EP4224992A1 - Operating method for a an arc furnace - Google Patents

Abstract

Metal (2) located in a furnace body (1) of an electric arc furnace is melted during a melting phase. A control device (9) of the electric arc furnace determines provisional desired voltage values (U1*) on the basis of desired electrical variables (X*) from the electrical energy to be supplied to the electrodes (6). When voltages (U) corresponding to the preliminary voltage setpoints (U1*) are applied to the electrodes (6), first actual electrical variables (X) of electrical energy supplied by the electrodes (6) are brought as close as possible to the electrical setpoint variables (X*). . The control device (9) controls an energy supply device (3) of the arc furnace based on final desired voltage values (U2*). As a result, voltages (U) corresponding to the final desired voltage values (U2*) are applied to the electrodes (6). As a result, the energy supply device (3) draws electrical energy from a supply network (4) and feeds it to the electrodes (6) via a furnace transformer (5). At least during an initial phase of the melting phase, the control device (9) determines the final desired voltage values (U2*) by limiting the provisional desired voltage values (U1*) to a permissible maximum value (Umax). The maximum value (Umax) is below a possible maximum value (U0) that can be applied to the electrodes (6) by the energy supply device (3).

Description

field of technology

• anhand elektrischer Sollgrößen von den Elektroden zuzuführender elektrischer Energie vorläufige Spannungssollwerte ermittelt, so dass bei Anlegen von mit den vorläufigen Spannungssollwerten korrespondierenden Spannungen an die Elektroden erste elektrische Istgrößen von den Elektroden zugeführter elektrischer Energie den elektrischen Sollgrößen so weit wie möglich angenähert werden, und
• eine Energieversorgungseinrichtung des Lichtbogenofens basierend auf endgültigen Spannungssollwerten ansteuert, so dass mit den endgültigen Spannungssollwerten korrespondierende Spannungen an die Elektroden angelegt werden, so dass die Energieversorgungseinrichtung elektrische Energie aus einem Versorgungsnetz bezieht und über einen Ofentransformator den Elektroden zuführt.

The present invention is based on an operating method for an arc furnace, wherein metal located in a furnace vessel of the arc furnace is melted during a melting phase, with a control device of the arc furnace

• Provisional voltage reference values are determined on the basis of electrical reference values from the electrical energy to be supplied to the electrodes, so that when voltages corresponding to the provisional reference voltage values are applied to the electrodes, first electrical actual values of the electrical energy supplied to the electrodes are approximated as closely as possible to the electrical reference values, and
• controls an energy supply device of the arc furnace based on final desired voltage values, so that voltages corresponding to the final desired voltage values are applied to the electrodes, so that the energy supply device obtains electrical energy from a supply network and supplies it to the electrodes via a furnace transformer.

The present invention is also based on a control program for a control device of an arc furnace, the control program comprising machine code which can be processed by the control device, the processing of the machine code by the control device causing the control device to operate the arc furnace in accordance with such an operating method.

The present invention is also based on a control device for an electric arc furnace, the control device is programmed with such a control program so that the control device operates the electric arc furnace according to such an operating method.

• wobei der Lichtbogenofen ein Ofengefäß aufweist, dem Metall zuführbar ist,
• wobei der Lichtbogenofen eine Energieversorgungseinrichtung und Elektroden sowie einen Ofentransformator aufweist,
• wobei die Energieversorgungseinrichtung eingangsseitig mit einem Versorgungsnetz und ausgangsseitig über den Ofentransformator mit den Elektroden verbunden ist,
• wobei der Lichtbogenofen eine Steuereinrichtung aufweist, von der die Energieversorgungseinrichtung ansteuerbar ist,
• wobei die Steuereinrichtung so wie obenstehend erläutert ausgebildet ist.

The present invention is also based on an electric arc furnace

• wherein the arc furnace has a furnace vessel to which metal can be fed,
• wherein the arc furnace has an energy supply device and electrodes as well as a furnace transformer,
• wherein the energy supply device is connected to a supply network on the input side and to the electrodes via the furnace transformer on the output side,
• wherein the arc furnace has a control device, by which the energy supply device can be controlled,
• wherein the control device is designed as explained above.

State of the art

The items mentioned are generally known. For example, on the WO 2015/176 899 A1 to get expelled. Also the EP 1 026 921 A1 and the EP 3 124 903 A1 can be mentioned in this context.

