Method and equipment for changing the transformer ratio, impedance or voltage used to excite

Abstract

A method for changing a transformation ratio, an impedance or a voltage used to excite an electric machine 14, the electric machine 14 comprising at least one control winding 3 with winding taps n, n+1 and at least one partial winding 4, 5, and an on-load tap changer 6 for changing the transformation ratio, the impedance or the voltage used to excite the electric machine 14. The on-load tap changer 6 comprises a first module 7 for connecting the winding taps n, n+1 of the control winding 3 and a second module 8 with semiconductor switching elements for coupling, isolating or bypassing the at least one partial winding 4, 5. The method comprises the following steps: receiving a request to change the transformation ratio, the impedance or the voltage used to excite the electric machine 14, checking at least one relevant characteristic value, and changing the transformation ratio, the impedance or the voltage used to excite the electric machine 14 by the first module 7 or the second module 8 depending on the checking of the at least one relevant characteristic value.

Description

[Technical field]

[0001] The present invention relates to a method for varying the transformation ratio, the impedance or the voltage used to excite an electric machine and to an arrangement for varying the transformation ratio, the impedance or the voltage used to excite an electric machine. [Background technology]

[0002] When controlling an energy grid (power grid), a distinction is made between two different time domains. In the so-called steady-state domain, a static operating point is set in the energy grid by suitable electrical equipment, which allows a reliable operation of the energy grid during small load and power fluctuations. In this case, the control is carried out at minute intervals. In the dynamic domain, suitable electrical equipment responds to dynamic fluctuations in the energy grid, which may be caused, for example, by faults or by fast and sometimes exclusively temporary changes in the power and load situation. In this case, very fast control in the millisecond range is required to keep the energy grid stable.

[0003] Since the amount of reactive power varies depending on the respective power and load conditions, reactive power control is an important element of a reliable, efficient and loss-minimizing management of an energy grid.

[0004] Electrical devices suitable for both the control of energy grids in the steady-state region and for dynamic voltage control are already known from the prior art: for example, controllable transformers, phase shifters or controllable shunt reactors are used to control the static operation of energy grids, and for example, static synchronous compensators (STATCOMs) or static var compensators (SVCs) are used to control the dynamic behavior of energy grids.

[0005] Due to power conversion and the integration of distributed power generation facilities into the energy grid system, electrical equipment for control in dynamic areas in particular will continue to become more important in the near future for the management of the energy grid to ensure the supply of electricity, since the supply of electricity from renewable energies is difficult to predict.

[0006] Besides the control of the energy supply network, the different time domains also play an important role in the energy supply (power supply) of an arc furnace. Generally, an electric furnace transformer suitable for supplying an arc contains an on-load tap changer, which allows power control of the electric furnace transformer within a range of a few seconds to a few minutes. However, due to fast changing operating conditions in an arc furnace, such as extinction of the arc used for melting, undesirable effects occur in the arc furnace, such as flicker, which has a time constant in the millisecond range. To suppress the effects of the energy supply network, generally complex and costly compensation devices (SVC) are used.

[0007] An electrical device which allows a combination of control in the steady-state range or in the seconds to minutes range and control in the dynamic range or in the milliseconds range is not yet known from the prior art. Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, the object of the present invention is to provide an improved concept for controlling an energy supply network or an energy supply installation, which provides a combined and flexible control means for operating in both time domains and which is also cost-effective, space-saving and low-loss in operation and manufacture. [Means for solving the problem]

[0009] This problem is solved by a method and an apparatus as set forth in the independent claims. Further embodiments are set forth in the dependent claims.

[0010] The improved concept is based on the idea of ​​combining a typical on-load tap changer, well known from the prior art, with a power electronic on-load tap changer in series with it. The power electronic on-load tap changer changes its switching position fast, i.e. within milliseconds, and thus assumes any position in each case, thus allowing the voltage to be quickly adapted to the fast-changing load behavior. The steady-state region is controlled by the typical on-load tap changer. In this case, the largest possible control range is covered. Energy grids and installations or processes can thus be managed very flexibly.

[0011] According to a first aspect of the improved idea, there is provided a method for varying a transformation ratio, an impedance or a voltage used to excite an electric machine, the electric machine comprising at least one main winding, a control winding having winding taps and at least one partial winding, the electric machine further comprising an on-load tap changer for varying the transformation ratio, the impedance or the voltage used to excite the electric machine.

[0012] The electrical appliance can be configured as a controllable transformer, in particular as a phase-shifting transformer, as a controllable reactor or as a controllable transformer with a capacitor.

