EP2084940B1 - Reactance ballast device - Google Patents

Description

The invention relates to a Reaktanzvorschalteinrichtung for an electric arc furnace, in particular for adjusting the Zusatzreaktanz a transformer of the arc furnace.

An arc furnace, as used for example for steel smelting, is usually preceded by a transformer which adjusts an alternating voltage required for the arc. Since very high power is consumed by an electric arc furnace and high alternating voltages must be transmitted by the upstream transformers, such transformers are usually incorporated in an insulating means in order to avoid flashovers.

An important parameter in AC and AC is the reactance, i. the reactance of a conductor, for example in a current-carrying coil.

For different operating conditions of an electric arc furnace, it is desirable to be able to set different reactances. For this it is for example from the US 1,839,148 A known to integrate in the upstream transformer, a device for Reaktanzeinstellung with a choke coil and with an on-load tap-changer. Typically, such devices are incorporated with the coils and the active part of the transformer in an insulator filled with boiler.

For an electric arc furnace without an additional reactor installed in the transformer tank, it is further known to use air throttle coils set up as additional reactance outside the transformer, for example in an outdoor switchgear.

However, it is not possible to set an optimal reactance under load for all operating conditions of the arc furnace with additional reactances carried out in this way.

Therefore, many arc furnace plants are operated in practice with a fixed preselected reactance. The inductor used for this purpose has at least one tap, which taps the current flowing through the coil after a certain number of turns and thus assigns a defined reactance set to the transformer. To assign the desired reactance, the tap is hardwired. However, a change must be made if it is recognized after a long period of operation that the selected pre-reactance in load operation, i. in furnace operation, is not optimally set, which for example leads to an unnecessary increase in energy consumption, or that the reactance should be adjusted process-dependent. For this purpose, disadvantageously a shutdown of the power supply, thus shutting down the furnace system and the wiring of the transformer with another tap on the choke coil required.

A first object of the invention is to provide a device with which the particular upstream of a transformer reactance is easily adjustable.

A second object of the invention is to provide a transformer with which the reactance is adjusted as accurately as possible.

A third object of the invention is to provide an electric arc furnace, in particular for steel smelting, which is supplied optimally and economically with energy during load operation.

The first object is achieved in that a reactance ballast is specified, in particular for an electric arc furnace, with a choke coil and with a freestanding on-load tap-changer, wherein the on-load tap-changer designed and set to adjust the reactance of the choke coil under load.

The inventive combination of a choke coil with a freestanding on-load tap-changer makes it possible to adjust the pre-reactance under load, so that the optimal pre- or additional reactance can always be selected according to the operational requirements, in particular in application to the load operation of an electric arc furnace.

The reactance ballast is not limited to its use for adjusting the reactance for an electric arc furnace or for an arc furnace transformer. It can also be connected upstream of other energy consumers or plants whose characteristics are determined in particular by the reactance.

Advantageously, a freestanding dry-insulated air throttle coil is selected for the Reaktanzvorschalteinrichtung. In dry-insulated air throttle coils, no insulating oils are used, which reduces general maintenance and fire risk and thus increases efficiency and environmental friendliness.

Furthermore, the choke coil has a suitable number of tapping points, each of which is assigned a number of turns of the coil. Since the inductance, and hence the impedance of a coil, depends on the number of turns that a coil current passes through, by tapping off an alternating current passing through the coil at one tap, the coil impedance, and hence the reactance, i.e., the inductance. the reactance at AC, according to the gradations of the taps are given graded.

In a preferred refinement of the reactance ballast, the free-standing on-load tap-changer combined with the choke coil has a number of input contacts, at least one output contact and a switching element. In this case, the switching element for alternately variable connection of at least one input contact is set up with an output contact. With multiple input contacts, the switching element can thus each connect one or more input contacts to an output contact, depending on the configuration. The respective setting of the switching element thus controls the output on or at an output contact. The on-load tap-changer further comprises a container with an insulating means, in which is designed and arranged for receiving the switching element. The insulating means a sparkover is avoided by high voltages. Due to the insulating properties of the insulating the spark gap is reduced, so that the overall size is reduced.