Summary of the Invention

When melting metal - especially steel - in an arc furnace, the electrical energy is supplied to the electrodes of the arc furnace via a furnace transformer. The furnace transformer is often connected to the supply network via a medium-voltage transformer. The furnace transformer provides several voltage levels. For the range of constant power and other high-current ranges, the respective voltage level can be selected on the furnace transformer. Fine control within a specific voltage level can be done, for example, by means of impedance control.

Only a few voltage steps are possible with this procedure, and the electrode currents are subject to strong fluctuations. To reduce the fluctuations, the positioning of the electrodes is controlled mechanically, mostly via hydraulic adjustment devices. The mechanical adjustment of the electrodes shows a significantly lower dynamic than the real behavior of the arcs. The fluctuations can therefore only be adequately compensated. Furthermore, the fluctuations lead to considerable loads on the components, for example the high-current cables, the current-carrying support arms, the hydraulic cylinders, etc. The fluctuations occur both in the melting phase and in a subsequent flat bath phase.

When setting the electrode voltage via the voltage levels of the furnace transformer, the positioning of the electrodes must be continuously readjusted. The readjustment can, for example, take place in such a way that a specific impedance or a specific power is controlled. However, since the dynamics of the positioning device are relatively low compared to the changes in the electrical system of the arc, certain fluctuations remain that cannot be corrected. As a result, the energy input into the molten metal is not optimal.

From the documents of the prior art, in particular from WO 2015/176 899 A1 and the EP 3 124 903 A1 and to a limited extent also from the EP 1 026 921 A1 , Procedures are known in which the electrode voltages can be adjusted continuously. These configurations offer significant advantages over setting the electrode voltage via voltage steps of the furnace transformer. On the one hand, the electrode voltages can be varied not only gradually, but continuously. On the other hand, the furnace transformer can be designed more simply because it does not have to provide several voltage levels. Furthermore, further types of regulation are made possible by these refinements.

If—as is known from the prior art—the electrode voltages can be adjusted continuously, the electrical energy is often supplied with constant power or constant current. The power or the current can be maximum, that is as large as possible due to the design ("energy supply device, deliver what you can"). In this case, the voltages applied to the electrodes are used to set the desired power or the desired current. Especially during the initial phase of a melting phase of the arc furnace, when the electrodes are still quite high up near the cover of the arc furnace, this can result in the arc not forming towards the metal but towards the cover when viewed from the electrodes. This not only leads to a significantly reduced introduction of energy into the metal, but also to significantly increased wear of the cover, up to and including damage to the cover occurring after a short time.

The object of the present invention is to create possibilities by means of which the disadvantages of the prior art can be avoided.

The object is achieved by an operating method with the features of claim 1. Advantageous configurations of the operating method are the subject matter of dependent claims 2 to 5.

According to the invention, an operating method of the type mentioned at the beginning is designed in that the control device determines the final voltage setpoints at least during an initial phase of the melting phase by limiting the provisional voltage setpoints to a permissible maximum value, with the permissible maximum value being below a possible maximum value that can be transmitted from the energy supply device to the Electrodes can be applied.

If, from the point of view of the design of the energy supply device, up to 1200 V can be applied to the electrodes and 5000 A should flow through the electrodes, in the prior art the voltage is regulated to the full 1200 V if necessary in order to achieve the desired set a current of 5000 A. According to the invention, on the other hand, such compensation only takes place up to a value below 1200 V, for example up to a maximum of 700 V. If a voltage value above 700 V is required to set a current of 5000 A, the deviation of the current from the actual desired value (= 5000 A) accepted. Although this means that less energy is supplied to the arc furnace, the energy supplied is reliably introduced into the metal that is to be melted, but not into the components of the arc furnace itself. The numerical values of 700 V and 1200 V as well as 5000 A are given as examples Values used for explanation. In practice, larger or smaller values can also occur. In particular, the current can often be considerably larger.

In the very simplest embodiment, the permissible maximum value is fixed. In this case it is possible that the maximum allowed value is taken into account only during the initial phase of the melting phase, but no longer in a later part of the melting phase. Alternatively, it is possible that the permissible maximum value is taken into account during the entire melting phase, but no longer in the subsequent flat bath phase.

In other implementations, the maximum allowed value can be dynamic.