[0013] The on-load tap changer comprises a first module for connecting a winding tap of a control winding and a second module having semiconductor switching elements for fast coupling, isolating or bypassing at least one partial winding.

[0014] At least one partial winding preferably has a predetermined number of turns that is greater than the existing maximum number of turns between two adjacent winding taps of the control winding. If the electrical device has multiple partial windings, the numbers of turns of the multiple partial windings may be integer multiples of each other.

[0015] According to one embodiment, the first module is configured as an on-load tap changer for switching on-load between different winding taps of a control winding of an electric machine, and comprises a selector for preselecting in a no-current state the winding tap of the electric machine which has to be changed, and a changeover switch for actually switching on-load the already connected winding tap to the preselected new winding tap. For preselecting the winding tap in a no-current state, the selector typically has two movable selector contacts which connect to the winding taps. For the actual switching, the changeover switch typically has changeover contacts and resistors. The changeover contacts are configured as vacuum valves. The resistors are used for short-term limiting of the circulating current flowing through the changeover switch during the switching process, and are also called current-limiting resistors.

[0016] According to one embodiment, if the electric device has several partial windings, the second module preferably comprises several sub-modules with semiconductor switching elements, at least one partial winding being associated with each sub-module, each sub-module being configured for fast connection, disconnection or bypass of the associated partial winding.

[0017] According to another embodiment, each of the plurality of semiconductor switching elements includes an anti-parallel connected thyristor pair or an IGBT pair.

[0018] A method for changing the transformation ratio, impedance or voltage used to excite an electrical machine, comprising the steps of: a) receiving a request to change the transformation ratio, the impedance or the voltage used to excite the electrical device; b) examining at least one relevant parameter; c) modifying, by the first module or the second module, the transformation ratio, the impedance or the voltage used to excite the electrical device depending on the inspection of the at least one relevant parameter; Includes.

[0019] According to one embodiment, the relevant parameter includes an absolute value of a deviation between an actual voltage of the electrical equipment, for example a voltage on the primary or secondary side of a transformer, and a preset target voltage, and when the absolute value of the deviation from the target voltage is greater than a tap voltage generated between two adjacent winding taps of the control winding, the transformation ratio is changed.

[0020] According to this embodiment, the electrical appliance is configured as a controllable transformer, in other words when the absolute value of the voltage to be controlled or the desired voltage change is large enough that the transformation ratio of the transformer cannot be changed by the operation of the first module, and said change, i.e. the adaptation to a desired target voltage on the primary or secondary side of the transformer, is carried out by the second module.

[0021] According to another embodiment, the relevant parameters include an absolute value of a deviation between the impedance of the electrical device and a preset target impedance, the impedance being modified by the second module when the absolute value of the deviation from the target impedance is greater than an impedance acting between two adjacent winding taps of the control winding.

[0022] According to this embodiment, the electric device is configured as a controllable reactor, in other words, when the impedance to be controlled or the desired impedance change is large enough that the impedance of the reactor cannot be changed by the operation of the first module, said change, i.e. the adaptation to the desired target voltage, is carried out by the second module.

[0023] According to another embodiment, the relevant parameter comprises an absolute value of a deviation between an actual voltage at the first electromagnetic induction device and a preset target voltage for exciting the second electromagnetic induction device, the actual voltage being measured, for example, at the primary side of the first electromagnetic induction device or at the secondary side of the second electromagnetic induction device, such that the voltage used for exciting the second electromagnetic induction device is set by the second module when the absolute value of the deviation from the target voltage is greater than a tap voltage occurring between two adjacent winding taps of the control winding.

[0024] According to this embodiment, the electric device includes a first electromagnetic induction device and a second electromagnetic induction device, and the actual voltage at the first electromagnetic induction device excites the second electromagnetic induction device, thereby increasing the power of the first electromagnetic induction device.

[0025] A second induction device, which is a step-up transformer, is added to the first induction device, which is an excitation transformer, which allows flexible setting of the operating parameters of the on-load tap changer, current and voltage, especially in the case of devices with high power.

[0026] In other words, again, the voltage used to excite the step-up transformer is set by the second module when the absolute value of the voltage desired to excite the step-up transformer is so large that a change cannot be achieved by operation of the first module.

[0027] According to the configuration of this embodiment, the electric device can be configured as a phase shifter, the first electromagnetic induction device can be configured as an excitation transformer, and the second electromagnetic induction device can be configured as a step-up transformer. Therefore, the method can be used to operate a transformer that is a phase shifter as well.