The switching element suitably has a number of inputs and at least one output, wherein one or each output is associated with a branching node, at least two branches of a bridge circuit converge, the branches are each deactivatable at switching points, the branches each variable with the inputs are connectable, and in pairs with each other via a cross connection to a load switching point are connected, in particular with a vacuum switch.

At the branch node associated with an output of the switching element, the branches belonging to a bridge circuit converge, wherein a bridge circuit comprises at least two branches. The branches make contact with the inputs of the switching element, and can be contacted individually with different inputs, so that several branches abut an input, or only one branch in each case an input. In particular, the variable contacting can be achieved by shifting the branches between different inputs. If all branches are at an entrance or all branches are contacted with this entrance, then a step position is given. If, on the other hand, two branches are resting against two different entrances, then a bridge position is created Are defined. With only two branches, there is only one step position and one bridge position. Such a trained switching element allows switching under load, wherein the switching takes place from one step position to another successively via the formation of bridge positions.

The branches of the bridge circuit of the switching element are connected in pairs with cross-connections, which can be deactivated via a respective load switching point. Between the branching node and the cross connections, the branches are in turn provided with switching points. If switching points on individual branches are now deactivated, for example to move these branches from one to another, the cross-connections connected to these branches initially take over the load and can also compensate for current and voltage fluctuations in the area of the branching node and overload there Prevent switching. Now the cross connections at the load switch points can be deactivated and the branches thus decoupled from the current flow can be shifted. The load switching points are preferably given by vacuum switch, since vacuum switch as a load switch by the shielding effect of the vacuum function reliably and are wear. In addition, the branches between the cross connections and the input-side contact points are suitably provided with throttle elements which ensure a substantially uniform load distribution in the circuit in a bridge configuration.

A desired embodiment of the Reaktanzvorschalteinrichtung is designed to the effect that the number of tap locations of the choke coil coincides with the number of input contacts of the on-load tap-changer and each one tap point is connected to an input contact. In this case, the assignment of the tapping points to the input contacts is preferably linear, so that a counting of the input contacts in a predetermined sequence corresponds to the increasing or decreasing reactance of the choke coil. It exists hereby a desired unique association between the reactance stages and the input contacts.

Furthermore, there is expediently a clear association between the input and output contacts of the on-load tap-changer and the inputs and outputs of the switching element. Thus, in particular, the inputs of the switching element are clearly assigned to the reactance stages. With the switching element as part of the on-load tap-changer, a reactance pre-adjustment of the transformer via the tap selection of the tapping points of the choke coil is thus shown.

The second object is achieved by a transformer, in particular for an electric arc furnace, which is preceded by a Reaktanzvorschalteinrichtung according to the aforementioned type.

The third object is achieved by an electric arc furnace, in particular for the steel smelting, which is preceded by a transformer of the aforementioned type.

FIG 1

eine Reaktanzvorschalteinrichtung mit einer Luftdrosselspule und einem Laststufenschalter,

FIG 2

den Schaltprozess eines Schaltelementes zwischen einer Stufen- und einer Brückenposition in 6 Einzelbildern A bis F, und

FIG 3

als Einlinienschema einen Lichtbogenofen mit einem Transformator und einer Reaktanzvorschalteinrichtung der eingangs genannten Art.

In the following an embodiment of the invention will be explained in more detail with reference to a drawing. In each case show in a schematic representation

FIG. 1

a Reaktanzvorschalteinrichtung with an air throttle coil and an on-load tap-changer,

FIG. 2

the switching process of a switching element between a step and a bridge position in 6 frames A to F, and

FIG. 3

as a single-line diagram of an electric arc furnace with a transformer and a Reaktanzvorschalteinrichtung of the aforementioned type.