For example, it is possible for the control device to accept an input value from an operator and for the control device to determine the permissible maximum value as a function of the input value. It is alternatively possible that the input value always determines the permissible maximum value, that is, with an input value of, for example "500 V" the permissible maximum value is always 500 V as well. Alternatively, it is possible that the input value is specified only in terms of an upper limit. In this case, the control device can initially determine the permissible maximum value in a different way. If the value determined in this way is smaller than the voltage value determined by the input value (for example only 450 V compared to 500 V according to the input value), the value determined by the control device (450 V) is used as the permissible maximum value. If the value determined by the control device is greater than the voltage value determined by the input value (for example 550 V), the voltage value determined by the input value (500 V) is used as the permissible maximum value. Here, too, the stated numerical values of 450 V, 500 V and 550 V are purely exemplary values that are used for explanation. In practice, larger or smaller values can also occur.

Alternatively, a specification according to an input value can take place continuously or in stages.

In another embodiment, it is possible for the control device—as an alternative or in addition to considering the input value—to determine the permissible maximum value as a function of a period of time that has elapsed since the beginning of the melting phase. For example, the permissible maximum value can initially have a relatively low value and after a specific waiting time of, for example, 5 minutes has elapsed, it can be increased suddenly, in several steps, or continuously (linearly or non-linearly). The permissible maximum value can be increased up to the possible maximum value (and theoretically even beyond) in later stages, ie after at least the initial phase of the melting phase. In this case, the voltage limitation according to the invention is no longer active from the point in time at which the possible maximum value is reached. The time period of 5 minutes mentioned is also only an example. In practice, larger or smaller values can also occur.

As a rule, the positioning of the electrodes varies over time. The positioning of the electrodes can be known to the control device. For example, the control device can also carry out the positioning of the electrodes or the control device can be supplied with the positioning of the electrodes from the outside. In one embodiment of the present invention, it is therefore possible for the control device to determine the permissible maximum value as a function of the positioning of the electrodes.

Analogously to a determination based on a period of time that has elapsed since the start of the melting phase, the permissible maximum value can initially have a relatively low value when determining based on the positioning of the electrodes, and when certain positions are reached, i.e. as a result in later sections of the melting phase, can be increased in one step, in several steps or continuously (linearly or non-linearly). The allowed maximum value can be increased up to the possible maximum value and even beyond.

In another embodiment of the present invention, it is possible for the control device to determine progress in melting the metal in the arc furnace and the permissible ones by evaluating the time profile of second electrical actual variables of the electrical energy supplied to the electrodes and/or by evaluating acoustic actual variables of the arc furnace Maximum value determined depending on the progress determined.

The term "second actual electrical variables" is used for purely formal differentiation from the first actual electrical variables. It is intended to express that the actual electrical variables, by means of which the control device determines the progress of the melting of the metal in the electric arc furnace, are not necessarily the same actual electrical variables which, if possible, are the desired electrical variables be approximated. This is possible, but not mandatory. For example, the first actual electrical variables can be the electrode currents, while the second actual electrical variables can be the voltages applied to the electrodes or the power flowing through the electrodes. In individual cases, however, the actual electrical variables can also be the same.

Analogously to a determination as a function of a period of time that has elapsed since the beginning of the melting phase, the permissible maximum value can initially have a relatively low value when a determination is made as a function of the determined progress and when a certain process progress is reached in one jump, in several stages or continuously ( linear or non-linear). The permissible maximum value can be increased up to the possible maximum value and also beyond.

The object is also achieved by a control program with the features of claim 6. According to the invention, the processing of the machine code by the control device causes the control device to operate the electric arc furnace in accordance with an operating method according to the invention.

The object is also achieved by a control device with the features of claim 7. According to the invention, the control device is programmed with a control program according to the invention, so that the control device operates the electric arc furnace according to an operating method according to the invention.

The object is also achieved by an electric arc furnace having the features of claim 8. According to the invention, the control device is designed as a control device according to the invention.

Brief description of the drawings

FIG 1

ein Blockschaltbild eines Lichtbogenofens,

FIG 2

ein Ofengefäß während einer Schmelzphase,

FIG 3

ein Ablaufdiagramm,

FIG 4

das Ofengefäß während einer Flachbadphase,

FIG 5

ein Zeitdiagramm,

FIG 6

ein Positionsdiagramm und

FIG 7

ein Phasendiagramm.

