EP0040395A2 - Electric power supplying device for electrically heating molten material - Google Patents

Abstract

A system for generating in-phase alternating current components which are fed into a medium held in a melting trough and flow in the medium between electrodes and counterelectrodes immersed in the medium to effect resistance heating. One embodiment of the system includes a supply voltage source, and a plurality of transformers each having a primary winding and a secondary winding, with the primary windings being connected together in series and to the source, each secondary winding being connected between a respective electrode and counterelectrode to provide a respective alternating current component, and each winding having a number of turns corresponding to the desired relative amplitudes of the current components. A second embodiment of the system includes a supply voltage source, at least one input transformer having a primary winding connected to the source and at least one secondary winding, and a plurality of additional transformers each having a primary winding and a secondary winding, with the primary windings of the additional transformers being connected together in series and in a closed loop, each secondary winding of the input transformer being connected in series with at least one secondary winding of the additional transformers between a respective electrode and counterelectrode to provide a respective alternating current component, and each winding of the additional transformers having a number of turns corresponding to the desired relative amplitudes of the current components.

Description

The invention relates to a power supply device for the electrical heating of a molten medium (melt), which is located in a melting tank, by in-phase partial alternating currents which are fed into the melt via one or a number of individual transformers and with one or a number of secondary windings thereof which penetrate the melt via electrodes and counter electrodes immersed in it.

Such power supplies are procedurally used to heat the molten media of this kind, which oppose a resistor to the _'heating power, and therefore constitute a resistive load. Devices in question are used, for example, for glass melts and salt melts.

The heating current from an alternating current source is supplied to the molten medium placed in a melting tank via a transformer or a number of individual transformers with a number of secondary windings and further via electrodes which are immersed in the medium and is removed from the medium via counter electrodes which are likewise immersed dissipated. With the electrode arrangement, the heating current is caused to change into a number Sel streams corresponding to the number of pairs of electrodes and counter electrodes is distributed over a cross section through the molten medium.

The power supply devices used require that the electrodes and the counterelectrodes experience the same current loads as possible, so that they are removed evenly during operation, and consequently all the electrodes involved achieve as long a service life as possible.

But required the same possible power load on the electrodes face opposite difficulties, given the fact that the distribution of the partial alternating currents (power distribution) as a result of differences and Su _- ments of local states is different in a melt and is varied. When power supply devices are used, the partial alternating currents are galvanically separated from one another, are fed from a secondary winding of a transformer (mentioned above), or are fed in via individual transformers. In these devices, a static AC power controller has also been connected upstream of each individual transformer, whereby the partial AC currents can be set individually, but the effort and, with regulation, the difficulty due to the mutual influence of the individual currents and current paths becomes considerable.

Finally, only electrodes and counterelectrodes that are mutually offset in pairs have been connected to a secondary winding of a transformer with a common primary winding or a single transformer, whereby several current paths or current paths of two partial currents can cross each other, so that differences between the partial alternating currents, that can be locally caused in the melt can be reduced. All of the measures described above, which have been taken to ensure that the current load on the electrodes is as equal as possible, are not yet sufficient for this.

It is therefore the object of the invention to provide a power supply device of the type specified in the introduction, in which the electrodes mentioned all experience an equally high current load in a simple manner, in which the partial alternating currents are in a desired size ratio to one another, if a certain temperature distribution should be set in the melt.

According to the invention the object is achieved in such a., Power supply device in that the transformers of the power supply device have the features characterized in claim 1, which consist in that their primary windings are connected in series to a supply voltage and these primary windings and the associated secondary windings each have the same or predetermined number of turns that result in partial alternating currents of the same size or in a desired size / ratio.

In transformers according to the marking according to claim 1 flows through the primary windings (and only one) alternating current of a certain size. As a result, partial alternating currents are forced in the secondary windings, all of which are of the same size in accordance with the number of turns ratios of the primary windings and the secondary windings of the transformers which are to be selected to be of the same size. The voltages on the secondary windings can be of different magnitudes, corresponding to the resistances of the areas of the molten medium through which the individual secondary currents flow.

The same effects with the result that in turn all electrodes and counter-electrodes involved in the heating operation experience an equal current load can also be achieved with a power supply device which has a conventional transformer according to the prior art set out above with a primary winding and a number of secondary windings coupled to it Contains individual transformers, in which, in accordance with a solution alternative that can be derived from the inventive idea according to claim 1, one or more secondary windings of an additional transformer are connected in pure form with one secondary winding of the conventional transformer or the individual transformers, and the primary windings of the additional transformers in .Series connection are short-circuited, these primary windings and the associated secondary windings each have the same number of turns or predetermined numbers of turns that equal gr partial or alternating currents in the desired size ratio.