[0028] According to another embodiment, the relevant parameters include a slope of a requested voltage change, the transformation ratio being altered by the second module when the slope of the requested voltage change is greater than a defined limit value.

[0029] According to this embodiment, the electric appliance is configured as a controllable transformer. In other words, the change of the transformer ratio, i.e. the adaptation to the desired target voltage on the primary or secondary side of the transformer, is carried out by the second module when the gradient of the required voltage change is so large that the transformation ratio cannot be changed fast enough by the first module, for example when the required change speed of the voltage is in the range of milliseconds. Accordingly, the defined limit value is, for example, about 1 second.

[0030] According to another embodiment, the relevant parameters include a slope of a requested impedance change, the impedance being altered by the second module when the slope of the requested impedance change is greater than a defined limit value.

[0031] According to this embodiment, the electric device is configured as a controllable reactor, in other words, the change of the impedance of the reactor, i.e. the adaptation to the target impedance, is carried out by the second module when the gradient of the required impedance change is so large that the impedance cannot be changed fast enough by the first module, for example when the required change speed of the impedance is in the range of milliseconds. Accordingly, the defined limit value is, for example, about 1 second.

[0032] According to another embodiment, the relevant parameter comprises a fundamental plus harmonic content of the voltage generated by the electrical appliance, the transformation ratio being modified by the second module when the harmonic content is greater than a defined limit value.

[0033] According to this embodiment, the electrical equipment is configured as a controllable transformer. In other words, when harmonic components are superimposed on the fundamental oscillation of the voltage applied to the transformer to such an extent that the harmonics can no longer be controlled by the first module, a change in the transformation ratio of the transformer, i.e. an adaptation to a desired target voltage on the primary or secondary side of the transformer, is carried out by the second module. The definition of the limit values ​​depends on the respective configuration of the installation and the connection conditions of the energy supply network.

[0034] According to another embodiment, a Fourier analysis is carried out in order to determine the harmonic components superimposed on the fundamental oscillation of the voltage generated by the electrical equipment, preferably the voltage applied to the connection side of the electrical function to the energy supply network.

[0035] According to another embodiment, after changing the transformation ratio, the impedance or the voltage used for magnetizing by the second module, the first and second modules are operated such that the second module assumes a neutral position in which the at least one partial winding is bypassed, i.e. bypassed means that it is energized but not energized, in other words, the semiconductor switching elements of the second module are connected to each other such that at least one partial winding is bypassed.

[0036] According to one embodiment, the first and second modules are operated alternately.

[0037] According to another embodiment, the first and second modules are operated alternately until the first module reaches a position which represents a new static operating point of the energy supply network and the second module is located in a neutral position.

[0038] In other words, the turns ratio is set by switching between the winding taps of the control winding by means of the first module, during which at least one partial winding is newly isolated by stepwise operating the semiconductor switching elements of the second module, so that the first module follows stepwise after switching of the second module. Finally, the on-load tap changer is in a position in which the first module newly assumes a new static operating point and the second module is in a neutral position.

[0039] Advantageously, in this embodiment, the on-load tap changer is now at the starting point where at least one partial winding is no longer energized, and the entire control range is provided to the bidirectional second module starting from the neutral position.

[0040] According to another embodiment, after changing the transformation ratio, the impedance or the voltage used for magnetization by the second module, the first module and the second module are operated to assume this first end position in which the entire dynamic control range of the second module is applicable from the first end position to the second end position.

[0041] For example, in a first end position of the second module, at least one partial winding is connected to the control winding, i.e. a winding of the partial winding is added to the control winding, and in a second end position, the partial winding is separated from the control winding, i.e. a winding of the partial winding is removed from the control winding.

[0042] Advantageously, in this embodiment the full control range of the second module is provided for a given demand on the energy grid which requires a fast response in one direction.

[0043] According to another embodiment, a number of relevant parameters are examined, the relevance of the number of relevant parameters is weighted, and the transformation ratio, the impedance or the voltage used for excitation is modified by the first module or the second module depending on the examination and the weighting of the number of relevant parameters.

[0044] According to one embodiment, the first module and the second module are not operated simultaneously.

[0045] According to a second aspect of the improved idea, there is provided an arrangement for varying the transformation ratio, the impedance or the voltage used to excite an electric machine, preferably arranged to carry out the method according to the first aspect of the invention.

[0046] With regard to the device, reference is made to the above contents, preferred features, effects and / or advantages already explained for the method, therefore the corresponding repetition will be omitted.