The characteristics, features and advantages of this invention described above, and the manner in which they are achieved, will become clearer and more clearly understood in connection with the following description of the exemplary embodiments, which are explained in more detail in connection with the drawings. This shows in a schematic representation:

FIG 1

a block diagram of an electric arc furnace,

FIG 2

a furnace vessel during a melting phase,

3

a flowchart,

FIG 4

the furnace vessel during a flat bath phase,

5

a time chart,

6

a position diagram and

FIG 7

a phase diagram.

Description of the embodiments

According to FIG 1 an arc furnace has a furnace vessel 1 . The furnace vessel 1 can - see FIG 2 - Metal 2 are supplied. The metal 2 is fed to the furnace vessel 1 in a solid state. The metal 2 can be, for example, steel and, in the case of steel, in particular scrap.

The arc furnace also has an energy supply device 3 . The energy supply device 3 is connected to a supply network 4 on the input side. The supply network 4 is usually a medium-voltage network that has a nominal voltage in the 2-digit kV range and is operated at a base frequency f0. The base frequency f0 is usually 50 Hz or 60 Hz. The supply network 4 is as shown in FIG 1 usually a three-phase network.

The arc furnace also has a furnace transformer 5 and electrodes 6 . The power supply device 3 is connected to the electrodes 6 via the furnace transformer 5 on the output side. As a rule, according to the representation in FIG 1 several electrodes 6 available and is still the furnace transformer 5 is designed as a three-phase transformer. However, other configurations are also possible, in particular a single-phase configuration. Irrespective of the specific configuration, however, the electrode voltages U applied to the electrodes 6 are significantly below the nominal voltage of the supply network 4. The electrode voltage U is in FIG 1 only shown for one of the electrodes 6. The electrode voltages U are usually in the range of several 100 V. In individual cases, voltages above 1 kV are also possible. However, 2 kV are generally not exceeded.

As a rule, switching devices are also present, by means of which the energy supply device 3 can be separated from the supply network 4 . Furthermore, switching devices can be present, by means of which the energy supply device 3 can be separated from the furnace transformer 5 and/or the furnace transformer 5 from the electrodes 6. The switching devices perform purely binary switching operations, but no adjustment of voltages and currents. Furthermore, active or passive filter devices can be arranged on the primary or secondary side of the furnace transformer 5 . The switching devices and also the filter devices are of secondary importance for the functioning according to the invention and are therefore FIG 1 (and also the other FIGs) are not shown for the sake of clarity.

The energy supply device 3 can draw electrical energy from the supply network 4 and feed the drawn electrical energy to the electrodes 6 via the furnace transformer 5 . For this purpose, the energy supply device 3 generally has a large number of semiconductor switches. Possible configurations of the energy supply device 3 are in WO 2015/176 899 A1 ("Gold Standard ") described. Alternatively, for example, the configurations according to the EP 3 124 903 A1 or the EP 1 026 921 A1 be used. Regardless of the specific design of the energy supply facility 3, however, the energy supply device 3 is able on the output side--that is, towards the furnace transformer 5--to carry out a quasi-continuous gradation of the electrode voltages U applied to the electrodes 6 and/or the electrode currents I supplied to the electrodes 6. The electrode current I in is analogous to the representation for the electrode voltages U FIG 1 also only shown for one of the electrodes 6 .

The electrode voltages U can have a maximum value U0 (see 5 to 7 ) to reach. The value U0 - ie the possible maximum value of the electrode voltages U - is determined by the nominal voltage of the supply network 4, the design of the energy supply device 3 and the design of the furnace transformer 5. For example, the value U0 can be 1200 V.

Furthermore, the arc furnace has a positioning device 7 . By means of the positioning device 7, the electrodes 6, as in FIG 1 is indicated by a double arrow 8 next to one of the electrodes 6 are positioned. In the simplest case, the electrodes 6 are positioned together. However, the electrodes 6 can also be positioned individually. The direction of movement in which the electrodes 6 are positioned can be vertical. Alternatively, the direction of movement can also be slightly inclined with respect to the vertical. Also in this case, however, the component in the vertical direction is the dominating component of the movement. The positioning device 7 can have, for example, one or more hydraulic cylinder units.

Finally, the arc furnace has a control device 9 . At least the energy supply device 3 is controlled by the control device 9 . The control device 9 thus generates control values A1 with which it controls the energy supply device 3 . According to the control values A1, the energy supply device 3 is operated.