If, in this device, the secondary windings of the conventional transformer are loaded by different partial alternating currents, the voltages on these secondary windings then being of the same magnitude, then voltages of different magnitudes arise on the secondary windings of the additional transformers, which correspond to the partial alternating currents, and also with different polarities in that the primary partial windings are short-circuited in series. These voltages are combined with the voltages on the secondary windings of the conventional transformer to form total voltages, under which all partial alternating currents become equal.

According to patent claims 1 and 2, there is a common inventive idea that a number corresponds to the desired number of partial flows of a heating flow passing through a molten medium Transformers is connected in such a way that the desired number of partial currents which are as large as possible or have a predetermined ratio is predetermined on the secondary side by a current flowing through the series-connected primary windings.

If the partial alternating currents are to be kept constant, it is sufficient to keep the current flowing through the primary windings constant and, in accordance with a further embodiment of the invention, to arrange the primary windings with an AC actuator with two thyristors connected in parallel in opposite polarity, which is used to keep the primary windings constant supplied AC interacts trained controller.

The transformers designed according to the invention have the properties of a current transformer, so that malfunctions in operation, such as in particular dangerously high overvoltages, which occur when a partial alternating current is interrupted on the secondary side, must be avoided as far as possible.

A second further embodiment of the invention, therefore, it corresponds to that of each secondary winding of the transformers is sungsglied connected in parallel as a protection measure, a bipolar-acting SPDs in series with a Stromerfas- _', and that the outputs of the current detecting members are connected to a common signal line to a Fault evaluator influencing the current controller is guided.

The advantages of the invention are obvious and are characterized in that, with little changes per se in the circuit design and implementation of the transformers, considerable effects are achieved in a power supply device according to the prior art.

• Figur 1 eine Stromversorgungseinrichtung mit Transformatoren gemäß der Erfindung zur Beheizung einer Glasschmelze durch gebündelte Teilwechselströme, die konstantgehalten sind;
• Figur 2 eine Stromversorgungseinrichtung zur Beheizung einer Glasschmelze wie Fig.1, bei der ein Transformator nach dem Stand der Technik und solche gemäß der Erfindung verwendet sind;
• Figur 3 eine Stromversorgungseinrichtung wie in Fig.1, bei der die Transformatoren gemäß der Erfindung eine oder zwei Sekundärwicklungen haben.

Two exemplary embodiments of the invention are described below with reference to the drawing. It shows

• 1 shows a power supply device with transformers according to the invention for heating a glass melt by bundled partial alternating currents, which are kept constant;
• Figure 2 shows a power supply device for heating a glass melt like Figure 1, in which a transformer according to the prior art and those according to the invention are used;
• Figure 3 shows a power supply device as in Figure 1, in which the transformers according to the invention have one or two secondary windings.

In the figures, the same elements are provided with the same reference symbols.

In the devices according to Fig.1 and Fig.2 is a molten glass to be heated in a melting tank W, which is shown in plan view (plan view). Four rod-shaped electrodes, which consist, for example, of graphite, are arranged in a row along two opposing walls of the tub and are immersed in the glass melt. In the row above the electrodes E1 to E4 and in the row below the Ge ^g enelek- trodes e'l to E'4 arranged. All electrodes follow one another in their rows at equal distances, and each electrode E1, E2, E3, E4 is matched by an associated counter electrode E'l, E'2, E'3, E'4 with the same distance. There are four pairs of electrodes (E1, E'1), (E2, E'2), (E3, E'3), (E4, E'4), namely one electrode E and one counter electrode E ', which in the row of which is arranged offset, connected via two power lines to windings, from which four in-phase partial changes currents i _{1 '} i ₂ , i _3' i ₄ are fed into the glass melt for heating. Each partial flow is composed of current paths which, as indicated in FIGS. 1 and 2, diverge from the inlet electrodes E in a belly shape and converge towards the counter electrodes E '. When passing through the glass melt, the partial flows i ₁ and i ₂ and the partial flows i ₃ and i ₄ intersect. Such an arrangement can be expedient in order to achieve the most favorable operating conditions depending on the shape of the tub W and the melting process.

