BRIEF DESCRIPTION OF THE DRAWINGS
These and further objectives, advantages and features of the present invention are evident from the following detailed description of examples of embodiment in conjunction with the drawing. In the figures:
FIG. 1 shows a first exemplary embodiment of an arc furnace power supply device,
FIG. 2 shows a second exemplary embodiment of an arc furnace power supply device,
FIG. 3 shows a third exemplary embodiment of an arc furnace power supply device,
FIG. 4 shows a fourth exemplary embodiment of an arc furnace power supply device.
The reference symbols used in the drawing and their significance are summarily listed in the reference symbol list. As a matter of principle the same parts are provided with the same reference symbols in the figures. The described exemplary embodiments are by way of example, but are not meant to be restrictive.
DETAILED DESCRIPTION
In FIG. 1 is represented a first exemplary embodiment of the arc furnace power supply device. In this the arc furnace power supply device comprises a rectifier 1, which rectifier can be connected on its alternating voltage side with an electrical alternating voltage supply network 2. The connection can be effected directly via a power supply switch, not represented in the interests of clarity, and/or via one or a plurality of transformers with appropriate voltage levels. On the direct voltage side the rectifier 1 according to FIG. 1 is connected with a direct voltage circuit 3. The direct voltage circuit 3 can be formed by one or a plurality of capacitive energy stores, as shown in FIG. 1 in an exemplary manner. Moreover the arc furnace power supply device has an inverter 4, which inverter 4 on its direct voltage side is connected with the direct voltage circuit 3 and on its alternating voltage side with at least one arc electrode 5, wherein in FIG. 1 in an exemplary manner three arc electrodes connected with the inverter 4 are provided. The exemplary inverter 4 is configured as an inverter that applies a rectangular alternating voltage to the arc electrode. The inverter is thus configured such that it generates a rectangular alternating voltage, which is then applied to the arc electrode(s) 5. As a result of the rectangular alternating voltage applied to the arc electrode 5 by means of the inverter 4 the arc resistance reduces in a significant manner as the arc electrode current passes through zero, and the current gradient di/dt increases as the arc electrode current passes through zero, whereby the arc can advantageously be stabilised and for this reason burns more evenly.
The frequency of the rectangular alternating voltage can correspond essentially to the frequency of the alternating voltage in the electrical alternating voltage supply network 2, whereby a particularly stable and evenly burning arc can be achieved.
According to FIG. 1 the inverter 4 for each arc electrode 5 has a respective inverter branch pair 6, wherein each inverter branch pair 6 has two controllable bidirectional power semiconductor switches S1, S2 connected in series, and the arc electrode 5 in question is connected with the connection point between the two controllable bidirectional power semiconductor switches S1, S2 connected in series. In the event of a plurality of arc electrodes 5 the respective inverter branch pairs can be connected in parallel. Moreover each inverter branch pair 6 can be connected in parallel with the direct voltage circuit 3. Each of the controllable bidirectional power semiconductor switches S1. S2 can be formed by a gate turn-off thyristor, or by a bipolar transistor with an insulated gate electrode (IGBT), or by an integrated thyristor with a commutated control diode (IGCT), and by a diode connected in antiparallel with the gate turn-off thyristor, or bipolar transistor, or thyristor with commutated control diode. It is however also conceivable, for example, to embody a previously cited controllable bidirectional power semiconductor switch S1. S2 as a power MOSFET with an additional diode connected in antiparallel. By means of the inverter branch pair 6 in question it is advantageously possible to adjust the rectangular alternating voltage on the respective arc electrode 5 with respect to the amplitude and phase, and thereby to influence the stability and even burning of the arc appropriately. Additionally according to FIG. 4 in an exemplary manner, in a fourth exemplary embodiment of the arc furnace power supply device, six arc electrodes 5 connected with the inverter 4 can be provided, so that six inverter branch pairs 6 are then present.
According to FIG. 1 and FIG. 4, the rectifier 1 of the electrical alternating voltage supply network 2 has a series circuit for each phase R. S, T, consisting of two controllable unidirectional power semiconductor switches S3, S4. The series circuits in question are here connected in parallel, and are connected in parallel with the direct voltage circuit 3. Each of the controllable unidirectional power semiconductor switches S3. S4 can be formed by a gate turn-off thyristor or by a bipolar transistor with an insulated gate electrode (IGBT), or by an integrated thyristor with a commutated control diode (IGCT). It is however also conceivable, for example, to design a previously cited controllable unidirectional power semiconductor switch S3, S4 as a power MOSFET.
In FIG. 2 is shown a second exemplary embodiment of the arc furnace power supply device. In contrast to the first exemplary embodiment according to FIG. 1, the rectifier 1 has a series circuit for each phase R. S, T of the electrical alternating voltage supply network 2, consisting of two controllable bidirectional power semiconductor switches S5, S6. Each of the controllable bidirectional power semiconductor switches S5. S6 can be formed by a gate turn-off thyristor, or by a bipolar transistor with an insulated gate electrode (IGBT), or by an integrated thyristor with a commutated control diode (IGCT), and by a diode connected in antiparallel with the gate turn-off thyristor, or bipolar transistor, or thyristor with commutated control diode. It is however also conceivable, for example, to embody a previously cited controllable bidirectional power semiconductor switch S5, S6 as a power MOSFET with an additional diode connected in antiparallel. A rectifier 1 implemented in such a manner by means of the previously cited controllable bidirectional power semiconductor switches S5, S6 with advantage generates on the alternating voltage side and direct voltage side only very small harmonics with regard to the alternating voltage in the electrical alternating voltage supply network 2, so that the voltage in the direct current circuit 3 can in addition be adjusted over a wide range.
As an alternative to the exemplary embodiments according to FIG. 1 and FIG. 2 the rectifier 1 in a third exemplary embodiment according to FIG. 3 of the exemplary arc furnace power supply device has a series circuit consisting of two passive non-controllable unidirectional power semiconductor switches S7, S8 for each phase R, S, T of the electrical alternating voltage supply network 2. Each of the passive non-controllable unidirectional power semiconductor switches S7, S8 can be formed by a diode. The rectifier 1 implemented according to FIG. 3 represents an extremely robust solution since no kind of control or regulation task exists with regard to the power semiconductor switches S7, S8. If the voltage and current in the direct voltage current 3 are to be adjustable, then optionally according to FIG. 3 an adjuster unit 7 of the rectifier 1 can additionally be provided for the adjustment of the current and voltage in the direct voltage circuit 3, as is shown in an exemplary manner in FIG. 3. If no such adjuster unit 7 is provided, then the series circuits of each of the two passive non-controllable unidirectional power semiconductor switches S7, S8 are connected in parallel and are then moreover connected in parallel with the direct voltage circuit 3.
It should be mentioned that the advantageous rectangular alternating voltage for the arc electrode 4 can also be implemented by means of a matrix inverter that can be connected with the electrical alternating voltage supply network 2.
Advantageously the previous arc furnace power supply device described in detail by means of FIG. 1 to FIG. 4 can find application in an arc furnace.
It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.
REFERENCE SYMBOL LIST
1 Rectifier
2 Electrical alternating voltage supply network
3 Direct voltage circuit
4 Inverter
5 Arc electrode
6 Inverter branch pair
7 Adjuster unit
- S1, S2 Controllable bidirectional power semiconductor switch
- S3, S4 Controllable unidirectional power semiconductor switch
- S5, S6 Controllable bidirectional power semiconductor switch
- S7, S8 Passive non-controllable unidirectional power semiconductor switch
Patent Application
20070247079
