EP0040395B1 - 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, via a transformer or a number of individual transformers, each with a primary winding and with one or a number of secondary windings from the same the melt is fed in and penetrate the melt via electrode and counterelectrodes immersed therein.

Such power supply devices can be used in terms of process technology for heating molten media of a type which oppose the heating current with an ohmic resistance, and thus represent an ohmic consumer. used for glass melts and salt melts. Also known are devices of the type specified with only one transformer by DE-PS 841 489 and with several transformers by DE-OS 26 26 278.

The heating current from an alternating current source is supplied to the molten medium, which is placed in a melting tank, via a transformer or a number of individual transformers with a number of secondary windings or one secondary winding each and further via electrodes which are immersed in the medium, and is supplied via counter electrodes which also are immersed, removed from the medium. The electrode arrangement has the effect that the heating current is distributed into a number of partial alternating currents corresponding to the number of pairs of electrodes and counter-electrodes over a cross section through the molten medium.

The power supply devices are required to achieve uniform heating of the melt material and to subject the electrodes and counter-electrodes to the same current loads as possible, so that they are removed evenly during operation. therefore all electrodes involved should achieve the same service life as possible.

Difficulties oppose the same possible current loading of the electrodes in that the distribution of the partial alternating currents (current distribution) is different due to differences and changes in the local conditions in a melt and is changed. A uniform or a current distribution in a desired ratio is achieved by feeding the partial alternating currents galvanically separated from each other from a secondary winding of a transformer or via individual transformers, and essentially by the fact that the individual electrode pairs are electromagnetically linked to one another by a current distribution circuit (DE-PS 841 489). In the device according to DE-OS 26 26 798, for example, the primary windings of the individual transformers are connected in series to the supply source. The series circuit is a voltage regulator, which is influenced by a current and a voltage detector, which keeps the power supply and the total current and thus the partial currents constant. Differences between the partial alternating currents, which can be caused locally in the melt, are reduced by only connecting electrodes and counter-electrodes, which are spatially offset in pairs, to a secondary winding of a transformer with a common primary winding or a single transformer.

The invention has for its object to provide a power supply device of the type specified, in which an equally high current load is achieved with a current distribution circuit which electromagnetically detects the individual electrode pairs using a conventional transformer with a primary winding, to which the total current is supplied, or-how known-by different transformation ratios of the interlinking transformers, a current load is achieved in which the partial alternating currents are in a desired size ratio to one another if a certain temperature distribution in the melt is to be set.

This claim is achieved according to the invention in that one or more secondary windings of an additional transformer are connected in series with a secondary winding of a transformer or individual transformers, and the primary windings of the additional transformer are short-circuited, these primary windings and the associated secondary windings each individually have the same or predetermined number of turns that result in partial AC currents of the same size or in a desired size ratio.

In this power supply device, a conventional medium-high-power network transformer with a primary winding and a number of secondary windings or individual transformers coupled therewith act as a conventional transformer or transformers, and an additional transformer, several of which are short-circuited in series. These primary windings and the associated secondary windings each have the same or predetermined number of turns that result in partial AC currents of the same size or in the desired size ratio.

With this device, the secondary windings of the conventional transformer are caused by different partial alternating currents loaded, the voltage on these secondary windings then being of the same magnitude, voltages of different magnitudes corresponding to the partial alternating currents and also with different polarity arise on the secondary windings of the additional transformers 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.

Corresponding to the desired number of partial flows of a heating current passing through a molten medium, a number of transformers is switched in such a way that the desired number of partial flows which are as large as possible or have a predetermined ratio is specified on the secondary side by a current flowing through the series windings.

A secondary winding can be assigned to the primary windings of the additional transformer (s), or a plurality of secondary windings can be assigned.

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 alternating current actuator with two oppositely polarized thyristors, 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 interference during 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.

• Fig. 1 eine Stromversorgungseinrichtung gemäß der Erfindung und
• Fig. 2 eine Stromversorgungseinrichtung nach Fig. 1 mit abgeänderter Transformationschaltung.

The essence of the invention is to be explained in more detail with the aid of the exemplary embodiments shown in the figures. Show it:

• Fig. 1 shows a power supply device according to the invention and
• Fig. 2 shows a power supply device according to Fig. 1 with a modified transformation circuit.

The molten glass to be heated is located in the melting tank W, which is shown in plan view (plan view). Four rod-shaped electrodes, for example made of graphite, are arranged in a row along two opposing walls of the tub and are immersed in the glass melt. The electrodes E, to E ₄ are arranged in the row above and the counter electrodes E 'to E' ₄ are arranged in the row below. All electrodes follow one another in the respective row at equal distances, and each electrode E1, E2, E3, E4 is opposed by an associated counter electrode E1 ', E2', E3 ', E4' with the same distance in each case. There are four pairs of electrodes (E1, E'1), (E2, E'2), (E3, E'3), (E4, E'4), one electrode E and one counter electrode E ', each over two power lines connected to windings, from which four in-phase partial alternating currents i ₁ , i ₂ , i ₃ , i ₄ are fed into the glass melt for heating. Each partial current is composed of current paths which - as indicated - diverge from the electrodes E from the belly and converge towards the counterelectrode 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.