Now it is important that regardless of the local conditions in the glass melt and the resulting electrical resistance in the different volume ranges, the partial alternating currents i ₁ to i ₄ fed in via the electrodes mentioned can be set to the same size and are also kept constant during heating operation, so that all electrodes and counter electrodes constantly experience the same current load. This requirement is met using power supply transformers which are connected in accordance with FIG. 1. According to the number (4) of the secondary currents to be delivered on the secondary side, four transformers 1, 2, 3, 4 are used, each of which has its own transformer core, a primary winding U ₁ , U2 ₁ U ₃ , U ₄ and a secondary winding V ₁ , V ₂ , V ₃ , V ₄ contains. The four primary windings have the same number of turns and are connected in series. On the other hand, the four secondary windings are galvanically separated from each other. They also have the same number of turns, which are determined in a selected ratio to the number of turns of the four primary windings. As explained above and shown in FIG. 1, the four pairs of electrodes immersed in the glass melt are connected to these secondary windings. There are therefore four partial circuits with four ohmic resistances, which are given by the state of the melt in the relevant volume ranges.

If the series connection of the primary windings is now connected to an AC power source, for example to the AC network, the series connection of the four primary windings takes up a primary current, the magnitude of which depends on the line voltage u _N. The secondary windings are therefore loaded with partial currents i ₁ to i _{4 of the} same size if, as assumed above, the ratio of the number of turns of the primary windings and the secondary windings is the same for all windings. The secondary currents are no longer dependent on the resistance of the glass melt, but the voltage distribution across the four primary windings is influenced by the resistance.

You only need to keep the primary current constant so that the secondary currents are constant over time and independent of the mains voltage. This is done according to FIG. 1 with the help of an alternating current actuator 2 ', consisting of two counter-parallel thyristors 21', 22 ', which cooperates with a current regulator 3'.

The requirement for four equal partial alternating currents i ₁ to i ₄ is also used in a power supply device with a conventional transformer 1 'satisfied if DIE _s em according to Figure 2 with each secondary winding V' _1, V _'2, V' _3, V ' ₄ each has an additional secondary winding V ₁ , V ₂ , V ₃ , V ₄ of transformers 1, 2, 3, 4, as described above, is connected in series.

Thus, the four pairs of electrodes (E ₁ , E ' ₁ ), ₍ E2, E'2), (E ₃ , E' ₃ ), ( ^E ₄ , ^E ' ₄ ) are each connected to two secondary windings of transformers connected in series. Furthermore, the transformers 1, 2, 3, 4 must be short-circuited on the primary side, ie the series connection of the four primary sub-windings U ₁ , U _{2 '} U ₃ , U _{4 must} be short-circuited.

If the primary winding U 'of the transformer 1' is now connected to the alternating current source (network N), the primary winding U 'absorbs a primary current which is the sum of the four partial currents i ₁ to 1 ₄ in the four secondary windings V' ₁ to V ₄ corresponds, these partial currents depending on the electrical resistance of the current paths in the glass melt in the individual volume regions per se being of different sizes. Since each partial current flows through a secondary winding of the transformers 1 to 4 short-circuited on the primary side, different voltages, which correspond to the different partial currents in the secondary windings V ₁ to V ₄ , are induced on the primary partial windings, which voltages (at least one of them in relation to the other voltages) have different amounts and polarities, since the sum of the induced voltages is zero at the short-circuited series connection of the primary windings. This has the effect that one of the voltages generated on the additional secondary windings V ₁ to V ₄ is added to or removed from the equal voltages on the secondary windings V ' ₁ to Y' ₄ , so that all four partial alternating currents i ₁ to 1 ₄ can be set to the same size. The circuit arrangement of the transformers 1 to 4 in the device according to FIG. 2 also has the effect that the partial alternating currents are set to the same size even when the voltage of the network N changes. However, if partial currents that remain constant over time are required, then only an alternating current actuator with a constant current regulator according to FIG. 1 is sufficient, which is arranged upstream of the primary winding U 'of 1'.

With regard to the requirement to be able to set the partial alternating currents with a desired small deviation given a fixed ratio of the number of turns of the primary windings and the secondary windings of the transformers 1 to 4, Transfor Mator kernels with a small magnetization requirement, for example cutting tape cores with grain-oriented material sheet.