[0047] The electrical machine has at least one main winding, one control winding with winding taps, at least one partial winding and one on-load tap changer for changing the transformation ratio, the impedance or the voltage used to excite the electrical machine.

[0048] The installation comprises at least one sensor 10 for measuring the voltage occurring at a suitable measuring point and / or at least one sensor 10 for measuring the current flowing at a suitable measuring point.

[0049] Furthermore, the installation comprises an evaluation device configured to carry out the method according to the first aspect of the improved idea.

[0050] According to one embodiment, the on-load tap changer comprises a first module for connecting the winding tap of the control winding and a second module having semiconductor switching elements for coupling, isolating or bypassing the at least one partial winding, the first module comprises a first control device and the second module comprises a second control device, the evaluation device is configured to operate the first control device and the second control device.

[0051] According to one embodiment, the first module is configured as an on-load tap changer for switching on-load between different winding taps of a control winding of an electric machine and comprises a selector for preselecting in the no-current state the winding tap of the electric machine which has to be changed and a changeover switch for actually switching on-load an already connected winding tap to a preselected new winding tap. For preselecting the winding tap in the no-current state, the selector typically has two movable selector contacts which are connected to the winding taps. For the actual switching, the changeover switch typically has mechanical changeover contacts, e.g. a vacuum valve.

[0052] According to another embodiment, the first control device is configured as a motor drive which operates the contacts of the selector and the changeover contacts of the on-load tap changer.

[0053] According to one embodiment, in case the electric device has several partial windings, the second module comprises at least one, preferably several sub-modules with semiconductor switching elements, at least one partial winding being associated with each sub-module, each sub-module being configured for fast connection, disconnection or bypass of the associated partial winding.

[0054] According to another embodiment, the second control device is configured to appropriately operate at least one or more sub-modules or semiconductor switching elements associated with said sub-modules such that at least one partial winding or multiple partial windings are quickly connected to the control winding or quickly disconnected from the control winding or quickly bypassed.

[0055] The second control device is configured, for example, as a microcontroller.

[0056] The present invention will be described in detail below with reference to the figures based on the illustrated embodiments. Components that are identical or functionally identical or have the same effect are indicated by the same reference numerals. In some cases, the same components or components with the same function are only described for the figure in which they first appear. The description is not necessarily repeated in the subsequent figures. [Brief description of the drawings]

[0057] [Figure 1] 1 shows a schematic diagram of a first embodiment of an installation according to an improved concept. [Diagram 2] 2 shows a schematic representation of a second embodiment of the installation; [Diagram 3] 3 shows diagrammatically a third embodiment of the installation; [Figure 4] 4 shows a schematic representation of a fourth embodiment of the installation. [Diagram 5] 5 shows a schematic representation of a fifth embodiment of the installation. [Figure 6] 6 shows a schematic representation of a sixth embodiment of the installation. [Figure 7] A preferred embodiment of the method according to the improved concept is shown. [Figure 8] 4 shows the control range of an on-load tap changer in a plant according to an embodiment of the method of the improved idea. [Figure 9] 4 shows another control range of an on-load tap changer in a plant according to another embodiment of the method according to the improved idea; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0058] In FIG. 1 a preferred embodiment of an installation 1 according to the improved concept is shown diagrammatically.

[0059] The installation 1 is used to change the transformation ratio of an electrical machine 14, which is configured here as a controllable single-phase transformer. The controllable transformer 14 has on the primary or secondary side a main winding 2, one control winding 3 with n winding taps and two partial windings 4 and 5.

[0060] The partial winding 5 has a larger number of turns, for example three times larger, than the partial winding 4. Furthermore, the number of turns of the partial winding 4 and the number of turns of the partial winding 5 are larger than the existing maximum number of turns between two adjacent winding taps of the control winding 3, for example between n and n+1.

[0061] The number of these partial windings is not limited to two. In principle, more partial windings may be provided. The number of turns of these partial windings may each be an integer multiple of the number of turns of the partial winding 4.

[0062] Furthermore, the transformer 14 comprises an on-load tap changer 6 for varying the transformation ratio of the transformer 14. The on-load tap changer 6 comprises a first module 7 for connecting the winding taps n, n+1 of the control winding 3 and a second module 8 connected in series with the first module 7 for coupling, isolating or bypassing the partial windings 4, 5. The first module 7 is provided for control in the steady-state domain and the second module 8 is provided for control in the dynamic time domain.