In FIG. 1 is a Reaktanzvorschalteinrichtung V with an air throttle coil 1 and a freestanding on-load tap-changer 2 shown in entirety. The air throttle coil 1 is connected via the feed point 3 to a power grid and is provided with a number of uniformly distributed tapping points 4, via which the current passing through the air throttle coil 1 can each be tapped after a multiple of an equal section of the bobbin. Optionally, the air throttle coil 1 is introduced into a container 5, which is shown here by dashed lines.

The freestanding on-load tap-changer 2 has a steel housing 6, the interior 7 of which is filled with an insulating agent, in particular oil. The on-load tap-changer 2 is provided with a number of input contacts 8, which are wired to the tapping points 4 of the air throttle coil 1. In the interior 7 of the steel housing 6, the input contacts 8 represent inputs for a localized there switching element 9, which is here as a whole variably displaceable. The output of the switching element 9 is passed through an output contact 10 to the outside and connected via a power line 11 to a transformer of an electric arc furnace. By a defined displacement of the switching element 9 to a specific input contact 8 and the corresponding tapping point 4, the load circuit of the Reaktanzvorschalteinrichtung V between the feed point 3 and the output line 11 is closed. Thus, the tapping point 4 associated reactance 4 of the air throttle coil 1 is provided on the output line 11.

In FIG. 2 the switching process of a switching element 9 after FIG. 1 between a step and a bridge position in the switching phases A to F shown schematically. Based on the figure for switching phase A, the components of the switching element 9 are first explained in detail, which are given analogously for the remaining switching phases B to F. For the sake of clarity, in the figures for the switching phases B to F the components of the switching element 9 only provided there with reference numerals, where it is necessary for the explanation of the switching process.

This in FIG. 2 illustrated switching element 9 is connected via the on-load tap-changer 2 with the tapping points 4 of the air throttle coil 1, as it is made FIG. 1 is apparent. There are two inputs 121, 12r of the switching element 9 shown in FIG FIG. 1 associated with the input contacts 8 of the on-load tap-changer 2. In the illustration, the switching element 9 has a left line branch or branch 131 and a right line branch 13r, which are each provided with choke coils 141, 14r, and are each connected via contact points 151, 15r with toggle switches 161, 16r to a branching node 17 , The junction node 17 leads to the output 21 of the switching element 9. In each case between the inductors 141, 14r and the contact points 151, 15r there is a cross connection 18 with a vacuum switch 20 between the line branches 131 and 13r, which are connected at the connection points 191 and 19r respectively are. The arrows S indicate the inverse current direction.

A

Das Schaltelement 9 befindet sich in Stufenposition am Eingang 121. Beide Äste 131 und 13r liegen am Eingang 121. Die Kippschalter 161 und 16r sind an den jeweiligen Kontaktstellen 151 und 15r in geschlossener Position, so dass die beiden Äste 131 und 13r unter Last stehen. Die Drosselspulen 141 und 14r gewährleisten eine symmetrische Lastverteilung auf den Ästen 131 und 13r.

B

Der Kippschalter 16r wird geöffnet, an der Kontaktstelle 15r ist der Kontakt gekappt. Dadurch steht nun die Querverbindung 18 über den geschlossenen Vakuumschalter 20 unter Last.

C

Der Vakuumschalter 20 wird unterbrochen, der Ast 13r ist lastfrei und kann verschoben werden, die Gesamtlast liegt auf dem Ast 131.

D

Der lastfreie Ast 13r wird vom Eingang 121 auf den Eingang 12r verschoben.

E

Der Vakuumschalter 20 wird geschlossen, die Querverbindung 18 und der Ast 13r stehen wieder unter Last, die Brückenposition ist aktiv, da jetzt zugleich die Eingänge 121 und 12r über den Verzweigungspunkt 17 einen geschlossenen Kreislauf herstellen.