The positioning device 7 is often also controlled by the control device 9 , in this case the control device 9 generates further control values A2 with which it controls the positioning device 7 . In this case, the positioning device 7 is operated in accordance with these control values A2. However, the actuation of the positioning device 7 as such is not the subject of the present invention and is therefore not explained in any more detail.

The control device 9 is designed as a software-programmable control device. this is in FIG 1 indicated by the specification "µP" (for microprocessor-controlled). The mode of action and operation of the control device 9 is determined by a control program 10 with which the control device 9 is programmed. The control program 10 includes machine code 11 which can be processed by the control device 9 . The processing of the machine code 11 by the control device 9 causes the control device 9 to operate the arc furnace according to an operating method, as is explained in more detail below in connection with the other FIGS.

First, the furnace body 1 according to 3 charged with the metal 2 in a step S1. The loading can take place under the control of the control device 9 . However, it does not have to take place under the control of the control device 9 . Step S1 is therefore in 3 shown only as dashed lines.

The charging of the furnace vessel 1 with the metal 2 is followed by a melting phase of the arc furnace. During the melting phase, the metal 2 is melted into a molten metal 12 . The melting phase includes steps S2 to S6. A flat bath phase follows the melting phase. The shallow bath phase includes steps S7 through S11.

In the melting phase, the control device 9 first accepts setpoint values X* in step S2. The setpoint variables X* are electrical variables for electrical energy that are to be supplied to the electrodes 6 . For example, it can be electrical target currents or electrical target powers.

In step S3, the control device 9 determines final desired voltage values U2*. To determine the final desired voltage values U2*, the control device 9 first determines preliminary desired voltage values U1* using the desired electrical values X* (possibly also taking into account first actual electrical values X which are characteristic of the electrical energy supplied to the electrodes 6). Provisional voltage setpoints U1* are determined in such a way that when voltages U corresponding to provisional voltage setpoints U1* are applied to electrodes 6, first electrical actual variables X are approximated to corresponding setpoint variables X* as closely as possible. An attempt is therefore made, for example, to bring the actual electrical current or the actual electrical power as close as possible to the target electrical current or to the target electrical power. However, in step S3, the provisional desired voltage values U1* determined in this way are capped at an upper limit to a permissible maximum value Umax. The permissible maximum value Umax is (see the 5 to 7 ) in turn below the possible maximum value U0. It is usually between 50% and 75% of the possible maximum value U0. With a possible maximum value U0 of 1200 V, the permissible maximum value Umax can be between 600 V and 900 V, for example.

Then, in step S4, the control device 9 determines the control values A1 for the energy supply device 3. The determination is based on the final desired voltage values U2*. In step S5, the control device 9 controls the energy supply device 3 according to the determined control values A1. Due to the corresponding control voltages U corresponding to the final desired voltage values U2* are applied to the electrodes 6. As a result, the energy supply device 3 draws electrical energy from the supply network 4 and feeds the electrical energy to the electrodes 6 via the furnace transformer 5 . As a result, arcs 13 form as a result.

In step S6, the control device 9 checks whether a termination condition has been reached. The termination condition may be that the melting phase as such is terminated. The melting phase is complete when the molten metal 12, as shown in FIG FIG 4 has completely or at least essentially formed a continuous horizontal surface. It is either the metal 2 completely melted or the not yet melted elements of the metal 2 are completely below the surface of the metal melt 12 or the not yet melted elements of the metal 2 protrude only slightly above the surface of the metal melt 12 also. Furthermore, a slag layer 14 may have formed on the surface of the molten metal 12 . Alternatively, the termination condition can be, for example, that an initial phase has been completed within the melting phase, for example a drilling phase. Irrespective of the design of the termination condition, however, the termination condition is generally not met until several minutes after the beginning of the melting phase.

It is possible for the control device 9 to evaluate measured actual variables of the arc furnace as part of the check as to whether the termination condition has been met. For example, it is possible for the control device 9 to evaluate the electrode currents I and/or the electrode voltages U, in particular their fluctuations. The control device 9 can also evaluate acoustic parameters of the arc furnace, for example the noise level or the acoustic spectrum of the noise generated. Alternatively, it is possible for the control device 9 to be controlled by an operator 15 (see FIG 1 ) it is specified that the termination condition has been reached.

If the termination condition has not yet been reached, the controller 9 returns to step S2 (alternatively to step S3). If, on the other hand, the termination condition is reached, the control device 9 goes to step S7 and thus to a further operating phase of the electric arc furnace. The further operating phase can be the flat bath phase, for example. Alternatively, the further operational phase can be a later portion of the melting phase plus the flat bath phase.