[0063] Preferably, the first module 7 is configured as an on-load tap changer, which consists of a selector for preselecting the winding taps n, n+1 in the no-current state and a changeover switch for switching the already connected winding tap n to the preselected new winding tap n+1 on-load. Furthermore, the on-load tap changer may have a preselector (Vorwaehler), which may be configured as a sparse tap selector (Grobstufe) or a changeover selector (Wender). However, in FIG. 1, for the sake of better clarity, the first module 7 is shown very simply.

[0064] Preferably, the second module 8 comprises two submodules with semiconductor switching elements, for example anti-parallel connected thyristor pairs or IGBT pairs. A respective partial winding 4 or 5 is associated with each submodule, which is configured to couple or disconnect the respective partial winding 4 or 5 to the control winding 3 or to bypass the respective partial winding 4 or 5 by means of said semiconductor switching elements quickly, i.e. within 10 to 1000 milliseconds, so that the partial windings 4, 5 have a predetermined potential but are not energized. For the sake of clarity, the second module 8 is also shown in a highly simplified manner in FIG. 1.

[0065] Furthermore, the installation 1 comprises a voltage sensor 9 and a current sensor 10. Here, the voltage sensor 9 is arranged, for example, at a high voltage terminal of the main winding 2 and is configured to measure the voltage of the electrical appliance or the actual voltage. The current sensor 10 is arranged between the second module 8 and the load earth conductor 15 and is configured to measure the current flowing between the second module 8 and the load earth conductor 15.

[0066] The first module 7 comprises a first control device 11, preferably configured as a motor drive, which operates the selector and the diverter switch mechanically, for example by means of a drive system having a gear mechanism.

[0067] The second module 8 is controlled by a second control device 12. The second control device 12 is configured to appropriately operate the two submodules or the semiconductor switching elements associated with these submodules, such that the two partial windings 4 or 5 are quickly coupled to or quickly decoupled from the control winding 3 or the two partial windings 4 and 5 are quickly bypassed. The second control device 12 is configured, for example, as a microcontroller or as an IGBT driver.

[0068] The first control device 11 and the second control device 12 are operated by an evaluation device 13 in a mutually dependent manner.

[0069] A second embodiment of the inventive installation 1 is shown diagrammatically in figure 2. The installation 1 according to figure 2 is similar to the installation according to figure 1 described above, and in the following only the differences with respect to the installation according to figure 1 will be explained.

[0070] FIG. 2 shows an arrangement 1 for varying the impedance of an electric machine 14, here configured as a controllable inductance. Such an arrangement is used in an energy supply network to control reactive power. In addition to the main winding 2, the control winding 3 with n winding taps and the two partial windings 4 and 5, the controllable inductance 14 further comprises a sparse tap winding 16 and a sparse tap control 17. The sparse tap control 17 takes a first position in which the sparse tap control 17 contacts a first end A of the sparse tap winding 16 and a second position in which the sparse tap control 17 contacts a second end B of the sparse tap winding 16. When the sparse tap control 17 is in the first position, the sparse tap winding 16 is not energized. On the other hand, when the sparse tap control 17 is in the second position, a current is energized in the sparse tap winding 16 and is thus added to the main winding 2 and to the control winding 3. In this way, the control range of the inductance 14 is increased. The consumption of reactive power from the energy grid is controlled by the installation 1 according to this embodiment.

[0071] A third embodiment of the inventive installation 3 is shown diagrammatically in figure 3. The installation 1 according to figure 3 is similar to the installation according to figures 1 and 2 above, and in the following only the differences will be explained.

[0072] 3 shows an installation 1 for changing the transformation ratio of an electrical machine 14, here configured as a controllable transformer 14 with a connected capacitor 18. The supply of capacitive reactive power to the energy supply grid is controlled by the installation 1 according to this embodiment. The controllable transformer 14 comprises, for example, a main winding 2 with a series winding 19, a control winding 3 and a load earth wire 15. The capacitor 18 is arranged between the first module 7 and the second module 8 of the on-load tap changer.

[0073] In figure 4 a fourth embodiment of the inventive arrangement 1 is shown diagrammatically, which shows an arrangement 1 for changing the transformation ratio of an electric machine 14 configured as a controllable transformer 14 with a connected capacitor 18 in a similar manner to figure 3. The arrangement 1 according to figure 4 is therefore also similar to the arrangements according to figures 1, 2 and 3 described above, and in the following only the differences will be described.

[0074] In this embodiment, the controllable transformer 14 comprises a main winding 2, a control winding 3 with n winding taps, two partial windings 4 and 5 and an additional sparse tap winding 16 with a sparse tap control 17. A capacitor 18 for supplying capacitive reactive power to the energy supply grid is arranged in a line 20 branching between the main winding 2 and the sparse tap winding 16 and terminating in the load earth line 15.