F

Der Kippschalter 16r wird wieder geschlossen, an der Kontaktstelle 15r ist der Kontakt wieder hergestellt. Statt über die Querverbindung 18 ist die Brückenposition über beide Kontaktstellen 151 und 15r realisiert.

The switching process can be seen from the individual switching phases A to F:

A

The switching element 9 is in step position at the input 121. Both branches 131 and 13r are located at the input 121. The toggle switches 161 and 16r are in closed position at the respective contact points 151 and 15r, so that the two branches 131 and 13r are under load. The choke coils 141 and 14r ensure a symmetrical load distribution on the branches 131 and 13r.

B

The toggle switch 16r is opened, at the contact point 15r the contact is cut off. As a result, the cross connection 18 is now under load via the closed vacuum switch 20.

C

The vacuum switch 20 is interrupted, the branch 13r is load-free and can be moved, the total load is on the branch 131st

D

The load-free branch 13r is shifted from the input 121 to the input 12r.

e

The vacuum switch 20 is closed, the cross-connection 18 and the branch 13r are again under load, the bridge position is active, since now at the same time the inputs 121 and 12r establish a closed circuit via the branch point 17.

F

The toggle switch 16r is closed again, at the contact point 15r the contact is restored. Instead of the transverse connection 18, the bridge position is realized via both contact points 151 and 15r.

In an inverse sequence to the sequence A to F and mirror-symmetric to this branch of 131 can now be moved to produce a step position of both branches 131, 13r on ice drift 12r.

In this way, with the bridge circuit of the switching element 9 via the formation of bridge positions at different inputs, the shift from stage position to stage position between these various inputs under load possible.

FIG. 3 shows an arc furnace 0 with a furnace transformer T and a reactance ballast V of the type mentioned with a choke coil 1 and an on-load tap 2.

Claims (9)

1. Reactance ballast device (V), in particular for an arc furnace, with an induction coil (1) and with a free-standing on-load tap changer (2), the on-load tap changer (2) being formed and designed to set the reactance of the induction coil (1) on load.
2. Reactance ballast device (V) according to Claim 1, the induction coil (1) being in the form of a free-standing dry-insulated air-core induction coil.
3. Reactance ballast device (V) according to Claim 1 or 2, the induction coil (1) being provided with a number of tapping points (4), each of which has an assigned turns number of the induction coil (1).
4. Reactance ballast device (V) according to one of Claims 1 to 3, the on-load tap changer (2) comprising a number of input contacts (8), at least one output contact (10) and a switching element (9), which switching element (9) is designed in each case to connect at least one input contact (4) to an output contact (10), and a container (6) with an insulating material, which container (6) is formed and designed to accommodate the switching element (9).
5. Reactance ballast device (V) according to Claim 4, the switching element (9) having a number of inputs (121, 12r) and at least one output (21), one or each output having an assigned branching node (17), at which at least two branches (131, 13r) of a bridge circuit converge, the branches (131, 13r) in each case being capable of being deactivated at switching points (151, 15r), the branches (131, 13r) in each case being capable of being connected variably to the inputs (121, 12r), and in each case being connected in pairs to a load switching point (20), in particular to a vacuum interrupter, via a cross connection (18).
6. Reactance ballast device (V) according to Claim 3 and according to either of Claims 4 and 5, the number of tapping points (4) of the induction coil (1) corresponding to the number of input contacts (8) of the on-load tap changer (2) and in each case one tapping point (4) being connected to an input contact (8).
7. Reactance ballast device (V) according to Claim 6, the input (8) and the output contacts (10) of the on-load tap changer being uniquely assigned to the inputs (121, 12r) and outputs (A) of the switching element, respectively.
8. Transformer (T), in particular for an arc furnace (0), with a reactance ballast device (V) according to one of the preceding claims for presetting the reactance connected upstream of said transformer.
9. Arc furnace (0), in particular for melting steel, with a transformer (T) according to Claim 8 connected upstream of said arc furnace.

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