.

[0130] According to some embodiments, the apparatus 20 comprises an electrical filter 30 connected between an output of the converter devices 10 and the load to be powered, in the example case the electrodes 23 of the furnace 21, and configured to act as a low-pass filter and dampen, or eliminate, possible oscillations of the earth current during the switching of the semiconductor devices 13, which are generated by the components of parasitic capacitance and inductances of the converter devices 10, or possibly of other components of the apparatus 20.

[0131] According to some embodiments, the electrical filter 30 can be an RC filter connected in correspondence with an output of the converter devices 10.

[0132] According to some embodiments, the electrical filter 30 can be used as an alternative to possible electrical filters 19 of the individual converter devices 10.

[0133] According to possible solutions, an electrical filter 30 could also be provided, used in addition to possible electrical filters 19 associated with respective converter devices 10.

[0134] According to some embodiments, the electrical filter 30 is of the three-phase type, and is inserted on the output phases L1, L2, L3 which are connected to the load, that is, to the electrodes 23.

[0135] The combination of the electrical filter 30 connected at the output of the converter devices 10 and of the high-impedance components 16, 18 inserted inside the converter devices 10 themselves, allow both to eliminate the oscillations of the current, and also to limit, if not eliminate, the peak of the current itself to earth.

[0136] This configuration therefore allows to use a large number of converter devices, even greater than 60, without the risk of malfunctioning of the control devices due to high current peaks generated by parasitic currents, thus making the electric power supply apparatus 20 efficient and reliable.

[0137] According to some embodiments, the resistive component R and/or the capacitive component C of the electrical filters 19, 30 can be sized as a function of the application of the converter device 10 and the characteristics of the load to be powered.

[0138] According to some embodiments, the resistive component R and the capacitive component C can be regulated by means of the control and command unit 31 in order to modify the respective resistance and capacitance values in such a way as to increase or reduce the intensity of current that flows through them.

[0139] According to some embodiments, the electrical filter 19, 30 can comprise dissipation means 36 configured to reduce the temperature of the components of the RC filter.

[0140] By way of example, the dissipation means 36 can comprise fans, or other means for moving the air, dissipation fins, or suchlike.

[0141] According to some embodiments, the electrical filter 19, 30 can also comprise temperature measurement means, for example sensors 37 associated with one or more of the resistive R and/or capacitive C components.

[0142] By way of example, the temperature measurement sensors 37 can comprise thermocouples associated with one or more of either the resistive component R or the capacitive component C.

[0143] According to some embodiments, the control and command unit 31 can receive from the sensors 37 the detected data and possibly command the activation/deactivation of the ventilation devices 36 as a function of the data received so as to maintain thermal conditions suitable to guarantee an effective functioning of the electrical filter 19, 30.

[0144] According to some embodiments, the control and command unit 31 also controls the converter devices 10 so as to selectively set the parameters of the voltage and alternating supply current as above.

[0145] In accordance with one aspect of the present invention, the control and command unit 31 is provided with regulation devices 32 configured to regulate the electric supply frequency fa of the voltage and alternating supply current and obtain a simultaneous variation of the reactance value of the power supply circuit of the electrodes.

[0146] Specifically, the supply voltage and current have a supply voltage Ua, and a supply current 1a, which are selectively regulated in relation to the melting powers involved.

[0147] In accordance with possible solutions of the present invention, the regulation devices 32 can comprise, by way of example only, a hysteresis modulator, or a PWM (Pulse-Width-Modulation) modulator.

[0148] These types of modulator can be used to command the semiconductor devices of the rectifiers 29 and of the converter devices 10. These modulators, suitably controlled, generate voltage or current values to be actuated to the electrodes 23. In particular, the modulator processes such voltage and current values and produces commands for driving at least the rectifiers 29 and the converters 10 so that the voltage and current values required by the control are present at the terminals for connection to the electrodes 23. The voltages and currents to be actuated are the result of operations performed by the control and command unit 31 on the basis of the quantities read by the process and on the basis of the process model.

[0149] In accordance with possible solutions, the rectifiers 29 can be connected to the converter devices 10 by means of at least one intermediate circuit 33 which works in direct current.

[0150] The intermediate circuit 33 is configured to store direct electrical energy and generate a separation between the load, in this specific case the electrodes 23, and the rectifiers 29, and therefore with the power grid 26.