[0075] A fifth embodiment of the installation 1 according to the invention is shown diagrammatically in figure 5. The installation 1 according to figure 5 is similar to the installations according to figures 1, 2, 3 and 4 above, and in the following only the differences will be explained.

[0076] FIG. 5 shows an installation 1 for changing the voltage used to excite an electric machine 14, for example for use in an arc furnace. Here, the electric machine 14 is composed of a first electromagnetic induction device 22 configured as an excitation transformer and a second electromagnetic induction device 23 configured as a step-up transformer. The excitation transformer 22 comprises a main winding 2, a control winding 3 with n winding taps and two partial windings 4 and 5. The step-up transformer 23 has a primary winding 24 and a secondary winding 25, with the arc furnace 21 arranged on the secondary side. The control winding 3 of the excitation transformer 22 is conductively connected to the primary winding 24 of the step-up transformer 23. In this embodiment, the voltage of the excitation transformer 22 used to excite the step-up transformer 23 is controlled by an on-load tap changer 6. Depending on whether the control is to be performed in the steady-state region or in the dynamic region, a first module 7 or a second module 8 is used.

[0077] A sixth embodiment of the installation 1 according to the invention is shown diagrammatically in figure 6. The installation 1 according to figure 6 is similar to the installations according to figures 1, 2, 3, 4 and 5 above, and in the following only the differences will be explained.

[0078] Another installation 1 for changing the voltage used to excite an electric machine 14, for example as used in an arc furnace, is shown. Here again the electric machine 14 is composed of a first electromagnetic induction device 22 configured as an excitation transformer and a second electromagnetic induction device 23 configured as a step-up transformer. In this embodiment, the excitation transformer 22 has a primary winding 24 and a secondary winding 27, and the step-up transformer 23 has a control winding 24 on the primary side. The secondary winding 27 of the excitation transformer 22 is conductively connected to the control winding 24 or the primary side of the step-up transformer 23. In the control winding 24 of the step-up transformer 23, the voltage excited in the step-up transformer 23 by the excitation transformer 22 is controlled by an on-load tap changer 6.

[0079] FIG. 7 shows a preferred embodiment of the method according to the improved idea. The method is executed by an installation as already described according to one of the embodiments according to FIGS. 1 to 6. In step a, a request to change the transformation ratio, the impedance or the voltage used to excite the electrical equipment 14 is received. This request can be sent from a higher-level system, for example from a central control room of the energy grid operator, or from a local control device, for example a voltage controller. Then, in step b, at least one relevant parameter is checked, and in step c, the transformation ratio, the impedance or the voltage used to excite the electrical equipment 14 is changed by the first module 7 or the second module 8 of the on-load tap changer 6 depending on the checking of the at least one relevant parameter.

[0080] Steps b and c are carried out by an evaluation device 13 which controls the first control device 11 or the second control device 12 depending on the check carried out in step b.

[0081] In step b, various relevant parameters can be checked. For example, the relevant parameter can be the absolute value of the deviation between the actual voltage of the electrical appliance 14 and a preset target voltage. For this, the actual voltage or the voltage of the electrical appliance is measured by the voltage sensor 9 and the measured value is compared with the preset target voltage by the evaluation device 13. In this case, the transformation ratio is changed when the absolute value of the deviation from the target voltage is greater than the tap voltage occurring between two adjacent winding taps of the control winding 3, for example between n and n+1. Another example for a relevant parameter that can be checked is the absolute value of the deviation between the impedance of the electrical appliance 14 and a preset target impedance. For this, the impedance of the electrical appliance 14 is calculated based on the current values ​​measured by the current sensor 10 and the calculated value is compared with the preset target impedance by the evaluation device 13. The impedance is then changed by the second module 8 when the absolute value of the deviation from the target impedance is greater than the impedance acting between two adjacent winding taps n, n+1 of the control winding 3. Further examples for the relevant parameters are the gradient of the required voltage change, the gradient of the required impedance change or the absolute value of the deviation between the actual voltage at the first electromagnetic induction device 22 and a preset target voltage for exciting the second electromagnetic induction device 23.

[0082] Once the transformation ratio, the impedance or the voltage used for excitation has been changed by the second module 8, the first module 7 and the second module 8 are subsequently operated alternately, according to a preferred implementation of the method, until the first module 7 reaches a position which represents a new static operating point of the energy supply network or process operating system and the second module 8 is in a neutral position (at which potential the partial windings 4 and 5 are bypassed, i.e. are supplied with potential but are not energized).