In the further operating phase of the arc furnace, the control device 9 receives the setpoint values X* in step S7. Furthermore, the control device 9 determines the final desired voltage values U2* in step S8. Then, in step S9, the control device 9 determines the control values A1 for the energy supply device 3. In step S10, the control device 9 controls the energy supply device 3 according to the determined control values A1.

Steps S7 through S10 essentially correspond to steps S2 through S5. The only difference is that in step S8 the control device 9 accepts the provisional desired voltage values U1* directly as the final desired voltage values U2*, ie it does not limit it to the permissible maximum value Umax.

In step S11, the control device 9 checks whether the further operating phase of the arc furnace has ended. Analogously to the check in step S6, it is possible for the control device 9 to evaluate actual variables of the electric arc furnace that are detected by measurement as part of the check in step S11. Alternatively, it is possible for the control device 9 to be instructed by the operator 15 that the further operating phase has ended.

If the further operating phase has not yet ended, the control device 9 goes back to step S7 (alternatively to step S8). If, on the other hand, the further operating phase has ended, the control device 9 goes to a step S12. In step S12, the molten metal 12 produced is removed from the furnace body 1, for example poured into a ladle (not shown). The molten metal 12 can be removed under the control of the control device 9 . However, it does not have to take place under the control of the control device 9 . Step S12 is therefore in FIG 3- analogous to step S1 - shown only in dashed lines.

It is also possible for steps S6 to S10 to be omitted and instead to go back to step S2 or step S3 from step S11. In this case, the permissible maximum value Umax is taken into account during the entire operation of the arc furnace.

There are various options for determining the permissible maximum value Umax.

For example, the permissible maximum value Umax can be set by the control device 9 in accordance with the illustration in 5 can be determined as a function of time t. In this case, a point in time t1 corresponds to the start of the melting phase, i.e. in principle the first ignition of the arcs 13 after the furnace vessel 1 has been charged with the metal 2. The permissible maximum value Umax generally has its lowest value at the point in time t1. Later, the permissible maximum value Umax - according to the presentation in 5 continuously, alternatively in one or more stages - to a higher value. In particular, it can reach the possible maximum value U0 at a point in time t2. In the case of the design according to 5 the control device 9 thus determines the permissible maximum value Umax as a direct function of a period of time that has elapsed since the start of the melting phase: Is the time period that has elapsed since the start of the melting phase known, the associated currently valid permissible maximum value Umax can also be determined.

Alternatively, the permissible maximum value Umax can be set by the control device 9 as shown in 6 can be determined as a function of the positioning p of the electrodes 6. The representation in 6 is such that the positioning p corresponds to the distance between the undersides of the electrodes 6 and a cover 15 of the furnace vessel 1 . As a rule, the permissible maximum value Umax has its lowest value at the smallest positioning p (ie at the smallest distance from the cover 15) and increases with increasing distance—according to the representation in FIG 6 continuously, alternatively in one or more stages - to a higher value. In particular, the permissible maximum value Umax can be at its lowest value up to a first predetermined positioning p and can reach the possible maximum value U0 at a second predetermined positioning p. In the case of the design according to 5 the control device 9 thus determines the permissible maximum value Umax as a function of the positioning p of the electrodes 6.

Of course, also in the case of the design according to 6 as a result, the permissible maximum value Umax depends on the time t. However, the associated functional relationship is not known in advance. In particular, the situation can arise in which the positioning p does not increase continuously, but also temporarily assumes a smaller value again.

It is also possible that the control device 9 (similar to the procedure in steps S6 and S11) by evaluating the time profile of electrical actual variables of the electrical energy supplied to the electrodes 6 and/or by evaluating acoustic actual variables of the electric arc furnace shows a progress in the melting of the metal 2 determined in the arc furnace. For example, the control device 9 in this way the transition from the drilling phase in the remaining part of the melting phase and the transition from the detect melting phase in the flat bath phase. In this case, the control device 9 can determine the permissible maximum value Umax as a function of the progress determined. For example, the control device 9 can set the permissible maximum value Umax as shown in FIG 7 kept at a relatively low value during the drilling phase, kept at a relatively high value (but still below the possible maximum value U0) during the remaining part of the melting phase and ignored during the shallow bathing phase (or alternatively equal to the possible maximum value U0 or to a value above of the possible maximum value U0).