The example of the transformer circuit according to FIG. 1 shows how and by which means this circuit is protected against overvoltages which can occur as a result of operational disturbances, such as interruption of partial alternating currents. Each secondary winding V ₁ ... V ₄ is a bipolar overvoltage limiter B, known under the name "U diode" or "Thyrector", connected in parallel with a current detection element SE. Each detection element has an output. The outputs of all detection elements are connected to a common signal line, a collecting line 1, as a result of which the current detection elements SE are connected to a fault evaluator S, namely to its input. Each overvoltage that arises on a secondary winding as a result of a fault is signaled by a current pulse, detected by a detection element SE and registered by the fault evaluator S. An output of S is connected to the current regulator 3 'mentioned above. In the event of a fault, the current controller is influenced by S so that, for example, all partial alternating currents are switched off immediately.

The supply of equal-sized partial alternating currents in the glass melt via electrodes and counterelectrodes combined in groups is achieved using power supply transformers which are connected according to FIG. 1, but in which two or more secondary windings are assigned to the primary windings. 3, for example, only two such transformers 1, 2 are used in which the secondary windings U ₁ , U ₂ each have two secondary windings, namely V ₁₁ , V ₁₂ (to U ₁ ) and ^V ₂₁₁ V ₂₂ (to U ₂ ) are assigned. The partial alternating currents i ₁ , i ₂ , i ₃ , i _{4 are} generated from the two of the four secondary windings in the glass melt Group of electrodes E ₁₁ , E _'11 ; E ₁₂ , E _'12 and a group of counter electrodes E ₂₁₁ E'₂₁; E22, E _'22 fed. These two groups can be immersed in two volume regions of the glass melt, which on average differ considerably in terms of their ohmic resistance. Nevertheless, the four currents i ₁ to i _{4 are} equal in size.

However, the application of the invention is not restricted to the embodiments described above with reference to FIGS. 1 to 3, nor is it generally restricted to the effect that the partial alternating currents are all set to the same size. Using the invention, these flows can, if necessary, also be set to different sizes in certain volume ranges of the melt. This can e.g. simply by a correspondingly different determination of the number of turns in the individual transformers connected according to FIG. 1, assigned to the volume regions, in order to achieve that in a glass melt which is located in an elongated trough, the partial flows in the two end regions of the melt are greater than are set in the middle range.

Claims (6)

1. Power supply device for the electrical heating of a molten medium (melt), which is located in a melting tank, by in-phase partial alternating currents, which are fed into the melt via one or a number of individual transformers with one or a number of secondary windings, and which the melt passes through Enforce electrodes and counter electrodes immersed in them, characterized by transformers (1 - 4) in which the primary windings (U ₁ ... U ₄ ) are connected in series to a supply voltage and these primary windings and the associated secondary windings (V ₁ ... V ₄ ) each have the same number of turns or a number of turns such that partial alternating currents (i ₁ ... i ₄ ) of the same size or in a desired size ratio result. 2. Power supply device for heating a molten medium (melt), which is located in a melting tank, by in-phase partial alternating currents, which are fed into the melt via a transformer (1 ') or individual transformers with a primary winding and with one or more secondary windings thereof which penetrate the melt through electrodes and counter electrodes immersed therein, characterized in that with one secondary winding (V'1 ... V'4) of the transformer (1 ') or of the individual transformers, one or more secondary windings (V ₁ ... V ₄ ) an additional transformer (1 - 4) are connected in series, and the primary windings (U ₁ ... U ₄ ) of the additional transformers are short-circuited, these primary windings and the associated secondary windings (V ₁ ... V ₄ ) each have the same number of turns or those specified in such a way that the same size or result in partial alternating currents in a desired size ratio (i ₁ ... i ₄ ). 3. Power supply device according to claim 1 or 2, characterized in that with each transformer (1 ... 4) the primary windings (U ₁ ... U ₄ ) is assigned a secondary winding (V ₁ ... V ₄ ). 4. Power supply device according to claim 1 or 2, characterized in that in each transformer (1 ... 4) the primary windings (U ₁ ... U ₄ ) several secondary ^windings (V ₁₁ , ^V ₁₂ ^{; V} ₂₁ , ^V _22nd ) assigned. 5. Power supply device according to claim 1, characterized in that the primary windings (U ₁ ... U ₄ ) of the transformers (1 ... 4) an AC actuator (2 ') with two oppositely connected parallel thyristors (21', 22 ' ) is arranged upstream, which interacts with a controller (3 ') designed to keep the alternating current (i) supplied to the primary windings constant. 6. Power supply device according to claim 1 and 5, characterized in that each secondary winding (V ₁ ... V ₄ ) of the transformer (1) has a bipolar overvoltage limiter (B) connected in parallel with a current detection element (SE), and that Outputs of the current detection elements are connected to a common signal line (1) which leads to a fault evaluator (S) influencing the current controller (3 ¹ ).

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