[0083] In other words, after the switching of the second module 8, the first module 7 is "followed" step by step. For example, if the second module 8 is switched from the neutral position (0) to two steps up (+2), then in the next step the first module 7 is switched one step up (+1) and the second module is switched anew one step down (-1). In the next step the first module 7 is again switched one step up (+1) and the second module 8 is again switched one step down (-1). Finally, the first module 7 is two steps higher than the beginning and the second module 8 is again back to its neutral position. This "following" of the first module 7 sets the first module 7 to a new static operating point. The entire control range starting from the neutral position and going up or down is provided to the second module 8.

[0084] The above explanation regarding the varying impedance is illustrated in FIG. 8. Here, the control range of the on-load tap changer 6, more specifically the control range of the reactive power, is illustrated. On the y-axis, the reactive power of the induction device 14 is expressed as a percentage. On the x-axis, the position of the first module 7 of the on-load tap changer 6, i.e. which winding tap n of the control winding 3 is contacted by the first module 7 of the on-load tap changer 6, can be read. In this case, the point 28 indicates the possible positions that the first module 7 can take. In this case, the control is performed within the steady-state range, i.e. at minute intervals. The point 30 indicates the static operating point set by the first module 7 according to this embodiment. The range delimited by the line 29, which starts from the point 28 or 30 and runs vertically up or down, is the control range covered by the second module 8. Within this range, limited by the line 29, the control is performed fast, i.e. in the millisecond range, bidirectionally, by the second module 8, so as to be able to respond flexibly and quickly to dynamic fluctuations in the energy supply network or installation. Thus, fast but expensive semiconductor switching elements do not need to be applied to the entire control range of the on-load tap changer 6, but only to the range that must be controlled quickly.

[0085] FIG. 9 illustrates another control range of the on-load tap changer 6, more specifically the control range of the reactive power according to another embodiment of the method. According to this embodiment, the first module 7 and the second module 8 are operated such that the second module 8 assumes a first end position in which both windings of the partial windings 4 and 5 are added to or subtracted from the control winding 3, after changing the transformation ratio, the impedance or the voltage used for magnetization by the second module 8. In the case of this embodiment, the respective end position represents an operating point 30. Depending on which situation applies, the entire dynamic control range of the second module 8 is applicable in one direction starting from the operating point 30, i.e. from the first end position to the second end position or from the second end position to the first end position. This configuration is beneficial for certain energy supply network conditions that require a fast response of the on-load tap changer 6 in one direction.

[0086] Combining a conventional on-load tap changer of a first module with a power electronic on-load tap changer (second module) makes it highly possible to realize a wide control range while simultaneously ensuring a low-cost and space-saving arrangement. That is to say, the second module for faster control within the dynamic control range, which is more expensive than the first module, can be optimally designed for the respective application. As a result, the second module can be appropriately designed only for the part of the control where the power electronics-based second module takes advantage due to its switching speed. Furthermore, the combined solution is significantly more space-saving than a purely power electronics-based solution. In conclusion, with the inventive solution, network management and operation of the furnace can be achieved very flexibly with a relatively small space requirement. [Explanation of symbols]

[0087] 1 equipment 2 Main Winding 3 Control Winding 4 First partial winding 5 Second partial winding 6 On-load tap changer 7 6 1st module 8 6 2nd module 9 Voltage Sensor 10 Current Sensor 11 First control device 12 Second control device 13 Evaluation equipment 14 Electrical Equipment 15 Load earth wire 16 Sparse tap winding (transposition tap winding) 17 Sparse tap control section (transposition tap control section) 18 Capacitor 19 Series Winding 20 Electric wire 21 Electric Arc Furnace 22 1st electromagnetic induction device 23 Second electromagnetic induction device 24 Primary winding of 23 or control winding of 23 25 23 secondary winding 26 22 Primary Winding 27 22 secondary winding 28 points 29 lines A 16 first end B 16 2nd end n-1,n,…n+4 Winding taps