So that all electrodes and counterelectrodes now experience the same current load, the partial alternating currents i ₁ to i ₄ fed in via the electrodes must be adjustable to the same size regardless of the local conditions in the molten glass and the resulting electrical resistance in the different volume ranges and, if necessary, during heating operation be kept constant. This requirement is met using a power supply transformer 1 'with a primary winding U', which is connected to an AC network N, four secondary windings V ' ₁ , V' ₂ , V ' ₃ , V' ₄ with an additional transformer system 1 consisting of four individual transformers 1 , 2, 3, 4 each with a primary winding U1 to U4 and a secondary winding V1 to V4. These as the secondary windings V ' ₁ to V' ₄ have the same number of turns of the four primary windings or for the primary winding U 'of 1' are fixed.

You only need to keep the primary current constant so that the secondary currents are constant over time and independent of the mains voltage. An AC power controller can be used for this purpose, consisting of two thyristors connected in parallel, which cooperates with a current regulator.

The requirement for four partial AC currents i ₁ to i _{4 of} equal size is met in the power supply device with the transformer 1 'in that each secondary winding V' ₁ , V ' ₂ , V' ₃ , V ' _{4 has} an additional secondary winding V ₁ , V ₂ , V ₃ , V _{4 of} the transformers 1, 2, 3, 4 is connected in series, with which the four pairs of electrodes (E _i , E ' ₁ ), (E2, E' ₂ ), (E3, E ' ₃ ), (E ₄ , E ' ₄ ) are connected to two secondary windings of transformers connected in series, and that the transformers 1, 2, 3, 4 are short-circuited on the primary side, ie that the series connection of the four primary partial windings U _i , U ₂ , U ₃ , U ₄ is short-circuited in itself.

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 i ₄ in the four secondary windings V' ₁ to V ' ₄ corresponds, with these partial flows depending speed of the electrical resistance of the current paths in the glass melt in the individual volume ranges can be different in itself. Since each partial current flows through a secondary winding of the transformers 1 to 4 short-circuited on the primary side, different voltages corresponding to the different partial currents in the secondary windings V, 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 causes one of the voltages that are generated on the additional secondary windings V to V _{4 to} be added to or removed from the equal voltages on the secondary windings V ' ₁ to V' ₄ , so that all four Partial currents i ₁ to i _{4 can be set to the} same size. The circuit arrangement of the transformers 1 to 4 in this device also has the effect that the partial alternating currents are each 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 an assigned constant current regulator, which is arranged upstream of the primary winding U 'of l', is sufficient.

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

To protect the transformer circuit against overvoltages, at least each secondary winding V ' ₁ ... V' _4, a bipolar overvoltage limiter B, which are known, for example, under the designation "U-diode" or "Thyrector", is connected in parallel with a current detection element. Each detection element has an output. The outputs of all detection elements are connected to a common signal line, as a result of which the current detection elements are connected to a fault evaluator, namely to its input. Every overvoltage that arises on a secondary winding as a result of a fault is signaled by a current pulse, detected by a detection element and registered by the fault evaluator. An output thereof is connected to the current regulator mentioned. In the event of a fault, the current controller is influenced so that, for example, all partial alternating currents are switched off immediately.

Partial alternating currents of the same size are fed into the glass melt via electrodes and counterelectrodes combined in groups using power supply transformers which are connected according to FIG. 2 and in which two or more secondary windings are assigned to the primary windings, and only two transformers 1, 2 be used. The primary windings U ₁ , U ₂ are assigned two secondary windings, namely V ₁₁ , V ₁₂ (to U,) and V ₂₁ , V ₂₂ (to U ₂ ).

The partial alternating currents i ₁ , i ₂ , i ₃ , i _{4 are} generated from the two of the four secondary windings in total in the glass melt via a group of electrodes E ₁₁ , E _'11 , E ₁₂ , E' ₁₂ and a group of counter electrodes E ₂₁ , E _'21 ; E ₂₂ , 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 set} equal.

The partial alternating currents need not be set to the same size. Rather, they can be set to different sizes in certain volume ranges of the melt, if necessary. This can e.g. simply by a correspondingly different definition of the number of turns in the individual transformers assigned to the volume ranges and the number of turns of the assigned secondary windings of a transformer with only one primary winding, in order to achieve that the partial currents in a glass melt which is located in an elongated trough are set larger in the two end regions of the melt than in the middle region.

Claims (4)

1. Current supply equipment for the electrical heating of a molten medium (smelt), which is disposed in a crucible, by in-phase partial alternating currents which are fed through a transformer or through individual transformers with a primary winding and with one or more secondary windings from these into the smelt and pass through the smelt by way of electrodes and counterelectrodes immersed therein, characterised thereby, that one or more secondary windings (V₁ ... V₄) of an additional transformer (1 to 4) are each connected in series with a respective secondary winding (V'₁ ... V'₄) of a transformer (1') or individual transformers and the primary windings (U₁... U₄) of the additional transformers are short-circuited in series connection, these primary windings and the associated secondary windings (V₁... V₄) each have numbers of turns which are equal or predetermined in such a manner that partial alternating currents (i₁ ... i4) result, which are equally great or stand in a desired magnitude ratio.

2. Current supply equipment according to claim 1, characterised thereby, that a secondary winding (V₁ ... V₄) is associated with the primary windings (U₁... U₄) for each transformer (1 ... 4).

3. Current supply equipment according to claim 1, characterised thereby, that several secondary windings (V₁₁, V₁₂; V₂₁, V₂₂) are associated with the primary windings (U₁ ... U₄) for each transformer (1 ...4).

4. Current supply equipment according to claim 1, characterised thereby, that an alternating current member (2') with two oppositely poled, parallel-connected thyristors (21', 22') is arranged in front of the primary winding of the transformer (1') and co-operates with a regulator (3') constructed to keep the alternating current (i) fed to the primary winding (U') constant.

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