[0151] In particular, the rapid power fluctuations resulting from the process are partly filtered by means of the intermediate circuit 33, reducing the impact on the power grid 26 side.

[0152] The control and command unit 31 can also be configured to regulate the supply voltage Ua and supply current 1a parameters generated by the converter devices 10 and supplied to the electrodes 23.

[0153] Some solutions of the present invention provide that the control and command unit 31 is also connected, in turn, to the movement device 24 in order to allow an adjustment of the position of the electrodes 23 in relation to the different steps of the melting process.

[0154] In particular, the electrodes 23 are moved by the movement device 24 in order to track the position of the material and therefore modify the length of the arc.

[0155] In this way, the control and command unit 31 can manage and command, in relation to the specific steps of the process, at least the following parameters: supply voltage Ua, supply current 1a, electric supply frequency fa, and position of the electrodes 23. The high possibility of controlling the different parameters allows to optimize the transfer of energy to the process and at the same time reduce the effects on the power grid 26 deriving from the rapid power variations on the furnace side.

[0156] According to possible solutions, the transformer 25, the rectifiers 29, connected to the transformer 25, and the converter devices 10 together define a power supply module 34.

[0157] In accordance with one possible embodiment of the invention, the apparatus 20 can be provided with a plurality of power supply modules 34, connected in parallel to each other, to the power grid 26 and to the furnace 21.

[0158] The combination of several power supply modules 34 allows to obtain an apparatus 20 that can be scaled in size in relation to the specific size of the electric furnace 21 to be powered.

[0159] According to embodiments, the number of power supply modules 34 can vary from 2 to m, where m is an integer which can be ten, twelve, twenty, forty, sixty, or even greater than sixty.

[0160] The power supply modules 34 can be connected each to an electrode 23, in order to supply the letter with electric energy. There could be provided more than one power supply module 34 for each electrode 23.

[0161] Therefore, according to the number of power supply modules 34, the apparatus 20 can comprise a high number of converter devices 10, up to sixty or even more.

[0162] In accordance with one possible solution, the control and command unit 31 is connected to all the power supply modules 34 in order to control at least the respective converter devices 10, so that each module supplies the same values of supply voltage Ua, supply current 1a, and electric supply frequency fa to the load. In this way, it is possible to prevent malfunctions of the entire system.

[0163] In accordance with one possible solution, the apparatus 20 can comprise an inductor 35 configured to obtain the desired overall reactance of the apparatus.

[0164] The inductor 35 can be connected downstream of the converter devices 10 and is sized so as to achieve the desired total equivalent reactance. In this way, it is possible to obtain an overall reactance that is given by the contribution of the inductor 35 and by the reactance introduced by the conductors that connect the system to the load.

[0165] According to some embodiments, the inductor 35 can be connected downstream of the low-pass electrical filter 30.

[0166] In general, the inductance is a (design) parameter that cannot be modified once the component is built.

[0167] By modifying the frequency (with respect, for example, to the 50 Hz of the grid) it is possible, with the same inductance, to change the reactance value that the component has in the circuit and therefore reach the desired total equivalent reactance value.

[0168] By regulating the frequency during the different steps of the process, with the present invention it is therefore possible to optimize the electrical parameters in each step. First of all, the entity (and therefore the cost) of the inductance can be contained, using it to the best of its ability during refining.

[0169] Through the electrical topology adopted for the converters it is also possible to preserve the power grid from disturbances due to the melting process (flicker reduction, harmonics, Power Factor, etc.), while at the same time guaranteeing the stability of the arc in all steps.

[0170] Furthermore, the possibility of modifying the supply frequency of the electrodes with respect to the mains frequency makes it easier to size the inductive components in conditions where spaces/costs are limited, it improves their use of the conductors, reducing resistance and therefore system losses.

[0171] In the case of an electric arc furnace, for example, with the same arc impedance, increasing the frequency increases the inductive reactance and decreases the equivalent power factor toward the load, which improves the stability of the arc (useful when, for example, the scrap is not yet melted, and the arc is not very protected) preventing it from extinguishing.

[0172] It is clear that modifications and/or additions of parts may be made to the converter device 10 and to the electric power supply apparatus 20 as described heretofore, without departing from the field and scope of the present invention.

[0173] 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 converter device 10 and electric power supply apparatus 20, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.

[0174] 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.