Claims

1. 1. A method for changing the transformation ratio, impedance or voltage used to excite an electric machine (14), said electric machine (14) comprising: at least one control winding (3) and at least one partial winding (4, 5) with winding taps (n, n+1), - on-load tap changers (6) for changing the transformation ratio, the impedance or the voltage used to excite the electrical machines (14), the on-load tap changer (6) comprises a first module (7) for connecting the winding taps (n, n+1) of the control winding (3) and a second module (8) with semiconductor switching elements for coupling, isolating or bypassing the at least one partial winding (4, 5), The method comprises the steps of: - receiving a request to change the transformation ratio, the impedance or the voltage used to excite the electrical machine (14); - examining at least one relevant characteristic value; - modifying the transformation ratio, the impedance or the voltage used to excite the electrical machine (14) by the first module (7) or the second module (8) depending on the inspection of the at least one relevant characteristic value; The method includes:

2. the relevant characteristic value comprises the absolute value of the deviation between the actual voltage of the electrical appliance (14) and a preset target voltage; 2. The method of claim 1, wherein the transformation ratio is changed by the second module (8) when the absolute value of the deviation from the target voltage is greater than the tap voltage occurring between two adjacent winding taps (n, n+1) of the control winding (3).

3. the relevant characteristic value comprises the absolute value of the deviation between the impedance of the electrical device (14) and a preset target impedance; 3. A method according to claim 1 or 2, characterized in that the impedance is modified by the second module (8) when the absolute value of the deviation from the target impedance is greater than the impedance acting between two adjacent winding taps (n, n+1) of the control winding (3).

4. the relevant characteristic value comprises the absolute value of the deviation between the actual voltage of the first electromagnetic induction device (22) for exciting the second electromagnetic induction device (23) and a preset target voltage; 3. The method according to claim 1 or 2, wherein the voltage used to excite the second electromagnetic induction device (23) is set by the second module (8) when the absolute value of the deviation from the target voltage is greater than the tap voltage occurring between two adjacent winding taps (n, n+1) of the control winding (24).

5. - the relevant characteristic value comprises the slope of the required voltage change; A method according to claim 1 or 2, characterized in that the transformation ratio is changed by the second module (8) when the gradient of the requested voltage change is greater than a defined limit value.

6. - the relevant characteristic value comprises the gradient of the required impedance change; A method according to claim 1 or 2, wherein the impedance is modified by the second module (8) when the gradient of the requested impedance change is greater than a defined limit value.

7. - the relevant characteristic value comprises the fundamental plus harmonic components of the voltage generated by the electrical appliance (14); A method according to claim 1 or 2, characterized in that the transformation ratio is modified by the second module (8) when the harmonic content is greater than a defined limit value.

8. A method according to claim 7, in which a Fourier analysis is carried out to determine the harmonic components superimposed on the fundamental vibration of the voltage generated by the electrical machine (14).

9. - after modifying the transformation ratio, the impedance or the voltage used for magnetizing by the second module (8), The method according to claim 1 or 2, wherein the first module (7) and the second module (8) are operated such that the second module (8) assumes a neutral position in which the at least one partial winding (4, 5) is bypassed.

10. - after modifying the transformation ratio, the impedance or the voltage used for magnetizing by the second module (8), The method according to claim 1 or 2, wherein the first module (7) and the second module (8) are operated to assume a first end position in which the entire dynamic control range of the second module (8) is applicable from the first end position to the second end position.

11. - multiple relevant property values ​​are examined; - the relevance of said plurality of relevant characteristic values ​​is weighted; 3. A method according to claim 1 or 2, wherein the transformation ratio, the impedance or the voltage used for magnetizing is modified by the first module (7) or the second module (8) depending on said examination and said weighting of said plurality of relevant characteristic values.

12. The method according to claim 1 or 2, wherein the first module (7) and the second module (8) are not operated simultaneously.

13. An arrangement (1) for changing the transformation ratio, the impedance or the voltage used to excite an electric machine (14), the electric machine (14) comprising at least one control winding (3) with winding taps (n, n+1), at least one partial winding (4, 5) and an on-load tap changer (6) for changing the transformation ratio, the impedance or the voltage used to excite the electric machine (14), the arrangement (1) comprising: - at least one sensor (9) for measuring the voltage occurring at a suitable measuring point; - at least one sensor (10) for measuring the current passing through it at a suitable measuring point; an evaluation device (13) configured to carry out the method according to claim 1 or 2; The facility (20) includes at least one of:

14. the on-load tap changer (6) comprises a first module (7) for connecting the winding taps (n, n+1) of the control winding (3) and a second module (8) with semiconductor switching elements for coupling, isolating or bypassing the at least one partial winding (4, 5), - said first module (7) comprises a first control device (11), - said second module (8) comprises a second control device (12), The installation (20) according to claim 13, wherein the evaluation device (13) is adapted to operate the first control device (11) and the second control device (12).

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