It is the same as shown in FIG 1 possible that the control device 9 accepts an input value E from the operator 16 . In this case, the control device 9 can determine the permissible maximum value Umax as a function of the input value E. The input value E can determine the allowable maximum value Umax alone or in addition to one of the methods of FIG 5 to 7 are taken into account.

The present invention has many advantages. In particular, flashovers of the arcs 13 onto the cover 16 of the furnace vessel 1 and the disadvantages associated therewith can be reliably avoided.

Although the invention has been illustrated and described in detail by the preferred embodiment, the invention is not limited by the disclosed examples and other variants can be derived therefrom by a person skilled in the art without departing from the protective scope of the invention.

Reference List

1

furnace vessel

2

metal

3

power supply device

4

supply network

5

furnace transformer

6

electrodes

7

positioning device

8th

double arrow

9

control device

10

control program

11

machine code

12

molten metal

13

electric arc

14

slag layer

15

operator

16

Lid

A1, A2

control values

E

input value

f0

base frequency

I

electrode currents

p

positioning

p1, p2

predetermined positioning

S1 to S12

steps

t

Time

t1, t2

times

u

electrode voltages

U0

possible maximum value

max

allowed maximum value

X*

target sizes

X

actual values

Claims (8)

Operating method for an electric arc furnace, wherein metal (2) located in a furnace vessel (1) of the electric arc furnace is melted during a melting phase, wherein a control device (9) of the electric arc furnace - Based on electrical setpoint values (X*) of the electrodes (6) to be supplied with electrical energy, provisional voltage setpoints (U1*) are determined, so that when voltages (U) corresponding to the provisional voltage setpoints (U1*) are applied to the electrodes (6), first electrical actual variables (X) of the electrical energy supplied by the electrodes (6) are approximated as closely as possible to the electrical setpoint variables (X*), and - controls an energy supply device (3) of the arc furnace based on final desired voltage values (U2*), so that voltages (U) corresponding to the final desired voltage values (U2*) are applied to the electrodes (6), so that the energy supply device (3) generates electrical obtains energy from a supply network (4) and feeds it to the electrodes (6) via a furnace transformer (5), characterized,
that the control device (9) determines the final desired voltage values (U2*) at least during an initial phase of the melting phase by limiting the provisional desired voltage values (U1*) to a permissible maximum value (Umax), with the permissible maximum value (Umax) being below a possible maximum value (U0 ) which can be applied to the electrodes (6) by the energy supply device (3). Operating method according to claim 1,
characterized,
that the control device (9) receives an input value (E) from an operator (15) and that the control device (9) determines the permissible maximum value (Umax) as a function of the input value (E). Operating method according to claim 1 or 2,
characterized,
that the control device (9) determines the permissible maximum value (Umax) as a function of a period of time that has elapsed since the start of the melting phase. Operating method according to claim 1, 2 or 3,
characterized,
that a positioning (p) of the electrodes (6) varies over time, that the positioning (p) of the electrodes (6) is known to the control device (9) and that the control device (9) determines the permissible maximum value (Umax) as a function of the positioning (p) of the electrodes (6) determined. Operating method according to one of the above claims,
characterized,
that the control device (9) determines the progress of the melting of the metal (2) in the arc furnace by evaluating the time profile of two actual electrical variables (U, I) of the electrical energy supplied to the electrodes (6) and/or by evaluating actual acoustic variables of the arc furnace and that the control device (9) determines the permissible maximum value (Umax) as a function of the determined progress. Control program for a control device (9) of an arc furnace, the control program comprising machine code (11) which can be processed by the control device (9), the processing of the machine code (11) by the control device (9) causing the control device (9 ) operates the arc furnace according to an operating method according to any one of the above claims. Control device of an arc furnace, wherein the control device is programmed with a control program (10) according to claim 6, so that the control device operates the arc furnace according to an operating method according to one of claims 1 to 5. arc furnace, - wherein the arc furnace has a furnace vessel (1) to which metal (2) can be fed, - wherein the arc furnace has an energy supply device (3) and electrodes (6) and a furnace transformer (5), - the energy supply device (3) being connected to a supply network (4) on the input side and to the electrodes (6) via the furnace transformer (5) on the output side, - wherein the arc furnace has a control device (9) by which the energy supply device (3) can be controlled, - wherein the control device (9) is designed according to claim 7.

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